United Halogen Bulb is a discount supplier of name brand and quality imported halogen light bulbs, quality halogen bulb sockets, and accessories.Our mission is to supply you, the customer with a quality product at a fair price. Our mission also includes keeping up to date with technological innovations in the lighting industry. As new technology in lighting and LED technology improves you will see those products here.

Halogen Light bulbs are what we do—we stock the hard to find products that you are looking for. We carry the largest line of halogen bulb sockets, transformers, and both low voltage and line voltage halogen bulbs at the best prices available.

We also stock a complete line of lamp sockets for halogen light bulbs. If you build your own halogen lamps or you just want to repair a halogen lamp, we have the parts for you. We stock transformers, dimmers and light bulb sockets for all types of halogen light bulbs.

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The Great Internet Light Bulb Book, Part IIncandescent including halogen light bulbs Copyright (C) 1996, 2000, 2005, 2006 Donald L. Klipstein (Jr) (don@donklipstein.com) Freely distributing copies of this entire document or un-HTML-ized text versions thereof is permitted and encouraged. History Basic principles Luminous efficiency Vacuum vs. gas-filled bulbs How bulbs burn out Why bulbs often burn out when you turn them on Why burnout is sometimes so spectacular How bad a current surge bulbs draw when turned on Making bulbs last longer Long-life bulbs Reduced power Soft start devices DC vs. AC operation Why making bulbs last longer often does not pay How to minimize lighting costs Halogen bulbs The halogen cycle Lifetime and efficiency of halogen bulbs Halogen bulb failure modes Use of halogen bulbs with dimmers Ultraviolet from halogen bulbs History of Incandescent Bulbs It is widely regarded that Thomas Alva Edison invented the first reasonably practical incandescent lamp, using a carbon filament in a bulb containing a vacuum. Edison's first successful test occurred in 1879. There were earlier incandescent lamps, such as one by Heinrich Goebel made with a carbon filament in 1854. This incandescent lamp had a carbonized bamboo filament and was mentioned as lasting up to 400 hours. At least some sources regard Goebel as the inventor of the incandescent lamp. Joseph Wilson Swan began trying to make carbon-based incandescent lamps in 1850 and made one in 1860 that was workable except for excessively short life due to poor vacuum. He made more successful inccandescent lamps after better vacuum pumps became available in the mid 1870's. Since that time, the incandescent lamp has been improved by using tantalum and later tungsten filaments, which evaporate more slowly than carbon. Nowadays, incandescent lamps are still made with tungsten filaments. Basic Principles The filament of an incandescent lamp is simply a resistor. If electrical power is applied, it is converted to heat in the filament. The filament's temperature rises until it gets rid of heat at the same rate that heat is being generated in the filament. Ideally, the filament gets rid of heat only by radiating it away, although a small amount of heat energy is also removed from the filament by thermal conduction. The filament's temperature is very high, generally over 2000 degrees Celsius, or generally over 3600 degrees Fahrenheit. In a "standard" 75 or 100 watt 120 volt bulb, the filament temperature is roughly 2550 degrees Celsius, or roughly 4600 degrees Fahrenheit. At high temperatures like this, the thermal radiation from the filament includes a significant amount of visible light. For more info on incandescent lamps, try these pages at Bulbs.com: Incandescent Lamp Workings The incandescent lamp top page at "Lightbulb University" at Bulbs.com. Luminous Efficiency In a 120 volt, 100 watt "standard" bulb with a rated light output of 1750 lumens, the efficiency is 17.5 lumens per watt. This compares poorly to an "ideal" of 242.5 lumens per watt for one idealized type of white light, or 683 lumens per watt ideally for the yellowish-green wavelength of light that the human eye is most sensitive to. Other types of incandescent light bulbs have different efficiencies, but all generally have efficiencies near or below 35 lumens per watt. Most household incandescent bulbs have efficiencies from 8 to 21 lumens per watt. Higher efficiencies near 35 lumens per watt are only achieved with photographic and projection lamps with very high filament temperatures and short lifetimes of a few hours to around 40 hours. The reason for this poor efficiency is the fact that tungsten filaments radiate mostly infrared radiation at any temperature that they can withstand. An ideal thermal radiator produces visible light most efficiently at temperatures around 6300 Celsius (6600 Kelvin or 11,500 degrees Fahrenheit). Even at this high temperature, a lot of the radiation is either infrared or ultraviolet, and the theoretical luminous efficiency is 95 lumens per watt. Of course, nothing known to any humans is solid and usable as a light bulb filament at temperatures anywhere close to this. The surface of the sun is not quite that hot. There are other ways to efficiently radiate thermal radiation using higher temperatures and/or substances that radiate better at visible wavelengths than invisible ones. This is covered by Part II of the Great Internet Light Bulb Book, Discharge Lamps. The efficiency of an incandescent bulb can be increased by increasing the filament temperature, which makes it burn out more quickly. Vacuum vs. gas-filled bulbs At first, incandescent bulbs were made with a vacuum inside them. Air oxidizes the filament at high temperatures. Later, it was discovered that filling the bulb with an inert gas such as argon or an argon-nitrogen mixture slows down evaporation of the filament. Tungsten atoms evaporating from the filament can be bounced back to the filament by gas atoms. The filament can be operated at a higher temperature with a fill gas than with a vacuum. This results in more efficient radiation of visible light. So why are some bulbs still made with a vacuum? The reason is that a fill gas conducts heat away from the filament. This conducted heat is energy that cannot be radiated by the filament and is lost, or wasted. This mechanism reduces the bulb's efficiency of producing radiation. If this is not offset by the advantage of operating the filament at a higher temperature, then the bulb is more efficient with a vacuum. One property of thermal conduction from the filament to the gas is the strange fact that the amount of heat conducted is roughly proportional to the filament's length, but does not vary much with the filament's diameter. The reason this occurs is beyond the scope of this document. However, this means that bulbs with thin filaments and lower currents are more efficient with a vacuum, and higher current bulbs with thicker filaments are more efficient with a fill gas. The break-even point seems to be very roughly around 6-10 watts per centimeter of filament. (This can vary with filament temperature and other factors. The break-even point may be higher in larger bulbs where convection may increase heat removal from the filament by the gas.) Sometimes, premium fill gases such as krypton or xenon are used. These gases have larger atoms that are better at bouncing evaporated tungsten atoms back to the filament. These gases also conduct heat less than argon. Of these two gases, xenon is better, but more expensive. Either of these gases will significantly improve the life of the bulb, or result in some improvement in efficiency, or both. Often, the cost of these gases makes it uneconomical to use them. How light bulbs burn out Due to the high temperature that a tungsten filament is operated at, some of the tungsten evaporates during use. Furthermore, since no light bulb is perfect, the filament does not evaporate evenly. Some spots will suffer greater evaporation and become thinner than the rest of the filament. These thin spots cause problems. Their electrical resistance is greater than that of average parts of the filament. Since the current is equal in all parts of the filament, more heat is generated where the filament is thinner. The thin parts also have less surface area to radiate heat away with. This "double whammy" causes the thin spots to have a higher temperature. Now that the thin spots are hotter, they evaporate more quickly. It becomes apparent that as soon as a part of the filament becomes significantly thinner than the rest of it, this situation compounds itself at increasing speed until a thin part of the filament either melts or becomes weak and breaks. Why bulbs often burn out when you turn them on Many people wonder what goes on when you turn on a light. It is often annoying that a weak, aging light bulb will not burn out until the next time you turn it on. The answer here is with those thin spots in the filament. Since they have less mass than the less-evaporated parts of the filament, they heat up more quickly. Part of the problem is the fact that tungsten, like most metals, has less resistance when it is cool and more resistance when it is hot. This explains the current surge that light bulbs draw when they are first turned on. When the thin spots have reached the temperature that they would be running at, the thicker, heavier parts of the filament have not yet reached their final temperature. This means that the filament's resistance is still a bit low and excessive current is still flowing. This causes the thinner parts of the filament to get even hotter while the rest of the filament is still warming up. This means that the thin spots, which run too hot anyway, get even hotter when the thicker parts of the filament have not yet fully warmed up. This is why weak, aging bulbs can't survive being turned on. Why burnout is sometimes so spectacular When the filament breaks, an arc sometimes forms. Since the current flowing through the arc is also flowing through the filament at this time, there is a voltage gradient across the two pieces of the filament. This voltage gradient often causes this arc to expand until it is across the entire filament. Now, consider a slightly nasty characteristic of most electric arcs. If you increase the current going through an arc, it gets hotter, which makes it more conductive. Obviously, this could make things a bit unstable, since the more conductive arc would draw even more current. The arc easily becomes conductive enough that it draws a few hundred amps of current. At this point, the arc often melts the parts of the filament that the ends of the arc are on, and the arc glows with a very bright light blue flash. Most household light bulbs have a built-in fuse, consisting of a thin region in one of the internal wires. The extreme current drawn by a burnout arc often blows this built-in fuse. If not for this fuse, people would frequently suffer blown fuses or tripped circuit breakers from light bulbs burning out. Although the light bulb's internal fuse will generally protect household fuses and circuit breakers, it may fail to protect the more delicate electronics often found in light dimmers and electronic switching devices from the current surges drawn by "burnout arcs". How bad a current surge bulbs draw when turned on It is fairly well known that a cold light bulb filament has less resistance than a hot one. Therefore, a light bulb draws excessive current until the filament warms up. Since the filament can draw more than ten times as much current as usual when it is cold, some people are concerned about excessive energy consumption from turning on light bulbs. The degree of this phenomenon has become a matter of urban folklore. However, the filament warms up very rapidly. The amount of energy consumed to warm up a cold filament is less than it would consume in one second of normal operation. Making bulbs last longer Long-life bulbs Many light bulbs are made to operate with a slightly lower filament temperature than usual. This makes the bulbs last much longer with a slight reduction of efficiency. Reduced Power Reducing the voltage applied to a light bulb will reduce the filament temperature, resulting in a dramatic increase in life expectancy. One device sold to do this is an ordinary silicon diode built into a cap that is made to stick to the base of a light bulb. A diode lets current through in only one direction, causing the bulb to get power only 50 percent of the time if it is operated on AC. This effectively reduces the applied voltage by about 30 percent. (Reducing the voltage to its original value times the square root of .5 results in the same power consumption as applying full voltage half the time.) The life expectancy is increased very dramatically. However, the power consumption is reduced by about 40 percent (not 50 since