Halogen incandescent lamp

This is essentially the story of my invention of the quartz halogen lamp, the incandescent lamp that does not blacken. It is still my hope that an A-line type, quartz halogen lamp will become the lamp of choice where compact fluorescent lamps are not suitable. 

Tungsten Halogen Lamp - A type of incandescent lamp that contains a halogen gas in the bulb, which reduces the filament evaporation rate increasing the lamp life. The high operating temperature and need for special fixtures limits their use to commercial applications and for use In projector lamps and spotlights. 

Figure 8.19. Principle of the halogen-filled incandescent lamp. This is a case of vapor transport. The tungsten filament can be kept at a very high temperature because evaporating tungsten is returned to the filament at lower temperatures near the bulb wall the evaporated atoms do not deposit on the bulb wall but react to a volatile component that decomposes to tungsten on the filament.

What is the main difference between a halogen lamp and an ordinary incandescent lamp ... 

In applications that require UV radiation, the lamp envelope is made out of undoped quartz. Thus, the lamp becomes a source of UV-B radiation. A typical halogen lamp is designed to run for about 2000 hours, twice as long as a typical incandescent lamp. 

Dittmer G, Niemann U (1981) Heterogeneous reactions and chemical-transport of tungsten with halogens and oxygen under steady-state conditions of incandescent lamps. Philips J Res 36 87-111... 

Type of lamp Incandescent lamps Tungsten halogen High pressure mercury High pressure sodium... 

Small additions of iodine and bromine are used in halogen lamps. The bulbs are small and made of quartz. Vaporized tungsten from the filament forms tungsten iodide/bromide with the gas and this compound reacts with the filament and redeposit tungsten on it. In these types of lamps the filament can have a much higher temperature than in conventional incandescent lamps, 3200 K compared to 2700 K. 

Photochemical halogenations may also be convenient on the laboratory scale. As an example, benzylic bromination is conveniently carried by using HBr/H202 under irradiation with a common incandescent lamp (see Scheme 2.22)[37]. Apropos halides, it may be added that fragmentation of the carbon-halogen bond has been considered above for aromatic derivatives, but is useM also for aliphatic derivatives. A typical example is the photocyclisation of iV-phenyl chloroaceta-mides and Af-arylalkyl chloroacetamides (see Scheme 2.23)[38]. 

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