- Tungsten Halogen Lamp Definition: A tungsten halogen lamp is defined as a type of incandescent lamp with halogen gas inside, improving efficiency and lifespan.
- Halogen Lamp Construction: These lamps use quartz for the bulb, which is stronger and withstands higher temperatures compared to traditional glass.
- Working Principle: The working principle of a halogen lamp involves a regenerative cycle where evaporated tungsten combines with halogen gas, then redeposits on the filament.
- Gas Mixture Benefits: A mix of halogen gas with nitrogen and argon maintains high pressure inside the bulb, reducing tungsten evaporation.
- Applications and Types: Tungsten halogen lamps are versatile, used in outdoor lighting, theaters, and scientific instruments, available in various shapes and wattages.
In 1958, E.G. Fridrich and E.H. Wiley had has developed Tungsten Halogen Lamp by introducing a halogen gas (basically Iodine) inside the incandescent lamp. Basically, without halogen gas, incandescent lamp filament gradually losses its performance because of its filament evaporation at higher temperature of operation. The evaporated tungsten from the filament of normal incandescent lamp gets deposited inside the bulb surface gradually. Thus lumens get obstructed from its way to come out from the bulb. So the efficacy i.e. lumen/watt of the incandescent lamp goes down gradually. But the insertion of halogen gas into the incandescent lamp overcomes this difficulty in addition to different advantages. Because this inserted halogen gas helps the evaporated tungsten to form tungsten halide which never gets deposited on the inner bulb surface at bulb surface temperature between 500K and 1500K. So the lumens never face obstruction. So Lumen per watt of the lamp does not deteriorate. Again due to insertion of pressurized halogen gas, the rate of evaporation of the filament goes down.
Working Principle of Halogen Lamp
The working principle of halogen lamp is based on regenerative cycle of halogen.
In incandescent lamp due to high temperature tungsten filament gets evaporated during its operation. Due to convectional flow of gas inside the bulb, the evaporated tungsten is transported away from the filament. The wall of the bulb is relatively cool. Hence the evaporated tungsten then is adhered to the inner bulb wall. This is not the case when halogen like iodine is used in the bulb container. The temperature of the filament of the halogen lamp is maintained at about 3300K. Hence here also tungsten will be evaporated from lamp filament. Due to convectional flow of gas inside the bulb, the evaporated tungsten atoms are transported away from the filament to relatively lower temperature zone where they combine with the iodine vapor and form the tungsten iodide. The temperature required for combination of tungsten and iodine is 2000K.
The convectional gas flow inside the bulb moves the tungsten iodide to the cooler wall, which is kept between 500K and 1500K to prevent adhesion. The tungsten iodide then moves back toward the filament. Near the filament, where temperatures exceed 2800K, the tungsten iodide breaks down into tungsten and iodine vapor.
The tungsten atoms then redeposit on the filament, compensating for the evaporated tungsten. They evaporate again due to the high filament temperature and repeat the cycle. This continuous cycle prevents permanent filament evaporation, allowing the filament to maintain a higher temperature than in regular incandescent lamps. This makes Tungsten Halogen Lamps more efficient, with a higher lumen/watt rating, and gives them a longer lifespan and clearer illumination.
Construction of Halogen Lamp
Compared to halogen lamps, incandescent lamps provide only 80% of their lumens at the end of their life due to tungsten deposits on the glass. Halogen lamps, however, maintain over 95% of their lumens. Initially, borosilicate or aluminosilicate glass was used for halogen bulbs due to their high-temperature resistance and low thermal expansion. Nowadays, quartz is preferred for its strength and higher temperature resistance. The quartz bulb must keep its temperature below 1900K while maintaining around 2800K near the filament for the halogen cycle. A mix of halogen gas, nitrogen, and argon maintains high pressure inside the bulb, reducing tungsten evaporation. Modern halogen lamps often use bromine, which is colorless, instead of iodine, which has a purplish tint.
Application of Tungsten halogen lamps
Tungsten halogen lamps can have a number of shapes but they are most often tubular with the filament oriented axially. Again they are available in both double ended and single ended types. Two types are shown below.
Two types are shown below.
Tungsten halogen lamps give correlated color temperature, excellent lumen maintenance and reasonable life. Tungsten halogen lamps are appropriate to be used in outdoor lighting application. Particularly they can be used in the sports lighting, theater, studios and television lighting etc. Their filaments are generally mechanically stable and positioned with higher precision. Tungsten halogen lamps are being used widely as spotlight, film projectors and scientific instruments. Types of Tungsten halogen lamps in the market of low voltage tungsten filament lamps are also available. They are available at 12, 20, 42, 50 and 75 Watts operated between 3000K and 3300K. Their life ranges from 2000 hours to 3500 hours.
As the optical projection equipments the halogen lamps are generally used, in present days, they are being used widely in the display lighting also.
The main part of the tungsten halogen lamp is small tungsten halogen capsule. It is cemented into one piece, all glass reflectors are as the facets for controlling the beam optically. MR-16 lamp has multifaceted reflector with 2 inch diameter. It has slightly higher luminous efficacy than standard voltage incandescent lamps. Their size is smaller also and permit compact fixture.
