Modern vehicles use many different kinds and sizes of lamps.
They all consist of 1 or more filaments which heat up until they glow. The filament material doesn’t burn because most of the air in the bulb has been replaced by inert gases that stop combustion occurring.
The power in watts is often marked on the lamp. The power in watts being consumed by the lamp is found by multiplying the voltage to the lamp, by the current flowing through it.
Incandescent Light Bulb
The incandescent light bulb (archaically known as the electric lamp) uses a glowing wire filament heated to white-hot by electrical resistance, to generate light (a process known as thermal radiation or incandescence). The bulb is the glass enclosure which keeps the filament in a vacuum or low-pressure noble gas, or a halogen gas in the case of quartz-halogen lamps (see below) in order to prevent oxidation of the filament at high temperatures. In Australia and South Africa a light bulb is also called a light globe.
Because of its poor efficiency and yellowish color, it is being gradually replaced in many applications by fluorescent lights, high-intensity discharge lamps, Light-emitting diodes (LEDs), and other devices.
Halogen Lamp
The problem of short bulb life is addressed in the halogen lamp which is filled with a halogen gas such as iodine or bromine. This creates an equilibrium reaction where evaporated filament is chemically re-deposited at the hot-spots, preventing the early failure of the lamp. This allows halogen lamps to be run at higher temperatures which would cause unacceptably low lamp lifetimes in ordinary light bulbs, allowing for greater brightness and efficiency.
Because the lamp envelope must be very hot for this to work, the envelopes are often made of quartz glass instead of ordinary glass, which would soften and flow too much at these temperatures. Thus halogen lamps are sometimes called tungsten halogen lamps and are sometimes called quartz halogen lamps. They were once called quartz iodine lamps.
Perhaps the most significant side effect of using quartz instead of ordinary glass is that the lamp becomes a source of UV-B light, because the quartz is transparent to this spectral range and ordinary glass is not. One consequence is that it is possible to get a sunburn from excess exposure to the light of a quartz halogen lamp. Quartz halogen lamps are used in some scientific instruments as UV-B light sources. To mitigate the negative effects of UV exposure some manufacturers add UV inhibitors to the lamp envelope that effectively filter UV radiation. When this is done correctly, a halogen lamp with UV inhibitors will produce less UV than its standard incandescent counterpart.
Because the quartz is hot, and poses a danger of fire or burns, and because of the risk from UV exposure, these lamps are usually protected by a filter of ordinary glass, which, as noted above, absorbs most of the UV-B light.
The quartz glass can be damaged by residue from fingerprints. These bulbs should be handled without touching the quartz capsule (the actual light bulb). If the quartz capsule is touched, it must be cleaned with rubbing alcohol.
The incandescent light bulb is still widely used in domestic applications, and is the basis of most portable lighting (for instance, some car headlamps and electric torches). Halogen lights have become more common in auto headlights and domestic situations, particularly where light is to be concentrated on a particular point. The fluorescent light, has, however, replaced many applications of the light bulb with its superior life and energy efficiency. LED lights are beginning to see increased home and auto use, replacing incandescent bulbs. Newer headlights are going to high-intensity discharge lighting, such as halogen metal oxide, which look purplish instead of yellowish.
Source: CDX Global & Wikipedia - en.wikipedia.org