the cooler filament has less resistance) and light output is reduced by reduced by about 70 percent (cooler filaments are less efficient at radiating visible light). Soft-start devices Since bulbs usually burn out during the current surge that occurs when they are turned on, one would expect that eliminating the surge would save light bulbs. In fact, such devices are available. Like the diode-based ones, they are available in a form that is built into caps that one could stick onto the tip of the base of a light bulb. These devices are "negative temperature coefficient thermistors", which are resistors having a resistance that decrease when they heat up. When the bulb is first started, the thermistor is cool and has a moderately high resistance that limits current flowing through the bulb. The current flowing through the thermistor's resistance generates heat, and the thermistor's resistance decreases. This allows the current to increase in a fairly gradual manner, and the filament warms up in a uniform manner. However, this extends the life of the bulbs less than one might think. If the filament has thin spots that cannot survive the current surge that occurs when the bulb is turned on, then the filament is already in very bad shape. At this time, the thin spots are significantly hotter than the thicker parts of the filament and are evaporating rather rapidly. As described earlier, this process is accelerating. If the thin spots are protected from surges, the life of the bulb would be extended by only a few percent. Additional life extension occurs only because the thermistor keeps enough resistance to result in enough heat to keep it fairly conductive. This resistance slightly reduces power to the bulb, extending its life somewhat and making it slightly dimmer. DC vs. AC operation As tungsten atoms evaporate from the filament, a very small percentage of them are ionized by the small amounts of short-wave ultraviolet light being radiated by the filament, the electric field around the filament, or by free electrons that escape from the filament by thermionic emission. These tungsten ions are positively charged, and tend to leave the positive end of the filament and are attracted to the negative end of the filament. The result is that light bulbs operated on DC have this specific mechanism that would cause uneven filament evaporation. This mechanism is generally not significant, although it has been reported that light bulbs sometimes have a slight, measurable decrease in lifetime from DC operation as opposed to AC operation. In a few cases, AC operation may shorten the life of the bulb, but this is rare. In rare cases, AC may cause the filament to vibrate enough to significantly shorten its life. In a few other rare cases involving very thin filaments, the filament temperature varies significantly throughout each AC cycle, and the peak filament temperature is significantly higher than the average filament temperature. Ordinarily, one should expect a light bulb's life expectancy to be roughly equal for DC and AC. Why making bulbs last longer often does not pay You may have heard that the life expectancy of a light bulb is roughly inversely proportional to the 12th or 13th power of the applied voltage. And that power consumption is roughly proportional to voltage to the 1.4 to 1.55 power, and that light output is roughly proportional to the 3.1 to 3.4 power of applied voltage. This would make the luminous efficiency roughly proportional to applied voltage to the 1.55 to 2nd power of applied voltage. Now, if a slight reduction in applied voltage results in a slight to moderate loss of efficiency and a major increase in lifetime, how could this cost you more? The answer is in the fact that the electricity consumed by a typical household bulb during its life usually costs many times more than the bulb does. Bulbs are so cheap compared to the electricity consumed by them during their lifetime that it pays to make them more efficient by having the filaments run hot enough to burn out after only several hundred to about a thousand hours or so. Here is an example with actual numbers (using U.S. dollars, in 1996): Suppose you have 10 "standard" 100 watt 120 volt bulbs with a rated lifetime of 750 hours. Such bulbs typically cost around 75 cents in the U.S. The electricity used by all ten of these bulbs is 1 kilowatt, which would typically cost about 9 cents per hour (approximate U.S. average). Over 750 hours, this would cost (on an average) $67.50 for the electricity plus $7.50 for 10 bulbs, or $75. Now, suppose you use these bulbs with 110 volts instead of 120. These bulbs would consume about 87.8 watts instead of 100. However, they would only produce 76 percent of their normal light output (and this is a slightly optimistic figure). To restore the original light output, you need 13 of these bulbs. (And this will fall very slightly short.) Using 13 bulbs that consume 87.8 watts apiece results in a power consumption of 1141 watts. Over 750 hours at 9 cents per KWH, this would cost $77. This is more than the $75 cost of running 10 bulbs at full voltage even if the bulbs never burn out at 110 volts. At 110 volts instead of 120, the life expectancy of the bulbs may be tripled. One third of 13 times 75 cents is about $3.25, which adds to the $77 cost of electricity to result in an average total cost of $80.25 for 750 hours. This example should explain why you often get the most light for the least money using standard bulbs rather than longer-lasting ones. How to minimize lighting costs Higher wattage bulbs tend to be more efficient than lower wattage ones. One reason for this is the fact that thicker filaments can be operated at a higher temperature, which is better for radiating visible light. Another reason is that since higher wattage bulbs would lead you to use fewer bulbs, you buy fewer bulbs and the cost of bulbs becomes less important. To optimize cost effectiveness in this case of higher wattage light bulbs, the filaments are designed to run even hotter to improve energy efficiency to reduce your electricity costs. Smaller bulbs use less electricity apiece, making the cost of the bulb more important. This is why lower wattage bulbs are often designed to last 1500 to a few thousand hours instead of 750 to 1000 hours. Designing the bulbs to last longer reduces their light output and energy efficiency. To minimize your cost of both electricity and bulbs, you should use as few bulbs as possible, using higher wattage bulbs. To get the same amount of light with lower wattage bulbs, you need both more electricity and more bulbs. An even better way to reduce your lighting costs is to use fluorescent, compact fluorescent, or HID (mercury, metal halide, or sodium) lamps since these are 3 to 5 times as efficient as incandescent lamps. Halogen Bulbs The halogen cycle, What are halogen bulbs? A halogen bulb is an ordinary incandescent bulb, with a few modifications. The fill gas includes traces of a halogen, often but not necessarily iodine. The purpose of this halogen is to return evaporated tungsten to the filament. As tungsten evaporates from the filament, it usually condenses on the inner surface of the bulb. The halogen is chemically reactive, and combines with this tungsten deposit on the glass to produce tungsten halides, which evaporate fairly easily. When the tungsten halide reaches the filament, the intense heat of the filament causes the halide to break down, releasing tungsten back to the filament. This process, known as the halogen cycle, extends the life of the filament somewhat. Problems with uneven filament evaporation and uneven deposition of tungsten onto the filament by the halogen cycle do occur, which limits the ability of the halogen cycle to prolong the life of the bulb. However, the halogen cycle keeps the inner surface of the bulb clean. This lets halogen bulbs stay close to full brightness as they age. In order for the halogen cycle to work, the bulb surface must be very hot, generally over 250 degrees Celsius (482 degrees Fahrenheit). The halogen may not adequately vaporize or fail to adequately react with condensed tungsten if the bulb is too cool. This means that the bulb must be small and made of either quartz or a high-strength, heat-resistant grade of glass known as "hard glass". Since the bulb is small and usually fairly strong, the bulb can be filled with gas to a higher pressure than usual. This slows down the evaporation of the filament. In addition, the small size of the bulb sometimes makes it economical to use premium fill gases such as krypton or xenon instead of the cheaper argon. The higher pressure and better fill gases can extend the life of the bulb and/or permit a higher filament temperature that results in higher efficiency. Any use of premium fill gases also results in less heat being conducted from the filament by the fill gas, meaning more energy leaves the filament by radiation, meaning a slight improvement in efficiency. Lifetime and efficiency of halogen bulbs A halogen bulb is often 10 to 20 percent more efficient than an ordinary incandescent bulb of similar voltage, wattage, and life expectancy. Halogen bulbs may also have two to three times as long a lifetime as ordinary bulbs, sometimes also with an improvement in efficiency of up to 10 percent. How much the lifetime and efficiency are improved depends largely on whether a premium fill gas (usually krypton, sometimes xenon) or argon is used. Halogen Bulb Failure Modes Halogen bulbs usually fail the same way that ordinary incandescent bulbs do, usually from melting or breakage of a thin spot in an aging filament. Thin spots can develop in the filaments of halogen bulbs, since the filaments can evaporate unevenly and the halogen cycle does not redeposit evaporated tungsten in a perfect, even manner nor always in the parts of the filament that have evaporated the most. However, there are additional failure modes. One failure mode is filament notching or necking. Since the ends of the filament are somewhat cool where the filament is attached to the lead wires, the halogen attacks the filament at these points. The thin spots get hotter, which stops the erosion at these points. However, parts of the filament even closer to the endpoints remain cool and suffer continued erosion. This is not so bad during continuous operation, since the thin spots do not overheat. If this process continues long enough, the thin spots can become weak enough to break from the weight of the filament. One major problem with the "necked" ends of the filament is the fact that they heat up more rapidly than the rest of the filament when the bulb is turned on. The "necks" can overheat and melt or break during the current surge that occurs when the bulb is turned on. Using a "soft-start" device prevents overheating of the "necks", improving the bulb's ability to survive "necking". Soft-start devices will not greatly extend the life of any halogen bulbs that fail due to more normal filament "thin spots" that run excessively hot. Some halogen bulbs may usually burn out due to filament end necking, and some others may usually burn out from thin, hot spots forming in the filament due to uneven filament evaporation/recovery. Therefore, some models may have a significantly extended life from "soft-starting" and some other models may not. It is generally not a good idea to touch halogen bulbs, especially the more compact, hotter-running quartz ones. Organic matter and salts are not good for hot quartz. Organic matter such as grease can carbonize, leaving a dark spot that absorbs radiation from the filament and becomes excessively hot. Salts and alkaline materials (such as ash) can sometimes "leach" into hot quartz, which typically weakens the quartz, since alkali and alkaline earth metal ions are slightly mobile in hot glasses and hot quartz. Contaminants may also cause hot quartz to crystalize, weakening it. Any of these mechanisms can cause the bulb to crack or even violently shatter. If a quartz halogen bulb is touched, it should be cleaned with alcohol to remove any traces of grease. Traces of salt will also be removed if the alcohol has some water in it. Since the hotter-running quartz halogen bulbs could possibly violently shatter, they should only be operated in suitable fully enclosed fixtures. Use of Halogen Bulbs with Dimmers Dimming a halogen bulb, like dimming any other incandescent lamp, greatly slows down the formation of thin spots in the filament due to uneven filament evaporation. However, "necking" or "notching" of the ends of the filament remains a problem. If you dim halogen lamps, you may need "soft-start" devices in order to achieve a major increase in bulb life. Another problem with dimming of halogen lamps is the fact that the halogen cycle works best with the bulb and filament at or near specific optimum temperatures. If the bulb is dimmed, the halogen