How Much Does LED Light Know?

LED light decay means that after a period of light, its light strong will be lower than the original light, and the lower part is the LED's light decaying. , Everyone also realizes that an important way to reduce light decay is to improve its heat dissipation. However, the test results of various street lights have been recently tested by the Light Environment Management Center, and the light decay of most street lights cannot meet the requirements of the use. The light decay after 1200 hours of light is 8%, the worst is 26%, and the average is 14%. According to our test results, when the knot temperature is 105 degrees, 14%light decay should also be working 6000 hours. It can be seen that the knot temperature of most street lights is above 105 degrees or more. A considerable part of the company must not agree with such a result, because they think that their radiator is carefully designed. The actual situation may be the same, but the test results cannot be doubted. What's the problem? The editor believes that the radiator may not be designed so badly, but may. But why does the power supply of constant voltage power supply cause light decay? This sounds like a little heavenly. But in fact, there are indeed so serious. Let's start from the beginning! 1. We all know that LED's Viaticity is a diode, and the most important electrical characteristics of the diode are its Vodiat nature. 2. Although the temperature characteristics of LED Voldown characteristics are not the same as that of the average diode, the biggest difference is that its temperature characteristics. In fact, all diodes have the problem of temperature characteristics, but the LED needs special attention to pay special attention. This is because: The working current of high-power LED is relatively large, 1W is 0.35A, 3-5W is 0.7A, 20W is 1.05A, 30W is 1.75A, 50W is 3.5A is 3.5A. However, some people may feel that the positive current of the rectifier diode may also reach such a large value. Because the current light emitting efficiency is still relatively low, most of the input electricity power is converted into heat, so its heating is very high. If the radiator does not do well, the knot temperature will rise very high. The LED is different from the rectifier diode. It is not made of general silicon materials, but it is made of special materials (such as nitride). Therefore, the temperature characteristics of its ambush characteristics are different from the average diode, but to be significantly greater than the average diode. For example, the temperature characteristics of the ambush characteristics of the average diode are -2mv/ C. 3. The problem caused by the increase of the knot temperature After the LED knot temperature rises, the first brought by the light output is reduced. The elevation of the ease caused by the elevation of the knot temperature is negative because the temperature coefficient of the voltano characteristics is negative, which means that the temperature is elevated and the characteristics are left to move. For example, assume that the temperature rises by 50 degrees, then the Fa'an characteristics will move to 200mv to left. The use of constant voltage power supply power supply will increase the positive current of the LED with the increase of the temperature rise. Because the power supply voltage is constant, and the Fa'an characteristics have shifted to the left, the result is that the positive current increases. It can be seen from the Fuan characteristics of Figure 2 that if the constant voltage power supply is powered by 3.3V at room temperature, the forward current current is 350mA; after the knot temperature rises by 50 degrees, the voltano characteristics are left by 0.2V, which is equivalent to the power supply, which is equivalent to the power supply, which is equivalent to the power supply, which is equivalent to the power supply. The voltage rises to 3.5V. At this time, the positive current will increase to 600mA. 4. After the use of the vicious cycle of the temperature increase to increase the vicious cycle of the constant voltage power supply, because the power supply voltage has not changed, the input power of the LED increases to 3.3VX0.6A = 1.98W, which has doubled doubled by doubled. After the knot temperature rises, the light output will decrease, which means that more input power is converted to thermal energy, that is, if the forward current increases at this time, its light output does not increase as it increases, but it will decrease. Therefore, the increase in the positive current at this time will only cause an increase in the knot temperature, and it will not increase the output of the light. Therefore, after increasing the knot temperature, the positive current increases, the knot temperature increases, and the forward current increases, which causes the vicious cycle of the rising temperature of the knot temperature. Conclusion: The use of constant voltage power supply power supply will increase the knot temperature, increase light decay, and shorten life. Therefore, from the previous analysis, we can draw such a conclusion: The use of constant voltage power supply power supply will increase the knot temperature, and the result of increasing the knot temperature is increased by light decay and shortened life span. Assuming that LED is turned on at 25 degrees at room temperature, the knot temperature will rise after booting. Assume that the radiator is designed to rise to 75 degrees, that is, the knot temperature increases by 50 degrees, then the positive current will increase to 600mA to 600mA to 600mA. The total power increased from 1.155W to 1.98W, an increase of 0.825W 0.825W. And the power increased in this part is almost all converted to heat. Assuming that the original LED's luminous efficiency is 30%, that is, the 70%input power (0.8W) is converted to thermal energy to the thermal energy energy. Now there are double thermal energy that need to be dispersed from the radiator. Obviously, this is not considered by the original radiator design. This has increased the knot temperature of LED by 50 degrees to 125 degrees. Let's go back to Figure 1 to see the optical decay curve. The life of 125 degrees of light is almost 1200 hours. Then you can explain why a carefully designed radiator. It is still a lot of light decay and a short life span! Therefore, power supply to LED must be powered by a constant current power supply. After the current is constant, no matter how the temperature changes, the ambush characteristics are moved left, and the current does not change! The knot temperature will not be vicious!