The first generation of automotive light source is fueled by fuel (candles, kerosene or acetylene) direct combustion, it can meet the requirements of early lights, but there is a very low luminous efficiency, light intensity, unstable performance, complex operation and other obvious shortcomings.
The second generation car light source is incandescent. In 1879 Edison invented the incandescent lamp, in 1913 the United States first incandescent lamp technology used in the Cadillac car headlamps, car lighting has undergone a revolutionary change, since the car lighting into the electrical age. Then, there have been car mirrors, starters, generators and batteries and other new technologies, 1925 began the car really into the incandescent car lighting era. The 1950s and the emergence of halogen lamps, it quickly became the main light bulb car light bulbs.
The third generation of automotive light is the gas discharge lamp (HID). It has the advantages of high luminous efficiency, high brightness and high reliability, will replace incandescent, halogen lamp as a new type of automotive headlamp light source.
The fourth generation of automotive light is a semiconductor light emitting diode (LED). LED is a semiconductor PN junction diode, when a forward bias is applied to both ends of the PN junction, the PN junction system is excited, the carrier transition from the low energy state to the high energy state, when the high energy state of the unstable carrier back To the low energy state compound, according to the principle of energy conservation, the excess energy will be released in the form of photons, it is the principle of LED electroluminescence. It is not through the heat to make the object temperature and light, is directly converted from electricity to light, which is called cold light. The wavelength of the light depends on the energy difference between the carriers and the difference between the high energy state and the low energy state.