What's the long life of LEDs? That starts with the principle of LED. LED, or light-emitting diode. It is a semi conducting solid-state light-emitting device. It uses solid semiconductor chips as luminescent materials. When positive voltage is applied at both ends, red, yellow, green, green, orange, purple and white light will be emitted directly. Changeable and unreal: LED light source can use the principle of red, green and blue three primary colors to realize multiple changes of color and pattern under the control of computer technology. It is a kind of "dynamic light source" that can be controlled at will.
It can be seen that the diode is mainly driven by the continuous movement of carriers, and there is no aging and burnout phenomenon, so the LED light-emitting life can be very long.
Although LED lighting has the characteristics of energy saving, environmental protection, long life, easy control, maintenance free, etc., it is ironic that we often hear that the life of LED driving power directly affects the LED lighting fixtures and becomes not "long life", which greatly increases the maintenance / use cost; or the energy efficiency conversion ratio of LED lighting fixtures is not due to the low efficiency of driving power. As high as you can imagine, or because the output current ripple is not well controlled, the luminous quality is affected, which greatly reduces the green energy-saving advantage of LED lighting, and even affects the market popularity.
If the failure of power supply and drive is not considered, the life of LED is shown as its light failure, that is to say, when the time is long, the brightness becomes darker and darker until it finally goes out. The 30% decay time is usually defined as its lifetime. So can led life be predicted? The answer is yes.
LED life can also be predicted!
1. LED light attenuation:
Most white LEDs are produced by irradiating yellow phosphor with blue LEDs. There are two main causes of LED light failure. One is the light failure of blue LED. The light failure of blue LED is much faster than that of red, yellow and green LED. Another is the light decay of phosphor, which is very serious at high temperature. Different brands of LED have different light attenuation. Generally, LED manufacturers can provide a set of standard light attenuation curve.
The light decay of LED is related to its junction temperature. The so-called junction temperature is the temperature of semiconductor pn junction. The higher the junction temperature, the earlier the light decay occurs, that is, the shorter the life. It can be seen from the figure that if the junction temperature is 105 degrees, the service life when the brightness is reduced to 70% is only more than 10000 hours, and 20000 hours when the junction temperature is 95 degrees, and 50000 hours when the junction temperature is reduced to 75 degrees, and 90000 hours when the junction temperature is 65 degrees. So the key to prolong life is to reduce junction temperature. However, these data are only suitable for Cree's LEDs. Not suitable for LED of other companies.
When the junction temperature is increased from 115 ℃ to 135 ℃, the service life will be reduced from 50000 hours to 20000 hours. The light decay curve of other companies should be available from the original factory.
2. How to extend the life of LED
The key to prolong its life is to reduce its junction temperature. The key to reduce the junction temperature is to have a good radiator. It can timely release the heat generated by LED. We are not going to discuss how to design the radiator here, but which radiator
The problem of relatively good heat dissipation effect. In fact, this is a junction temperature measurement problem. If we can measure the junction temperature that any kind of radiator can achieve, then we can not only compare the cooling effect of various radiators, but also know the LED life that can be achieved after using this radiator.
It seems that it should be very simple to estimate the life from junction temperature. As long as you look up the curve in Figure 1 below, you can know that the life corresponding to 95 ℃ junction temperature can get the life of LED is 20000 hours. However, this method can be used in indoor LED lamps with certain reliability. If it is used in outdoor LED lamps, especially in high-power LED street lamps, there are many uncertain factors. The biggest problem is that the heat dissipation efficiency of LED street lamp radiator decreases with time. This is due to the accumulation of dust and bird excrement, which reduces the heat dissipation efficiency. Also because there is a strong UV outside, it will reduce the life of LED. UV mainly plays a great role in the aging of epoxy resin. If silica gel is used, it can be improved.