may fail to "clean" the inner surface of the bulb. Or, tungsten halide that results may fail to return tungsten to the filament. Halogen bulbs have sometimes been known to do strange and scary things when greatly dimmed. Halogen bulbs should work normally at voltages as low as 90 percent of what they were designed for. If the bulb is in an enclosure that conserves heat and a "soft-start" device is used, it will probably work well at even lower voltages, such as 80 percent or possibly 70 percent of its rated voltage. However, do not expect a major life extension unless soft-starting is used. Even with soft-starting, do not expect to more than double or possibly triple the life of any halogen bulb already rated to last 2,000 hours or more. Even with soft starting, the life of these bulbs will probably not continue to improve much as voltage is reduced to less than about 90 percent of the bulb's voltage rating. Dimmers can be used as soft-start devices to extend the life of any particular halogen bulbs that usually fail from "necking" of the ends of the filament. The bulb can be warmed up over a period of a couple of seconds to avoid overheating of the "necked" parts of the filament due to the current surge that occurs if full voltage is applied to a cold filament. Once the bulb survives starting, it is operated at full power or whatever power level optimizes the halogen cycle (usually near full power) The dimmer may be both "soft-starting" the bulb and operating it at slightly reduced power, a combination that often improves the life of halogen bulbs. Many dimmers cause some reduction in power to the bulb even when they are set to maximum. (A suggestion from someone who starts expensive medical lamps by turning up a dimmer and reports major success in extending the life of expensive special bulbs from doing this.) Ultraviolet from Halogen Bulbs There is some common concern about the ultraviolet output of halogen bulbs, since they operate at high filament temperatures and the bulbs are made of quartz instead of glass. However, the filament temperature of halogen bulbs rated to last 2,000 hours or more is only slightly greater than that of standard incandescent lamps, and the UV output is only slightly higher. Halogen fixtures typically have a glass or plastic shield to confine any possible bulb explosions, and these shields absorb the small traces of shortwave and mediumwave UV that gets through the quartz bulb. Higher temperature photographic and projection bulbs are different. The much higher filament temperature of shorter life bulbs results in possibly significant hazardous UV. For maximum safety, use these bulbs in fixtures or equipment designed to take these bulbs, and in a manner consistent with the fixture or equipment instructions. For those who want to take special precautions against UV, a UV blocking clear filter gel such as the GAM no. 1510 or Rosco "UV Filter" (03114) may be a practical solution. This filter gel withstands use moderately close to halogen lamps and withstands heat to maybe 100 to 150 Celsius or so. This filter gel can be placed immediately outside the glass shield of most fixtures, although the tubular shield in many popular 300 watt torchiere lamps gets too hot for the filter gel. The GAM 1510 and Rosco "UV Filter" is available at some theatrical supply shops. Written by Don Klipstein (Jr). Back to Don's lighting index page. Back to Don's home page Sam's and Don's D-Lamp FAQ Gas Discharge Lamps, Ballasts, and Fixtures Principles of Operation, Circuits, Troubleshooting, Repair Version 1.35 Copyright (C) 1996,1997,1998,1999 Samuel M. Goldwasser Donald L. Klipstein --- All Rights Reserved --- Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: This notice is included in its entirety at the beginning. There is no charge except to cover the costs of copying. Introduction Gas discharge lamp basics The use of electrically excited gas discharges significantly predates the invention of the incandescent lamp. Physics labs of yesteryear as well as today have use of a variety of gas filled tubes used for numerous purposes involving light generation including spectroscopy, materials analysis, studies of gas dynamics, and laser pumping. Look through any scientific supply catalog and you will see many different types of gas filled tubes in all shapes and sizes. Gas discharge lamps are used in virtually all areas of modern lighting technology including common fluorescent lighting for home and office - and LCD backlights for laptop computers, high intensity discharge lamps for very efficient area lighting, neon and other miniature indicator lamps, germicidal and tanning lamps, neon signs, photographic electronic flashes and strobes, arc lamps for industry and A/V projectors, and many more. Gas discharge automotive headlights are on the way - see the section: "HID automotive headlights". Because of the unusual appearance of the light from gas discharge tubes, quacks and con artists also have used and are using this technology as part of expensive useless devices for everything from curing cancer to contacting the dead. Unlike incandescent lamps, gas discharge lamps have no filament and do not produce light as a result of something solid getting hot (though heat may be a byproduct). Rather, the atoms or molecules of the gas inside a glass, quartz, or translucent ceramic tube, are ionized by an electric current through the gas or a radio frequency or microwave field in proximity to the tube. This results in the generation of light - usually either visible or ultraviolet (UV). The color depends on both the mixture of gasses or other materials inside the tube as well as the pressure and type and amount of the electric current or RF power. (At the present time, this document only deals with directly excited gas discharge lamps where an AC or DC electric current flows through the gas.) Fluorescent lamps are a special class of gas discharge lamps where the electric current produces mostly invisible UV light which is turned into visible light by a special phosphor coating on the interior of the tube. See: Fluorescent Lamps, Ballasts, and Fixtures for more info. The remainder of this document discusses two classes of gas discharge lamps: low pressure 'neon' tubes used in signs and displays and high intensity discharge lamps used for very efficient area and directional lighting. Safely Working with Gas Discharge Lamps and Fixtures Fixtures for gas discharge lamps may use up to 30,000 V while starting depending on technology. And, they are often not isolated from the power line. Neon signs are powered by transformers or electronic ballasts producing up to 15,000 V or more. Thus, the only safe way to work with these is to assume that they are potentially lethal and treat them with respect. Hazards include: Electric shock. There is usually little need to probe a live fixture. Most problems can be identified by inspection or with an ohmmeter or continuity tester when unplugged. Discharge lamps and fixtures using iron ballasts are basically pretty inert when unplugged. Even if there are small capacitors inside the ballast(s) or for RFI prevention, these are not likely to bite. However, you do have to remember to unplug them before touching anything! Neon signs using iron transformers are also inert when unpowered - just make sure they are off and unplugged before touching anything! However, those using electronic ballasts can have some nasty charged capacitors so avoid going inside the ballast module and it won't hurt to check between its outputs with a voltmeter before touching anything. Troubleshooting the electronic ballast module is similar to that of a switchmode power supply. See the document: Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies The pulse starters of some high intensity discharge lamps may produce up to 30 kV during the starting process. Obviously, contact with this voltage should be avoided keeping in mind that 30 kV can jump over an inch to anyplace it wants! Nasty chemicals: Various toxic substances may be present inside high pressure discharge lamps (sodium and mercury) and neon signs (some phosphors). Contact with these substances should be avoided. If a lamp breaks, clean up the mess and dispose of it properly and promptly. Of course, don't go out of your way to get cut on the broken glass! WARNING: Metallic sodium reacts with water to produce hydrogen gas, an explosive. However, it is unlikely that the inner tube of a sodium vapor lamp would break by accident. Ultra-Violet (UV) light: High intensity discharge lamps generate substantial UV internally, often the particularly nasty UV-B variety. Unless designed to generate UV (for medicinal purposes, photoengraving, or whatever), the short wave radiation will be blocked by the outer glass envelope and/or phosphor coating. However, should the outer envelope break or be removed, the lamp will still operate (at least for a while - some have a means of disabling themselves after a few hours or less of exposure to air). DO NOT operate such a lamp preferably at all but if you do, at least take appropriate precautions to avoid any exposure to the UV radiation. And take care around sharp sheet metal! Neon Technology Neon Lights and Signs Neon technology has been around for many years providing the distinctive bright glowing signs of commerce of all kinds before the use of colored plastics became commonplace. Neon tubes have electrodes sealed in at each end. For use in signs, they are formed using the glass blower's skill in the shape of letters, words, or graphics. Black paint is used to block off areas to be dark. They are evacuated, backfilled, heated (bombarded - usually by a discharge through the tube at a very high current) to drive off any impurities, evacuated and then backfilled with a variety of low pressure gasses. Neon is the most widely known with its characteristic red-orange glow. Neon may be combined with an internal phosphor coating (like a fluorescent tube) to utilize neon's weak short-wave UV emissions. A green-emitting phosphor combines with neon's red-orange glow to make a less-red shade of orange. A blue-emitting phosphor may be used to result in a hot-pink color. Neon may be used in tubing made of red glass to produce a deep red color. Other colors are usually produced by tubing containing argon and mercury vapor. The mercury is the active ingredient, the argon produces negligible radiation of any kind but is important for the "neon" tubing to work. Clear tubing with mercury/argon glows a characteristic light blue color. Such tubing is often phosphor-coated on the inside, to utilize the major short-wave UV emission of low-pressure mercury. In this way, much of the "neon" tubes in use are a kind of fluorescent lamp. Phosphor-coated tubing with mercury can glow blue, blue-green, slightly white-ish green, light yellow, bright pink, light purple, or white. Use of mercury vapor with colored tubing (with or without phosphors) can provide a lime-green or deep blue or deep violet-blue. Nowadays, nearly all "neon" tubing contains neon or mercury vapor (with argon), whether with or without phosphors and/or colored glass. Well in the past, various colors were obtained (generally at reduced efficiency) by using different gases. For example, helium can produce a white-ish orange light in shorter length, smaller diameter tubing. Hydrogen in this case makes a lavender-hot-pink color. These gases glow more dimly with duller color shades in larger tubing. Krypton makes a dull greenish color. Argon makes a dimmish purple color. Nitrogen (generally in shorter length tubing) makes a grayish purple-pink color. Xenon, which is expensive, generally glows with a dim bluish gray color, along with the glass tubing giving a slight dim blue fluorescence from very short wave UV from the xenon discharge. Krypton also often causes a dim blue glass fluorescence. For general information on neon signs and technology including a neon FAQ, see: The Internet's Neon Shop Power Supplies for Neon Extremely high voltage power supplies are used to power neon signs. In the past, this was most often provided by a special current limited HV line transformer called a neon sign or luminous tube transformer. The output is typically 6,000 to 15,000 VAC at 15 to 60 mA. One such unit can power 10s of feet of tubing. This transformer acts as its own ballast providing the high voltage needed for starting and limiting the running current as well. Warning: the output of these transformers can be lethal since even the limited current availability is relatively high. As with everything else, the newest neon sign power supplies use an electronic AC-AC inverter greatly reducing the size and weight (and presumably cost as well) of these power supplies by eliminating the large heavy iron transformer. Small neon lamps inside high-tech phones and such also use solid state inverters to provide the