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Why does light depreciation happen and how to deal with it

Jul 19, 2019

Why does light depreciation happen and how to deal with it


The lights are the same as people, and as time goes by, the various functional mechanisms continue to decline, and finally until the decline. No matter what kind of light source the luminaire can't avoid, and this is the light depreciation of the luminaire.


Causes of light depreciation


There are still many controversies about the cause of light decay, and the microscopic mechanism causing the decline is still inconclusive. However, in general, the light decay for LEDs is mainly caused by heat dissipation.


LED is afraid of heat is a well-known thing, LED ideal operating temperature is between -5 ~ 0 °, but this is basically impossible, heat will affect the light decay and life of LED lamps, LED will work About 80% of the electric energy is converted into heat energy, and 20% of the electric energy is converted into light energy. The LED radiator is used to dissipate the heat of the LED. Because the LED chip is working, his own ambient temperature is inversely related to the light output rate. The higher the temperature, the lower the light output rate. When the temperature reaches the maximum temperature of the LED chip, the lamp will break.


In addition, the thermal resistance of the LED chip itself, the influence of silver paste, the heat dissipation effect of the substrate, and the colloid and gold wire are also related to the light decay.


How to solve the light decay of lamps?


In fact, in a strict sense, LED lamps can not avoid light decay. It is a technical problem that the industry cares about urgently, but as long as we understand the heat dissipation method of lamps, we can reduce the light attenuation problem to some extent.


The first thing to understand is the junction temperature?


The junction temperature is the operating temperature of the PN junction of the semiconductor chip (wafer, die). The higher the junction temperature, the earlier the light decay occurs. If the junction temperature is 105 degrees, the lifetime of brightness reduction to 70% is only 10,000 hours, there are 20,000 hours at 95 degrees, and the junction temperature is reduced to 75 degrees, the life expectancy is 50,000 hours, and the temperature can be extended to 65 degrees, 90,000 hours. Therefore, the key to extending the life is to reduce the junction temperature. The key to lowering the junction temperature is to have a good heat sink. So how do you systematically identify the heat dissipation of LED lamps?


Generally, the junction temperature of the LED rises and the luminous flux decreases. Then, as long as we measure the illuminance change of the luminaire in the same position, we can reverse the change of junction temperature. The specific method is:


1. Choose a place that is not subject to external light interference, preferably at night, turn off other lights;


2, turn on the light in cold state, immediately measure the illuminance of a position, record the reading at this time as "cold illuminance";


3. Keep the position of the luminaire and the illuminometer unchanged, and the luminaires continue to work;


4. After half an hour, read the illuminance value here and record the reading as “hot illuminance”;


5. If the two values are similar (10~15%), the heat dissipation system of the lamp is basically good;


6. If the two values are far apart (greater than 20%), the heat dissipation system of the lamp is questionable.


In addition, we can't just look at the cost to determine the quality of the radiator, we have to choose the most cost-effective


1, the hand touch the radiator is very hot, certainly not good, the hand touch the radiator is not hot is not necessarily good;


2, in the case of reasonable design, the same weight, surface area, heat dissipation is good;


3, the same material, the same surface area, the heavier the weight, the heat is good.


4. The fins of the fin heat sink are not as good as possible. The denser the better.


Light decay is an inevitable problem in the work of lamps. When purchasing lamps, you must choose lamps with better quality and heat dissipation, reducing the workload.