Automotive headlights are generally composed of three parts: light bulb, reflector and matching mirror (astigmatism mirror).
1. bulb
The bulbs used in automobile headlights are incandescent bulbs, halogen tungsten bulbs, new high-brightness arc lamps and so on.
(1) Incandescent bulb: its filament is made of tungsten wire (tungsten has a high melting point and strong light). During manufacturing, in order to increase the service life of the bulb, the bulb is filled with an inert gas (nitrogen and its mixture of inert gases). This can reduce the evaporation of tungsten wire, increase the temperature of the filament, and enhance the luminous efficiency. The light from an incandescent bulb has a yellowish tinge.
(2) Tungsten halide lamp: Tungsten halide light bulb is inserted into the inert gas into a certain halide element (such as iodine, chlorine, fluorine, bromine, etc.), using the principle of tungsten halide recycling reaction, that is, the gaseous tungsten evaporating from the filament reacts with the halogen to produce a volatile tungsten halide, which diffuses to the high temperature area near the filament, and is decomposed by heat, so that the tungsten is returned to the filament. The released halogen continues to diffuse and participate in the next cycle reaction, so the cycle continues, thereby preventing the evaporation of tungsten and the blackening of the bulb. Tungsten halogen light bulb size is small, the bulb shell is made of quartz glass with high temperature resistance and high mechanical strength, under the same power, the brightness of tungsten halogen lamp is 1.5 times that of incandescent lamp, and the life is 2 to 3 times longer.
(3) New high-brightness arc lamp: This lamp has no traditional filament in the bulb. Instead, two electrodes are placed inside a quartz tube. The tube is filled with xenon and trace metals (or metal halides), and when there is enough arc voltage on the electrode (5000 ~ 12000V), the gas begins to ionize and conduct electricity. The gas atoms are in an excited state and begin to emit light due to the energy level transition of the electrons. After 0.1s, a small amount of mercury vapor is evaporated between the electrodes, and the power supply is immediately transferred to the mercury vapor arc discharge, and then transferred to the halide arc lamp after the temperature rises. After the light reaches the normal working temperature of the bulb, the power of maintaining the arc discharge is very low (about 35w), so 40% of the electric energy can be saved.