more modest voltage required for these devices. Neon Sign Installation (From: Clive Mitchell (clive@emanator.co.uk)). The voltage required to light a run of neon tube is variable according to diameter, gas type, pressure and number of tubes in circuit. For a 15 kV transformer and neon gas you could run: 33 feet of 10 mm tube, 45 feet of 12 mm tube, 60 feet of 15 mm tube, 78 feet of 20 mm tube, 102 feet of 25 mm tube. Deduct one foot of tube for every pair of electrodes (tube section). These figures are based on a chart in "Neon Techniques And Handling" which is the traditional neon reference. The larger the diameter of the tube, the lower the voltage required, and the dimmer it will be. Transformers come with different current ratings. For larger diameter tubes, you can increase brightness by using a higher current. Don't attempt to run too much tube on a transformer, since it can cause breakdown of the insulation and destroy the transformer. Don't attempt to run too little tube on a transformer, since it can cause overheating and burn-out. It is absolutely imperative that proper neon sign cabling and insulators are used, and that all local regulations are strictly followed. If you are intending to work with neon tubing, you should learn as much as possible first, since neon poses both a shock and serious fire risk if installed incorrectly. The lengths quoted above may vary according to the transformer you use. The transformer manufacturers usually provide their own loading charts on request. Anyone using this information does so at their own risk, and I cannot be held responsible for any horrible smouldering deaths experienced by incompetent dabblers, etc. (From: Kenny Greenberg (kenny@neonshop.com)). The neon circuit is not so simple. In a standard AC circuit neon acts like a diac - high breakover voltage followed by fast drop in resistance. Neon sign transformers are designed to 'leak' and thus self-regulate. You have a combined resistive and reactive circuit. But take heart, it's all been figured out. :-) There are a few variables: A 'purely' neon filled tube (generally in the red range) has a higher voltage requirement than an argon-mercury tube (whose discharge is usually providing UV for phosphor with a wide range of colors. The voltage requirement varies inversely with the tubing diameter. That is large diameters of a lower voltage requirement than small diameters. The voltage requirement varies directly with tubing length. The number of units (or pairs of electrodes) increases the voltage requirement because the electrodes have a voltage drop. Wiring methods and length will also contribute to the formula but that's a whole 'nuther discussion. You can download a free Neon Voltage Calculator for Windows. An old tech method for determining the voltage requirement is to use a Variac on a large neon transformer. Bring the voltage down to where the neon just flickers. This should be at a point approximately 78% of the required voltage. A better way involves using a milliameter to measure open circuit and closed circuit current and an rms voltmeter to measure actual operating voltage. Problems With Neon These fall into two categories: Power supply - like fluorescent ballasts, the high voltage transformers can fail resulting in reduced (and inadequate) voltage or no power at all. Since they are already current limited, overheating may not result and any fuse or circuit breaker may be unaffected. The use of a proper (for safety if nothing else) high voltage meter can easily identify a bad transformer. If a high voltage probe is not available, position (with power off!) the ends of well insulated wires connected to the outputs of the transformer a fraction of an inch apart (about 1/32" per 1,000 V of transformer rating) and apply the power from a safe distance. If a hot arc results, the transformer is likely good (at least when cold). Neon tubes - these may lose their ability to sustain a stable discharge over time as a result of contamination, gas leakage, or electrode damage (either from normal wear or due to excessive current). Check for obvious damage such as a cracked tube or cracked seals around the electrodes or badly deteriorated electrodes. A previously working tube that now will not strike or maintain a stable discharge on a known good transformer will need to be replaced or rebuilt. Comments on Little Neon Bulbs and Tubes The comments below relate to the little neon bulbs used as indicators, for voltage regulation or limiting, and other applications in all sorts of electronic equipment. (From: Mark Kinsler (kinsler@frognet.net).) Neon lamps can be used for voltage limiters and oscillator elements and just about anywhere else that a non-linear element is needed. The tremolo circuit in the classic Fender guitar amplifier uses a neon lamp relaxation oscillator. The neon lamp is heat-shrinked to a CdS photocell in the volume control circuit. Less well-known is the fact that you can make a pretty reasonable computer logic element out of them: I believe that this was tried sometime in the 1940's. Another cool use is as a radiation sensor: you bias the lamp so that it almost turns on, after which any incident radiation: radio waves (as in police radar), light, or gamma radiation will kick the lamp on. There were various circuits in the 1950's that used neon lamps to detect uranium, fight nuclear destruction, or escape the newly-developed police radar guns. And finally, there's the mystery elevator button. Again, you bias the lamp so that it almost, but not quite, turns on. If you enclose the lamp properly, it'll stay off until you touch it. The electric field variation from your touch will turn the thing on, and it'll stay on. Such lamps are used in some self-service elevators: once the lamp is fired, the low voltage across it is sensed by the ancient logic circuits of the elevator controller and it'll send the elevator to the appropriate floor. These were a lot of fun in the 1960's. I think the controllers used vacuum tubes. The problem with neon lamps is that they're not so reliable. Their turn-on voltage isn't particularly stable. This means that oscillators have a tendency to drift as the lamps age or when ambient radiation changes. I suspect that the computers are slow and cranky, and the radiation detector isn't anything you'd wish to stake your life or drivers' license on. Still, they're great fun, and I have a fine time with them. One other use: hang a neon lamp across a telephone line to detect the ring signal. Place it in series with a piezo beeper, and you've got a reliable telephone ringer. High Intensity discharge Lamps High Intensity Discharge (HID) Lamp Technology These have been used for a long time in street, stadium, and factory lighting. More recently, smaller sizes have become available for home yard and crime prevention applications. Like other gas discharge lamps, these types require a special fixture and ballast for each type and wattage. Unlike fluorescents, however, they also require a warmup period. There are three popular types: High pressure mercury vapor lamps contain an internal arc tube made of quartz enclosed in an outer glass envelope. A small amount of metallic (liquid) mercury is sealed in an argon gas fill inside the quartz tube. After the warmup period, the arc emits both visible and invisible (UV) light. High pressure mercury vapor lamps (without color correction) produce a blue-white light directly from their discharge arc. Phosphors similar to those used for fluorescent lamps can be used to give these a color closer to natural light. (Without this color correction, people tend to look like cadavers). Mercury vapor lamps have the longest life of this class of bulbs - 10,000 to 24,000 hours. The technology was first introduced in 1934 and was the first of the commercially viable HID lamps. Metal halide lamps are constructed along similar lines to mercury vapor lamps. However, in addition to the mercury and argon, various metal halides are included in the gas fill. The most popular combination is sodium iodide and scandium iodide. A few versions of this lamp have lithium iodide as well. A much less common version has sodium iodide, thallium iodide, and indium iodide. The use of these compounds increases the luminous efficiency and results in a more pleasing color balance than the raw arc of the mercury vapor lamp. Thus, no phosphor is needed to produce a color approaching that of a cool white fluorescent lamp with more green and yellow than a mercury vapor lamp (without correction). Some metal halide lamps have a phosphor that adds some orange-ish red light, but not much, since the metal halide arc does not emit much UV. High pressure sodium vapor lamps contain an internal arc tube made of a translucent ceramic material (a form of aluminum oxide known as "polycrystalline alumina"). Glass and quartz cannot be used since they cannot maintain structural strength at the high temperatures (up to 1300 degrees C) encountered here, and hot sodium chemically attacks quartz and glass. Like other HID lamps, the arc tube is enclosed in an outer glass envelope. A small amount of metallic (solid) sodium in addition to mercury is sealed in a xenon gas fill inside the ceramic arc tube. Some versions of this lamp use a neon-argon mixture instead of xenon. Basic operation is otherwise similar to mercury or metal halide lamps. High pressure sodium vapor lamps produce an orange-white light and have a luminous efficiency much higher than mercury or metal halide lamps. Since hot liquid sodium often eventually leaches through things and can get lost this way, sodium lamps have a surplus of sodium in them. Proper lamp operation depends on the sodium reservoir being within a proper temperature range. Mercury vapor lamps are roughly as efficient as fluorescent lamps. Metal halide lamps are much more efficient, generally around 50 to 75 percent more efficient than fluorescent lamps. High pressure sodium lamps are roughly twice as efficient as fluorescent lamps. Unlike fluorescent lamps, HID lamps will give full light output over a wide range of temperatures. This often makes HID lamps more suitable than fluorescent lamps for outdoor use. When cold, the metallic mercury or sodium in the arc tube is in its normal state (liquid or solid) at room temperature. During the starting process, a low pressure discharge is established in the gases. This produces very little light but heats the metal contained inside the arc tube and gradually vaporizes it. As this happens, the pressure increases and light starts being produced by the discharge through the high pressure metal vapor. A quite noticeable transition period occurs when the light output increases dramatically over a period of a minute or more. The entire warmup process may require up to 10 minutes, but typically takes 3 to 5 minutes. A hot lamp cannot be restarted until it has cooled since the voltage needed to restrike the arc is too high for the normal AC line/ballast combination to provide. Problems With High Intensity Discharge Lamps While HID lamps have a very long life compared to incandescents (up to 24,000 hours), they do fail. The ballasts can also go bad. In addition, their light output falls off gradually as they age. For some types, light output may drop to half its original value towards the end of their life. A lamp which is cycling - starting, warming up, then turning itself off - is probably overheating due to a bad bulb or ballast. A thermal protector is probably shutting down the fixture to protect it or the arc is being extinguished on its own. However, make sure that it is not something trivial like a photoelectric switch that is seeing the light from the lamp reflected from a white wall or fence and turning the fixture off once the (reflected) light intensity becomes great enough! Sodium lamps sometimes "cycle" when they have aged greatly. The arc tube's discolorations absorb light from the arc, causing the arc tube to overheat, the sodium vapor pressure becomes excessive, and the arc cannot be maintained. If a sodium lamp "cycles", the first suspect is an aging bulb which should be replaced. Sodium lamp "cycling" used to be very common, but in recent years the lamp manufacturers have been making sodium lamps that are less prone to cycling. If you have more than one fixture which uses **identical** bulbs, swapping the bulbs should be the first test. If the problem remains with the fixture, then its ballast or other circuitry is probably bad. Don't be tempted to swap bulbs between non-identical fixtures even if they fit unless the bulb types are the same. Warning: do not operate an HID lamp if the outer glass envelope is cracked or broken. First, this is dangerous because the extremely hot arc tube can quite literally explode with unfortunate consequences. In addition, the mercury arc produces substantial amounts of short wave UV which is extremely