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How to measure and calculate the life of LED panel lamp?
LED panel lights have many advantages, the most important of which is that they have been used for a very long time, and the available range of LED panel lights is also very wide.
compared with other common lighting lamps, LED panel lamps have the most prominent advantage of long service life. It can be said that, at present, LED lighting has been called the representative of 'longevity lamp' by consumers.
at present, LED panel lights have been widely used in the field of indoor lighting, and people know more and more about them. So how to understand and calculate the life of LED panel lamps?
1. The temperature coefficient of LED volt-ampere characteristic
we know that LED is a semiconductor diode, which has the same volt-ampere characteristic as all diodes, also like all semiconductor diodes, this volt-ampere characteristic has a temperature characteristic. Its characteristic is equal to when the temperature rises, the volt-ampere characteristic shifts to the left.
2. Light attenuation of LED:
most white LEDs are obtained by Blue LED reflecting yellow phosphor. There are two main reasons for LED light decay. One is the light decay of blue LED itself. The light decay of blue LED is much faster than that of red, yellow and green LED. Another is the light attenuation of the phosphor, which is very serious at high temperatures. The light attenuation of various brands of LED is different. The light attenuation of LED is related to its junction temperature. The so-called junction temperature is equal to the temperature of semiconductor PN junction. The higher the junction temperature, the earlier the light attenuation appears, which is also equal to the shorter the service life. Therefore, the key to extending life is to lower the junction temperature.
3. How to calculate junction temperature
junction temperature seems to be a temperature measurement question, but the junction temperature to be measured is inside the LED, never put a thermometer or thermocouple into a pn junction to measure its temperature. Of course, its shell temperature can still be measured by thermocouple, and then according to the given thermal resistance Rjc (Knot to the shell), Can calculate its junction temperature. However, after installing the radiator, the question becomes complicated again.
Since the general LED is soldered to the aluminum substrate and the aluminum substrate is installed on the radiator, if only the temperature of the radiator housing can be measured, then to calculate the junction temperature, one must know a lot of thermal resistance values. Contains Rjc (Knot to the shell), Rcm ( The outer casing to the aluminum substrate should also contain the thermal resistance of the film printing plate), Rms (Aluminum substrate to radiator), Rsa (Radiator to air) In the meantime, only one data inaccuracy will affect the accuracy of the test.
4. How to calculate the junction temperature of LED.
now take an LED panel lamp as an example to explain how to measure the junction temperature of LED. The LED is now installed in the radiator and the constant current driver is selected as the power supply.
Together, the two wires connected to the LED should be LED out. Connect the voltmeter to the output when energized (Positive and negative LEDs) , Then turn on the power supply, read out the voltmeter reading immediately before the LED heats up, which is also equivalent to the value of V1, and then wait for at least 1 hour until it has reached thermal balance, once again, the voltage at both ends of the LED is commensurate with V2. Subtract the two values to get the difference. After being removed by 4mV, the junction temperature can be obtained. The junction temperature obtained by this method is definitely much more accurate than calculating the junction temperature by measuring the temperature of the radiator with a thermocouple.
5. How to predict the life of LED ultra-thin panel lamp.
judging life from junction temperature is as if it should be very simple. Just check the curve of the figure, we can know the life span corresponding to the junction temperature of 95 degrees, and we can get the life span of LED to be 20 thousand hours. However, this method is still necessary for indoor LED panel lamps. If it is applied to outdoor LED lamps, especially high-power LED street lamps, there are still many uncertain factors.
6. How to extend the life of LED panel lamp
The key to extend its life is to reduce its junction temperature. The key to lowering the junction temperature is to have a good radiator. The heat generated by the LED can be emitted in time. In fact, this is a question of measuring junction temperature. If we can measure the junction temperature that any radiator can reach, then we can not only compare the heat dissipation effect of various radiators, but also can know the LED life that can be completed after selecting this kind of radiator.
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