Light produced with a higher temperature filament has more bluish spectrum, which gives an impression of whiter light to human eyes. Higher filament temperature will increase the ratio of visible light, which belongs to rather short wavelength band of emission from a halogen lamp. This results in building up higher gas pressure inside, suppressing tungsten vaporization, thus achieving long life as well as better lumen maintenance performance as shown in the appendix 2. In order to achieve good halogen cycle, halogen lamps have generally much compact bodies (made of quartz to withstand the high temperature) compared with conventional lamps.
#Halogen light free
The free tungsten atom W can deposit itself onto a cold portion of the filament, but the X remains floated in the gas, repeating the process over and over. Since the temperature near the filament exceeds 2000☌, WX2 is disintegrated to W and Xs again. If the temperature at the quartz glass is above 250 ☌, which is over the condensati on temperature of WX2, the molecules can not condensate themselves on the wall, therefore circulate back towards the filament. Tungsten atoms W which have evaporated from the filament combine with halogen vapor to form WX2, which traverse towards the quartz glass wall. Halogen cycle, The appendix 1 illustrates chemical reaction inside a halogen lamp. Halogen lamps do not have this slow deterioration thanks to a chemical process that is called “halogen cycle”. Conventional incandescent lamps lose their light fluxgradually during the operation, due to tungsten vapor accumulation on inner bulb surfaces (blackening phenomenon). Its gas consists of not only inert gas which is commonly use in gas-filled lamp technology, but also small trace of halogen material. These lamps are also used as projection lamps in motion pictures and slide projectors.A halogen lamp is a kind of gas-fillet tungsten filament lamp.
Halogen lamps are also used in stage lighting. They are used as an infrared light source. Halogen lamps were used on the Times Square Ball. Halogen lamps are widely used in automobiles as headlamps. Some applications of the halogen lamps are given below. Halogen lamps have high operating temperature with increased luminous efficiency. Halogen lamps has no blackening of lamp, thus there is no depreciation of lumens output. These lamps produce better color radiation. Halogen lamps have long life, around 2000 to 4000 hours. The primary advantages of the halogen lamps are given as − The halogen lamps can operate at a higher temperature than a standard gas filled incandescent lamp of the similar power rating without loss of its operating life. The use of halogen gas at low pressure in the lamp reduces the uneven evaporation of the filament and darkening of the glass cover. There are two terminal leads connected to the lamp filament for supply the power to the filament. This glass cover of the lamp is filled with an inert gas like argon and nitrogen. The halogen lamp consists of a filament of tungsten metal, which is enclosed in a fused silica quartz glass. The construction of the tungsten halogen lamp is shown in the figure. A major portion, up to 85%, of the light emitted by the halogen lamps lies in the infrared region, around 15% to 20% lies in the visible region and less than 1% lies in the ultraviolet region Construction of Halogen Lamp The halogen lamps have continuous spectral output. The brightness of the emitted light is proportional to the heating temperature. light is produced by heating a solid to a very high temperature. The working of the halogen lamp is based on the principle of thermal radiator, i.e. Also, the halogen cycle prevents the darkening of the lamp envelope by redepositing the tungsten from the inside of the lamp back onto the filament.
This regenerative cycle increases the life span of the filament. The combination of the tungsten filament and the halogen results in a chemical reaction (called regenerative cycle or halogen cycle). The halogen lamp consists of a tungsten filament enclosed in an environment of an inert gas like argon and a small amount of a halogen like bromine or iodine. A halogen lamp or tungsten halogen lamp is an incandescent lamp.
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