hazardous to anything living. The outer glass normally blocks most of this from escaping. Some lamps are actually designed with fusable links that will open after some specified number of hours should air enter the outer envelope. Thus, an undetected breakage will result in the lamp dying on its own relatively quickly. Troubleshooting a Discharge Lamp Fixture (From: Greg Anderson (a3a30878@bc.sympatico.ca).) The following applies directly to high pressure sodium lamps. It may also also be used for metal halide and mercury vapour lamp problems as long as references to the starter are ignored. (Metal halide and mercury vapour lamps do not have starters, except for "instant re-light" metal hhalide lamps.) The starter produces about 2 to 5 kV spikes to ionize the gas in the lamp. The starter normally has a triac across the ballast and a diac trigger cct. When open cct voltage is across the lamp, the diac fires the triac to short the ballast, the triac then opens. This "kick" produces the voltage spike. Once the gas ionizes, the lamp impedance drops then gradually increases as the lamp warms up. The lamp running voltage is about 1/2 of the open cct voltage With the lamp removed and power on, you can normally hear a good starter "ticking". The open cct voltage is stamped on the ballast and is between about 150 and 350 Vac, depending on lamp wattage and ballast. Also, a capacitor is often connected in series with lamp to improve peaking and ballast action. Steps to follow: Bypass the photo cell - It may be bad Check connections - water, salt, and bird poop are not good for wiring Check the capacitor, if installed - normally they blow-up when bad Check for open/shorted ballast. Power up and check for starter "ticking" REMOVE starter from cct and measure open cct volts Check/Replace lamp Check/replace lamp socket Replace starter Replace complete fixture. Replace electrician. :) Repairing a starter is not economically viable and often proves that electronic devices contain smoke and sometimes fire. Ballasts and Bulbs Should be Matched! HID bulbs generally need specific ballasts, and any given ballast can usually safely and effectively operate only one type or a few types of HID bulbs. The bulb wattage must be matched to the ballast. A smaller bulb will usually be fed a wattage close to what the proper bulb takes, and will generally overheat and may catastrophically fail. Any catastrophic failures may not necessarily happen quickly. A larger bulb will be underpowered, and will operate at reduced efficiency and may have a shortened lifetime. The ballast may also overheat from prolonged operation with an oversized bulb that fails to warm up. See The Discharge Lamp Mechanics Document (rather technical) for why it can be bad to underpower an arc discharge lamp. Even if the ballast and bulb wattages match, substitutions can be limited by various factors including but not limited to different operating voltages for different bulbs. Examples are: Pulse-start sodium lamps often have a slightly lower operating voltage than metal halide and mercury lamps of the same wattage, and ballasts for these sodium bulbs provide slightly more current than mercury and metal halide ballasts for the same wattage would. The higher current provided by the pulse-start sodium ballast can overheat mercury and metal halide lamps. Mercury and metal halide lamps may also "cycle" on and off in lower voltage sodium ballasts, such as many 50 to 100 watt ones. Metal halide lamps have an operating voltage close to that of mercury lamps in many wattages, but have stricter tolerances for wattage and current waveform. Metal halides also usually need a higher starting voltage. Most metal halide lamps 100 watts or smaller require a high voltage starting pulse around or even over 1,000 volts. 175 to 400 watt metal halide lamp ballasts can power mercury lamps of the same wattage, but the reverse is not recommended. Mercury lamps 50 to 100 watts will work on metal halide ballasts, but hot restriking of mercury lamps 100 watts or smaller on metal halide lamps may be hard on the mercury lamp since the starting pulse can force current through cold electrodes and the starting resistor inside the mercury lamp. 1,000 watt mercury lamps come in two operating voltages, one of which is OK for 1,000 watt metal halide ballasts. A few wattages of pulse-start sodium (150 watts?) come in two voltages. A low voltage lamp in a high voltage ballast will be underpowered, resulting in reduced efficiency, possible reduced lamp life, and possible ballast overheating. A high voltage lamp in a low voltage ballast will usually cycle on and off, operate erratically, or possibly overheat. This will usually result in greatly reduced lamp life in any case. One class of sodium lamps is made to work in mercury fixtures, but these only work properly with some mercury ballasts, namely: 'Reactor' (plain inductor) ballasts on 230 to 277 volt lines. 'High leakage reactance autotransformer' ballasts, preferably with an open circuit voltage around 230 to 277 volts. NOT 'lead', 'lead-peak' nor any metal halide ballast! These sodium lamps may suffer poor power regulation and accelerated aging in the wrong mercury ballasts, especially after some normal aging changes their electrical characteristics. Also, these lamps may overheat and will probably have shortened life with pulse-start sodium ballasts. Many sodium lamps require a high voltage starting pulse provided only by ballasts made to power such lamps. Operation of Discharge Lamps on DC Sometimes, one may want to run a discharge lamp on DC. There are two possible reasons: Only DC power is available. To reduce flicker. Sometimes, the lamp performs differently for electricity flowing in one direction than the other. In addition, the positive and negative ends of the arc can make different amounts of light, resulting in a flicker rate equal to the AC frequency rather than twice the AC frequency. However, end flicker is usually not significant. In HID lamps, the total arc size is generally small. Only if the fixture has a reflector that causes some areas to receive light from only one end of the arc should end flicker be significant. In most multi-tube fluorescent fixtures, the tubes are usually in series pairs with the two tubes in any pair oriented in opposite directions. This generally reduces end flicker effects, especially in fixtures with diffusing lenses. Bulbs should perform close enough to identically in both directions, unless the bulb is near the end of its life. In such a case, one electrode deteriorates enough to affect performance before the other does. However, this generally indicates a need to replace the bulb rather than to attempt to make it flicker less. If you want to rectify the AC to provide the bulb with DC, use a bridge rectifier after the ballast. Most ballasts, including all "iron" types, require AC of the proper voltage and frequency to work. Do this only if only two wires feed the bulb. Otherwise, diodes in the bridge rectifier may short parts of the ballast to each other, at least for half the AC cycle. Problems can also occur with fluorescent ballasts with filament windings. Only fully isolated filament windings or separate filament transformers should be used if you rectify the output of a ballast with filament windings. Also, the bridge rectifier must withstand the peak voltage provided by the ballast. If the power supply is DC of adequate voltage, you need a resistor ballast or an electronic ballast specifically designed to run your lamp from the available DC voltage. "Iron" ballasts only limit current when used with AC. Preheat fluorescent lamps operated from DC supplies and without special ballasts need both the usual "iron" ballast to provide the starting "kick" and a resistor to limit current. In addition, most discharge lamps are only partially compatible with DC, and some are not compatible at all. Mercury vapor and fluorescent lamps generally work on DC. However, the life may be shortened somewhat by uneven electrode wear. Fluorescent lamps may get dim at one end with DC. Since the mercury vapor ionizes more easily than the argon, some of it exists as positive ions. This can cause the mercury to be pulled to the negative end of the tube, resulting in a mercury shortage at the positive end. This is more of a problem with longer length and smaller diameter tubes. Some fluorescent fixtures made for use where the power available is DC have special switches to reverse polarity every time the fixture is started. This balances electrode wear and reduces mercury distribution problems. Mercury vapor lamps generally work OK with DC, but some may only reliably work properly if the tip of the base is negative and the shell of the base is positive. This is because the starting electrode does its job best when it is positive. In addition, if the nearby main electrode is positive, it may cause a thin film of metal condensation that shorts the starting electrode to the nearby main electrode. This may make some brands, models, and sizes of mercury lamps unable to start after some use. The negative main electrode will not release as much vaporized electrode material, since the electrode material easily forms positive ions making the electrode material vapor tend to condense on the electrode rather than condense on nearby parts of the arc tube. Metal halide and sodium lamps should not get DC. Use these only with ballasts that give the bulb AC. In metal halide lamps, ions from the molten halide salts can leach into hot quartz in the presence of a DC electric field. This can cause strains in the quartz arc tube. At the ends of the arc tube, electrolysis may occur, releasing chemically reactive halide salt components that can damage the arc tube or the electrodes. The arc tube may crack as a result. There are a few specialized metal halide lamps that are made to work on DC. These often have asymmetrical electrodes and/or short arc lengths. These lamps often also must be operated only in specific positions, and only with the type of current they were designed for in order to achieve the proper distribution of active ingredients within the arc tube and to achieve proper electrode usage. For example, some of these lamps may go wrong in some way or another with AC. In high pressure sodium lamps, which contain both sodium and mercury, the sodium forms positive ions more easily than the mercury does and drifts towards the negative electrode. The positive end can go dim from a lack of sodium. In addition, if any part of the arc tube is filled with a mixture containing excessive sodium and a lack of mercury, heat conduction from that part of the arc to the arc tube will increase. Furthermore, the hot arc tube may suffer electrolysis problems over time in the presence of sodium ions and a DC electric field. Low pressure sodium lamps should not get DC for the same reasons. The sodium is likely to drift to the negative end of the arc tube, and hot glass will almost certainly experience destructive electrolysis problems if exposed to hot sodium or sodium ions and a DC electric field. Special purpose HID lamps such as xenon and HMI The usual general purpose HID lamps are mercury vapor, metal halide, and high pressure sodium. You can get these at home centers, although usually only in wattages up to 400 watts. These versions of HID lamps are optimized for high efficiency, long life, and minimized manufacturing cost. However, the arc surface brightness of these lamps is roughly equal to the surface brightness of incandescent lamp filaments and general purpose halogen lamp filaments. For some applications such as endoscopy and movie projection, it is necessary to have a much more concentrated light source. This is where specialized HID lamps such as short arc lamps and HMI lamps come in. Short arc lamps consist of a roughly spherical quartz bulb with two heavy duty electrodes spaced only a few millimeters apart at the tips. The bulb may contain xenon or mercury or both. Mercury short arc lamps have an argon gas fill for the arc to start in. In a short arc lamp, the arc is small and extremely intense. The power input is at least several hundred and more typically a few thousand watts per centimeter of arc length. The operating pressure in the bulb is extremely high - sometimes as low as 20 atmospheres, more typically 50 to over 100 atmospheres. These lamps are an explosion hazard! Mercury short arc lamps are used when a compact, intense source of UV is needed or where one cannot have the high voltage starting pulses needed for xenon short arc lamps. Mercury short arc lamps are slightly more efficient than xenon ones. The pressure in a mercury short arc lamp does not need to be as high for good efficiency as in a xenon one, but is still tremendous. Xenon short arc lamps are more common than mercury ones, since they do not require time to warm up the way mercury lamps do