How to predict and test the life of LED?

In general, LED can be used for more than 50000 hours, and some manufacturers are promoting their LED to operate for about 100000 hours. The main problem in this area is that LED is not simply no longer operational. Its rated service life can not be calculated by traditional lamps and lanterns. In fact, when testing the life of LED, no one will be waiting for it to stop functioning. However, there are other ways to measure the life of LED. The reason why LED is durable is that it does not produce filament fuses. LED will not stop operation directly, but it will gradually deteriorate over time. It is predicted that high quality LED can maintain more than 60% of the initial lamp brightness after 50000 hours of continuous operation. Assuming that LED has reached its rated service life, it may still be luminous, but the light is very weak.

Without considering the power and driving failures, the life span of LED is characterized by its decay, that is, the longer the time is, the more darker the brightness will be, until finally extinguished. The time of decay of 30% is usually defined as its life. So can the life of LED be predicted?

 1. Light failure of LED
Most white LED is obtained by irradiating yellow phosphor with blue LED. There are two main reasons for LED fading. One is the decay of Blu ray LED itself, and the blue light LED has far more light decay than red light, yellow light and green light LED. Another is the decay of phosphor, and the attenuation of phosphor at high temperature is very serious.

The decay of LED is related to its junction temperature. The so-called junction temperature is the temperature of the semiconductor pn junction. The higher the junction temperature is, the earlier the decay occurs, that is, the shorter the life. If the junction temperature is 105 degrees, the lifetime of the brightness to 70% is only more than 10000 hours, 95 degrees will be 20 thousand hours, and the junction temperature is reduced to 75 degrees, the life will be 50 thousand hours, and 65 degrees can be extended to 90 thousand hours. So the key to prolonging life is to reduce junction temperature. But these data are only suitable for Cree’s LED. It’s not suitable for other companies’ LED. When the junction temperature is increased from 115 to 135, the life will be reduced from 50000 hours to 20000 hours.

2. How can we prolong the life of LED?
The key to prolonging its life is to reduce its junction temperature. The key to lowering the junction temperature is to have good radiator. It is able to send out the heat generated by LED in time.

3. How to predict the life of this lamp.

Judging from the junction temperature, life expectancy should be very simple. You can know that the life of LED can reach 20 thousand hours at the temperature of 95 knots. However, this method for indoor LED lamps and lanterns has certain credibility, if applied to outdoor LED lamps, especially high power LED street lamps, there are many uncertainties. The biggest problem is that the heat dissipation efficiency of the LED Street radiators decreases with time. This is due to the accumulation of dust and bird droppings, resulting in reduced heat dissipation efficiency. Also because there is a strong ultraviolet light outside, it will also reduce the life of LED. Ultraviolet radiation plays an important role in the aging of encapsulated epoxy resin. If silica gel is used, it can be improved. Ultraviolet radiation also has some bad effects on the aging of phosphors, but it is not very serious.

The LEDLM-80PL LED luminous flux maintenance rate and aging life testing system, launched by Shanghai power Shantou, are designed and manufactured according to the CIE and IEC standards such as IES-LM-80, IES-LM-82, TM-21, GB2312-80 and so on. It can record the curve of luminous flux with time and the curve of color parameter changing with time. The life time of LED is calculated by testing the data of light decay for a short time.

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