Halogen lamps are actually a special type of incandescent lamps. The principle is that when a current passes through a resistor, it will generate heat, and when the temperature is high enough, it will emit black body radiation with a wavelength in the visible light frequency band. There are generally two types of halogen lamps: iodine tungsten lamps and bromine tungsten lamps, and the principle is the same. When an incandescent lamp is lit, although the filament temperature does not exceed the melting point and boiling point of tungsten, a small amount of tungsten will still volatilize at high temperature. When the volatilized tungsten atoms meet the cooler bulb shell, they will condense and precipitate, and a black tungsten film will accumulate on the bulb shell over time. This is the reason why the shell of ordinary incandescent lamps turns black after being used for a long time. If some iodine is filled in the bulb, when the bulb is lit, the iodine will volatilize into a gas, and the iodine vapor will react with the colder tungsten to form a low boiling point compound - tungsten iodide, thus making the bulb shell The precipitated tungsten evaporates. Tungsten iodide gas will decompose when exposed to high temperature. When tungsten iodide gas meets the filament, it decomposes, leaving tungsten on the filament, while iodine continues to be free in the form of gas between the filament and the shell, and when it comes to the bulb shell again, it will bond with the shell again Tungsten reaction... In this way, on the one hand, the filament continuously volatilizes tungsten to the bulb shell, and on the other hand, iodine continuously transports tungsten back to the filament, so that the volatilization and consumption speed of the filament is greatly reduced, and the life of the bulb can be extended. Thus, a high-power incandescent lamp, such as 1000 watts, can be made from an iodine-tungsten lamp. If no halogen is added, if the ordinary incandescent lamp achieves such a high power, its life will be very short and it will be difficult to be practical. Halogen lamps have been widely used in automotive lighting.