and have a daylight-like spectrum. A disadvantage of xenon is the requirement of a very high voltage starting pulse - sometimes around 30 kilovolts! Xenon short arc lamps are used for movie projection and sometimes for searchlights. Lower wattage ones are used in specialized devices such as endoscopes. HMI lamps are metal halide lamps with a more compact and more intense arc. The arc is larger and less intense than that of a short arc lamp. Typical power input is hundreds of watts per centimeter of arc length, but gets to a few kilowatts per centimeter in the largest ones. HMI lamps are used in some spotlights. They are used in some endoscopes and projection applications where the intensity of the HMI arc is adequate since they cost less and last longer and are more efficient than true short arc lamps. There are all sorts of HMI and similar lamps, including HTI lamps and the lamps used in HID auto headlights. HID Automotive Headlights First there were gas lamps, then there were electric bulbs, then sealed beam, then halogen. Now, get ready for - drum roll please! - high intensity discharge lamps with sophisticated controllers. High-end automobiles from makers like BMW, Porsche, Audi, Lexus, and now Lincoln are coming equipped with novel headlight technology. No doubt, such technology will gradually find its way into mainstream automobiles - as well as other applications for mortals. Among the potential advantages of HID headlights are higher intensity, longer life, superior color, and better directivity: Light intensity - HID lamps are about 3 times as efficient as halogen lamps. Thus, even when the efficiency of the DC-DC converter is taken into consideration, the lower power input can actually result in much brighter headlights than are possible with halogen bulbs. This reduced power also leads to cooler operation and less drain on the battery and alternator. Lifespan - an HID lamp can be expected to last 2,700 hours or more and thus covered under the bumper to bumper warranty for 100,000 miles. As a practical matter, the HID lamp may outlast the automobile. Since warranty replacement of headlights turns out to be a significant expense, there is strong incentive to see this long lived technology take off. Spectral output - the light from the HID lamp is richer in blue (and more like daylight) than halogen bulbs. This turns out to enhance reflectivity of signs and road markings. Beam pattern - the small arc size of the HID lamp permits the optical system to be optimized to direct light more effectively to where it is needed and prevent it from spilling over to where it is not wanted. In order to make this practical - even for a $40,000 Lexus - special DC-DC converter chips have been designed specifically with automotive applications in mind. These, along with a handful of other basic electronic components, implement a complete HID headlight control system. The HID bulb itself is similar in basic design to traditional HID lamps: Two electrodes are sealed in a quartz envelope along with a mix of solids, liquids, and gasses. When cold, these materials are in their native state (at room temperature) but are mostly gases when the lamp is hot. Starting of these lamps may require up to 20 KV to strike an arc but only 50 to 150 V to maintain it. Lamps may be designed to operate on either AC or DC current depending on various factors including the size and shape of the electrodes. A unique set of ballast operating parameters must be matched to each model HID bulb. Of all the problems that had to be addressed for HID headlights to become practical (aside from the cost), the most significant was the warmup time. As noted in the section: "High intensity discharge (HID) lamp technology", common HID lamps require a warmup period of a few minutes before substantially full light output is produced. This is, of course, totally unacceptable for an automotive headlight both for cold start (imagine: "Honey, I have to go cook the headlights") as well as when they need to be blinked. The warmup problem was solved by programming the controller to deliver constant power to the lamp rather than the more common nearly constant current that would be provided by a traditional ballast. With this twist along with a special lamp design, the lamp comes up to at least 75% of full intensity in under 2 seconds. The controller also provides 'hot strike' capability for blinking (recall that HID lamps typically cannot be restarted when hot). Thus, restarting a hot lamp is absolutely instantaneous. While this technology is just beginning to appear, expect inroads (no pun intended) into household, office, store, factory, and other area and work lighting. The combination of high efficiency, long life, desirable spectral characteristics, small size, and solid state reliability should result in many more applications in the near future. The nearly instant starting capability addresses one of the major drawbacks of small HID lamps. If you have some time and money to spare: Check out: OSRAM Sylvania Products Inc. They have a "sample" for sale at $250.00 for one lamp including the 12 VDC electronic ballast. 42 W total power, 35 W light power, 3,200/2,800 lm output (there are two types, D2S and D2R), 2,000 hours rated lifetime, 91/80 lm/W luminous efficacy, 4,250/4,150 K color temperature, 6,500 cd/cm^2 average luminance, 4.2 mm arc length, burning position horizontal +/- 10 deg., luminous flux after 1 sec. = 25%, max. socket temp. = 180 deg C, any errors are mine. Substitution of Metal Halide Lamps? The following was prompted by a request for info on replacing an (expensive) 250 watt metal halide lamp in a video projector with something else. I would not substitute this lamp, for many reasons below: The metal halide lamp requires a ballast. The ballast should only run a 250 watt metal halide lamp of the same arc voltage. You will have to measure the arc voltage yourself after the lamp warms up, and do this without exposing yourself to the nasty UV that some of these things emit but which does not pass through glass. Arc voltages of many specialized metal halide lamps are not widely published and may or may not be available from the lamp manufacturer. WARNING: The strike voltage on these may be several kV which will probably obliterate your multimeter should the arc drop out and attempt to restart while you are measuring it! Either the operating or strike voltage may obliterate you should you come in contact with live terminals! (Special metal halides probably usually only need a couple to a few kV. Xenon metal halide automotive lamps need 6 to 12 kV to strike and 15 to 20 kV for hot restrike. The worst are short arc xenon that may use up to 30 kV or more.) Most metal halide lamps are AC types and some are DC and you can only use AC lamps on AC output ballasts and DC lamps on DC output ballasts. Different metal halide lamps may have different requirements for starting voltage also. If you match arc voltage, AC/DC type, and the ballast will start the lamp, you might be in business but good chance not. Many projector lamps have specific cooling requirements and some have specific burning position requirements. Metal halide lamps may prematurely fail (possibly violently!) if they overheat, in addition to being off-color. If overcooled, they are more like mercury lamps and will be off-color and have reduced light output. In addition, some metal halide lamps have a halogen cycle in them to keep the inner surface of the bulb clean, and that may not work if the lamp is overcooled and not enough of the chemicals in the bulb get vaporized. This could also even make the lamp fail. If you get the alternate lamp to operate satisfactorily, the arc may be in a different location from that of the original lamp. The arc may be of a different shape or size than that of the original lamp. This can affect your projection. Your projection may not get much light or may have illumination of only part of the picture. The arc may have a different color or spectrum, which can affect the color rendering of what's being projected. Metal halide arcs are often not of uniform color, and if the alternate lamp has a less color-uniform arc than the original lamp then your pictures may have strange color tints in them. As for using a halogen instead of metal halide? You will get less light, as well as problems from the filament having a different shape or size than the original metal halide arc does. Most likely, the filament is larger or longer than the arc and this will reduce the percentage of the light being utilized. Should you try a halogen lamp hack, you will almost certainly have to bypass the metal halide ballast. And halogen lamps emit more infrared than metal halide lamps of the same wattage - you might overheat the source of your image (e.g., LCD panel or transparency). I would not recommend substituting a projector lamp for all of these reasons. This should only be tried at your own risk and only by those that are very familiar with all of the characteristics of the lamps in question - including being familiar with burning position requirements, cooling requirements, shape and size of the light-emitting region, etc. Projector lamps in general, and especially specialized HID lamps, should be used only in equipment made specifically to use the particular lamps in question, or by those who know about these things well enough to make their own ballasts and know the other messy things about these lamps. And you may not save much by using a different lamp - specialized metal halide lamps are all expensive. And for anyone shopping for any sort of projector - look into price, availability, and life expectancy of lamps! Low Pressure Sodium Lamps Low pressure sodium lamps are the most efficient visible light sources in common use. These lamps have luminous efficacies as high as 180 lumens per watt. A low pressure sodium lamp consists of a tube made of special sodium-resistant glass containing sodium and a neon-argon gas mixture. Since the tube is rather large and must reach a temperature around 300 degrees Celsius, the tube is bent into a tight U-shape and enclosed in an evacuated outer bulb in order to conserve heat. As an additional heat conservation measure, the inner surface of the outer bulb is coated with a material that reflects infrared but passes visible light. This material has traditionally been tin oxide or indium oxide. The electrodes are coiled tungsten wire coated with thermionically emissive material, and somewhat resemble the electrodes of fluorescent lamps. Unlike most fluorescent lamps, low pressure sodium lamps have only one electrical connection to each electrode and the electrodes cannot be preheated. The gas mixture is a "Penning" mixture, consisting mainly of neon with a small amount of argon. Depending on who you listen to, this mixture is .5 to 2 percent argon, 98 to 99.5 percent neon. More argon-rich mixtures around 98-2 may be favored today since hot glass has some ability to absorb argon from a low pressure electric discharge. Ideally the mixture should be only a few tenths of a percent argon, in order to ionize most easily and do so much more easily than pure neon or pure argon. A significant surplus of sodium is contained in the glass arc tube since the glass may absorb or react with some of the sodium. The sodium vapor pressure is controlled by the temperature of the coolest parts of the arc tube. When the arc tube reaches a proper temperature, further heating is reduced by the lamp's efficiency at producing light instead of heat. The arc tube has dimples in it, which are normally slightly cooler than the rest of the arc tube. This causes the sodium metal to collect in the dimples instead of covering a larger portion of the arc tube and blocking light. The low pressure sodium lamp usually requires 5 to 10 minutes to warm up. The light of low pressure sodium consists almost entirely of the orange-yellow 589.0 and 589.6 nM sodium lines. This light is basically monochromatic orange-yellow. This monochromatic light causes a dramatic lack of color rendition - everything comes out in an orange-yellow version of black-and-white! This can cause some confusion in parking lots since cars become more alike in color. Some basically red and reddish color fluorescent inks, dyes, and paints can fluoresce red to red-orange from the yellow sodium light and these will stand out in sodium light with color differing from that of the sodium light. Another disadvantage of low pressure sodium light is that many objects will look darker than they would with an equal amount of other light. Red, green, and blue objects look dark under low pressure sodium light. Most other sources of light of sodium-like color such as "bug bulbs" have significant red and green output and will render red and green objects at least somewhat normally. Jaan.be - De Vlaamse zoekmachineSite MeterFree Webite Submission

