1 Car lights and requirements
At present, cars are becoming more and more civilian, and have become the main means of transportation. The safety of driving has aroused widespread concern in society. According to incomplete statistics, the mileage of a car at night or under natural light accounts for 25% of the total mileage, while traffic accidents here account for 40% of the total accidents, and more than half of the casualties occur at night. . Therefore, the exterior lights and signal lights are the key components for safe driving of the car, and the following conditions must be met:
(1) The car illuminator lights up without delay, the response time is faster, giving the driver more reaction time.
(2) The illumination is strong, and the driver's field of vision is improved at night or when there is insufficient natural light, and the indication of the external signal light is stronger.
(3) High seismic resistance, high reliability, and avoid accidents caused by lighting failures.
(4) Energy saving, which can effectively reduce the emission of exhaust gas and protect the environment.
(5) Based on the increasingly fierce competition in automobile sales, the design of the lamp should be practical and beautiful.
2 LED becomes a new star in automotive lighting selection
2.1 How LEDs work
The LED is a special diode and is a semiconductor device in which a PN junction is formed by doping or the like. When the diode conduction condition is met, current flows through the LED, releasing energy in the form of light and heat. LED is a current-controlled current-type component, and its luminous intensity is mainly based on the magnitude of the current passed. When it is forward-conducting, its voltage drop is very high, and it has a certain fluctuation range.
Since LEDs do not have infrared and ultraviolet radiation, the energy consumed is almost all thermal energy except for conversion to light energy, and can only be transmitted in the form of heat conduction. Therefore, the junction temperature will gradually increase when the LED is in operation. While the LED is a device with a negative temperature coefficient, the current flowing through the LED will increase with increasing temperature, which creates a positive feedback, causing a further increase in junction temperature. If left uncontrolled, the LED will burn out. The thermal parameters of the LED are closely related to the junction temperature of the PN junction. The relationship between the dominant wavelength and temperature is as follows:
Mp(Tl) = m0(T0)+ 3Tg #0.1nm/°C
It can be seen from the above formula that whenever the junction temperature of the LED rises by 10 ° C, the dominant wavelength (which can be observed by the human eye) drifts to the long wave by 1 nm (1 nm = 10-9 m), resulting in a decrease in the brightness of the LED and a light decay. Therefore, if the individual LEDs are overheated, the uniformity of the LED array illumination will be deteriorated.
2.2 LED significant lighting advantages
LEDs are called new light sources because LEDs have the characteristics of point and solid-state light sources, so they have advantages that other lighting sources cannot match.
(1) The life of LED can reach 100,000 hours theoretically, and the actual life can reach more than 20,000 hours. It is more advantageous than the 1 000 hours of ordinary white light bulbs and 10,000 hours of daylight lamps. replace.
(2) No delay in lighting, faster response time. The LED's startup time is only a few tens of nanoseconds, and the startup time is much shorter than that of incandescent bulbs.
(3) In the case of high light intensity and low natural light visibility, the incidence of automobile accidents is greatly reduced; basically no radiation, belonging to the "green light source".
(4) LED has small footprint, simple structure and high shock resistance. Designers can change the lamp mode at will, so that the car can be diversified to meet different consumer needs.
(5) LED light source is much less affected by voltage changes than incandescent bulbs, showing excellent safety and reliability, while consuming 80% less energy than incandescent lamps with the same efficacy, very energy efficient.
Based on the above advantages, LED can be widely used in automotive lighting, but a single LED can not meet the requirements of automotive lighting intensity, and must be used in series, parallel or series-parallel to form an LED array.
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