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Halogen lamp

From Wikipedia, the free encyclopedia

A halogen lamp operating in its fitting with the protecting glass removed

A Halogen lamp behind a round UV filter. A separate filter is included with some halogen light fixtures to remove UV light.

Xenon Halogen Lamp (105 W) for replacement purposes with an E27 screw base

A close-up of a halogen lamp

A halogen lamp, also known as a tungsten halogen lamp or quartz iodine lamp, is an incandescent lamp that has a small amount of a halogen such as iodine or bromine added. The combination of the halogen gas and the tungsten filament produces a halogen cycle chemical reaction which redeposits evaporated tungsten back onto the filament, increasing its life and maintaining the clarity of the envelope. Because of this, a halogen lamp can be operated at a higher temperature than a standard gas-filled lamp of similar power and operating life, producing light of a higher luminous efficacy and color temperature. The small size of halogen lamps permits their use in compact optical systems for projectors and illumination.

Contents

1 History

2 Halogen cycle

3 Effect of voltage on performance

4 Spectrum

5 Safety

5.1 Handling precautions

6 Applications

6.1 Automotive

6.2 Architectural

6.3 Home use

6.4 Stage lighting

6.5 Specialized

7 Disposal

8 See also

9 References

History

A carbon filament lamp using chlorine to prevent darkening of the envelope was patented[1] in 1882, and chlorine-filled "NoVak" lamps were marketed in 1892.[2] The use of iodine was proposed in a 1933 patent,[3] which also described the cyclic redeposition of tungsten back onto the filament. In 1959 General Electric patented[3] a practical lamp using iodine.[4]

Halogen cycle

In ordinary incandescent lamps, evaporated tungsten mostly deposits onto the inner surface of the bulb. The halogen sets up a reversible chemical reaction cycle with the tungsten evaporated from the filament. The halogen cycle keeps the bulb clean and the light output remains almost constant throughout life. At moderate temperatures the halogen reacts with the evaporating tungsten, the halide formed being moved around in the inert gas filling. At some time it will reach higher temperature regions, where it dissociates, releasing tungsten and freeing the halogen to repeat the process. The overall bulb envelope temperature must be higher than in conventional incandescent lamps for the reaction to work.

The bulb must be made of fused silica (quartz) or a high-melting-point glass (such as aluminosilicate glass). Since quartz is very strong, the gas pressure can be higher,[5] which reduces the rate of evaporation of the filament, permitting it to run a higher temperature (and so luminous efficacy) for the same average life.

The tungsten released in hotter regions does not generally redeposit where it came from, so the hotter parts of the filament eventually thin out and fail. Regeneration of the filament is also possible with fluorine, but its chemical reactivity is so great that other parts of the lamp are attacked.[6][7]

It is possible to see a live demonstration of the Tungsten-Halogen cycle in this accelerated video.[8] The lamp is equipped with an open tube that permits the halogen gas to be withdrawn and re-introduced as desired. When switched on, the filament is operating in a vacuum. After a few seconds the bulb is observed to blacken; this is caused by tungsten atoms that evaporate from the filament and condense on the bulb wall. Once completely blackened, the halogen gas is re-introduced back into the bulb. It quickly begins to react with the tungsten that has been deposited on the relatively cold bulb wall, and transports it back to the hot filament. The result is that the wall is returned to its original clarity. In this experiment the concentration of halogen gas used is higher than normal so as to achieve the rapid clean-up. In a standard lamp, the speed of the halogen regenerative cycle is much slower, but it operates continuously to prevent the bulb from blackening and thus maintaining a constant light output during lamp life.

Quartz iodine lamps, using elemental iodine, were the first commercial halogen lamps launched by GE in 1959.[9][10] Quite soon, bromine was found to have advantages, but was not used in elemental form. Certain hydrocarbon bromine compounds gave good results.[6][11] The first lamps used only tungsten for filament supports, but some designs use molybdenum — an example being the molybdenum shield in the H4 twin filament headlight for the European Asymmetric Passing Beam.

High temperature filaments emit some energy in the UV region. Small amounts of other elements can be mixed into the quartz, so that the doped quartz (or selective optical coating) blocks harmful UV radiation. Hard glass blocks UV and has been used extensively for the bulbs of car headlights.[12] Alternatively, the halogen lamp can be mounted inside an outer bulb, similar to an ordinary incandescent lamp, which also reduces the risks from the high bulb temperature. Undoped quartz halogen lamps are used in some scientific, medical and dental instruments as a UV-B source.

For a fixed power and life, the luminous efficacy of all incandescent lamps is greatest at a particular design voltage. Halogen lamps made for 12 to 24 volt operation have good light outputs, and the very compact filaments are particularly beneficial for optical control (see picture). The range of MR-16 (50 mm diameter) reflector lamps of 20 W to 50 W were originally conceived for the projection of 8 mm film, but are now widely used for display lighting and in the home. More recently, wider beam versions are available designed for direct use on supply voltages of 120 or 230 V.

Effect of voltage on performance

Tungsten halogen lamps behave in a similar manner to other incandescent lamps when run on a different voltage. However the light output is reported as proportional to , and the luminous efficacy proportional to .[13] The normal relationship regarding the lifetime is that it is proportional to . For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the luminous efficacy would be about 6.5% higher, but would be expected to have only half the rated life.

Halogen lamps are manufactured with enough halogen to match the rate of tungsten evaporation at their design voltage. Increasing the applied voltage increases the rate of evaporation, so at some point there may be insufficient halogen and the lamp goes black. Over-voltage operation is not generally recommended. With a reduced voltage the evaporation is lower and there may be too much halogen, which can lead to abnormal failure. At much lower voltages, the bulb temperature may be too low to support the halogen cycle, but by this time the evaporation rate is too low for the bulb to blacken significantly. There are many situations where halogen lamps are dimmed successfully. However, lamp life may not be extended as much as predicted. The life span on dimming depends on lamp construction, the halogen additive used and whether dimming is normally expected for this type.

Spectrum

Like all incandescent light bulbs, a halogen lamp produces a continuous spectrum of light, from near ultraviolet to deep into the infrared.[14] Since the lamp filament can operate at a higher temperature than a non-halogen lamp, the spectrum is shifted toward blue, producing light with a higher effective color temperature.

Safety

Halogen lamps get hotter than regular incandescent lamps because the heat is concentrated on a smaller envelope surface, and because the surface is closer to the filament. This high temperature is essential to their operation. Because the halogen lamp operates at very high temperatures, it can pose fire and burn hazards. In Australia, numerous house fires each year are attributed to ceiling-mounted halogen downlights.[15][16] The Western Australia Department of Fire and Emergency Services recommends that home owners consider instead using compact fluorescent lamps or light emitting diode lamps because they produce less heat.[17] Some safety codes now require halogen bulbs to be protected by a grid or grille, especially for high power (1–2 kW) bulbs used in theatre, or by the glass and metal housing of the fixture to prevent ignition of draperies or flammable objects in contact with the lamp.

To reduce unintentional ultraviolet (UV) exposure, and to contain hot bulb fragments in the event of explosive bulb failure, general-purpose lamps usually have a UV-absorbing glass filter over or around the bulb. Alternatively, lamp bulbs may be doped or coated to filter out the UV radiation. With adequate filtering, a halogen lamp exposes users to less UV than a standard incandescent lamp producing the same effective level of illumination without filtering.

Handling precautions

A burned out halogen light bulb

Any surface contamination, notably the oil from human fingertips, can damage the quartz envelope when it is heated. Contaminants will create a hot spot on the bulb surface when the lamp is turned on. This extreme, localized heat causes the quartz to change from its vitreous form into a weaker, crystalline form that leaks gas. This weakening may also cause the bulb to form a bubble, weakening it and leading to its explosion.[18] Consequently, manufacturers recommend that quartz lamps should be handled without touching the clear quartz, either by using a clean paper towel or carefully holding the porcelain base. If the quartz is contaminated in any way, it must be thoroughly cleaned with alcohol and dried before use.

Applications

Medical halogen penlight to observe pupillary light reflex

Halogen headlamps are used in many automobiles. Halogen floodlights for outdoor lighting systems as well as for watercraft are also manufactured for commercial and recreational use. They are now also used in desktop lamps.

Tungsten-halogen lamps are frequently used as a near-infrared light source in Infrared spectroscopy.

Halogen lamps were used on the Times Square Ball from 1999 to 2006. However, from 2007 onwards, the halogen lamps were replaced with LED lights. The year numerals that light up when the ball reaches the bottom used halogen lighting for the last time for the 2009 ball drop. It was announced on the Times Square website that the year numerals for the 2010 ball drop would use LED lights.[19]

Automotive

A close-up of a tungsten filament of a halogen car lamp after several hundred hours of use

Main article: Automotive lamp types

Tungsten-halogen lamps are commonly used as the light sources in automobile headlamps.

Architectural

Linear in various sizes and power

R7S: linear halogen lamp measuring 118mm or 78mm. Also known as a double ended halogen lamp.

Dichroic and plain reflector spots. Higher efficiency versions using infrared reflective coating (IRC) technology are 40% more efficient than standard low voltage halogen lamps

Home use

Halogen multifaceted reflector bulbs are widely available. The most common format is MR16, which is available in 10–50 W power ratings (150–800 lumens).[20]

With the help of some companies such as Philips and Osram Sylvania, halogen bulbs have been made for standard household fittings, and can replace banned incandescent light bulbs of low luminous efficacy.[21][22][23]

Tubular lamps with electrical contacts at each end are now being used in standalone lamps and household fixtures. These come in various lengths and wattages (50–300 W).

Stage lighting

Tungsten halogen lamps are used in the majority of theatrical and studio (film and television) fixtures, including Ellipsoidal Reflector Spotlights and Fresnels. PAR Cans are also predominately tungsten halogen.

Specialized

Projection lamps are used in motion-picture and slide projectors for homes and small office or school use. The compact size of the halogen lamp permits a reasonable size for portable projectors, although heat-absorbing filters must be placed between the lamp and the film to prevent melting. Halogen lamps are sometimes used for inspection lights and microscope stage illuminators. Halogen lamps were used for early flat-screen LCD backlighting, but other types of lamps are now used.

Disposal

Halogen lamps do not contain any mercury. General Electric claims that none of the materials making up their halogen lamps would cause the lamps to be classified as hazardous waste.[24]

See also

Bi-pin connector for base designations GY6.35, G8, etc.

FEL lamp

Lamp base for other bases

List of light sources

References

^ US Patent 254780

^ Harold Wallace A Different Kind of Chemistry: A History of Tungsten Halogen Lamps, IEEE Industry Applications Magazine Nov/Dec 2001, p. 11

^ a b US Patent 2883571

^ Raymond Kane, Heinz Sell Revolution in lamps: a chronicle of 50 years of progress (2nd ed.), The Fairmont Press, Inc. 2001 ISBN 0-88173-378-4 page 75

^ Some lamps have as much as 15 times atmospheric pressure when cold, and some lamps increase pressure five-fold at operating temperature. Kane and Sell 2001, page 76–77

^ a b Burgin and Edwards Lighting Research and Technology 1970 2.2. 95–108

^ Schroder Philips Technical Review 1965 26.116

^ http://www.lamptech.co.uk Museum of Electric Lamp Technology

^ Zubler and Mosby Illuminating Engineering 1959 54.734

^ http://home.frognet/~ejcov/newhalogen.html

^ T'Jampens and van der Weijer Philips Technical Review 1966 27.173

^ Burgin Lighting Research and Technology 1984 16. 2 71

^ Neumann Lichtechnik 1969 21 6 63A

^ Tungsten-halogen lamp information at Karl Zeiss Online Campus site (accessed Nov. 2 2010)

^ Thousands at risk from halogen-light death traps at The Sunday Age site (accessed 22 Dec. 2012)

^ Halogen down light fire safety at Fire and Rescue NSW site (accessed 22 Dec. 2012)

^ Downlights at Western Australia Department of Fire and Emergency Services site (accessed 22 Dec. 2012)

^ Kremer, Jonathan Z."Types of Light Bulbs and Their Uses" Megavolt, section "Halogen", Accessed May 26, 2011.

^ "Times Square Alliance - New Year's Eve - 2010 Widgets".

^ "Replace Inefficient MR16 Halogen Lamps with LEDs". Maxim. September 25, 2007.

^ http://www.consumersearch.com/light-bulbs/philips-halogena-energy-saver

^ http://www.lighting.philips.com/us_en/products/halogena/index.php?main=us_en_consumer_lighting&parent=7593748565&id=us_en_products&lang=en

^ http://www.sylvania.com/en-us/products/halogen/Pages/default.aspx

^ http://www.geconsumerandindustrial.com/environmentalinfo/documents/msds/msds_quartzline_lamps.pdf General Electricl Lamp Material Information Sheet

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