Compared with other ordinary lighting fixtures, the most prominent advantage of LED panel lights is long life. It can be said that LED lighting has been praised by consumers as the representative of "longevity lights".
At present, LED panel lights have been widely used in the field of indoor lighting, and people's understanding of it has become more and more in-depth. So how to understand and understand the life of LED panel lights? .
1. Temperature coefficient of LED volt-ampere characteristics
We know that LED is a semiconductor diode, it has a volt-ampere characteristic like all diodes, and like all semiconductor diodes, this volt-ampere characteristic has a temperature characteristic. Its characteristic is that when the temperature rises, the volt-ampere characteristic shifts to the left.
2. LED light decay:
Most white LEDs are obtained by illuminating a blue LED with a 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 LEDs. Another is the light decay of phosphors, and the decay of phosphors at high temperatures is very serious. The light decay of various brands of LEDs is different. The light 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, the earlier the light decay occurs, that is, the shorter the life span. Therefore, the key to prolonging the life is to reduce the junction temperature.
3. How to measure junction temperature
Junction temperature seems to be a temperature measurement problem, but the junction temperature to be measured is inside the LED, and a thermometer or thermocouple cannot be put into the PN junction to measure its temperature. Of course, its case temperature can still be measured with a thermocouple, and then its junction temperature can be calculated based on the given thermal resistance Rjc (junction to case). But after installing the radiator, the problem becomes complicated again.
Because the LED is usually soldered to the aluminum substrate, and the aluminum substrate is mounted on the radiator, if only the temperature of the radiator shell can be measured, then a lot of thermal resistance values must be known to calculate the junction temperature. Including Rjc (junction to case), Rcm (case to aluminum substrate, in fact, it should also include the thermal resistance of the film printed plate), Rms (aluminum substrate to heat sink), Rsa (heat sink to air), as long as there is one Inaccurate data can affect the accuracy of the test.
4. How to specifically measure the junction temperature of LEDs.
Now take an LED panel light as an example to illustrate how to specifically measure the junction temperature of the LED. It is required that the LEDs have been installed in the heat sink, and a constant current driver is used as the power supply.
At the same time, pull out the two wires connected to the LED. Connect the voltmeter to the output (the positive and negative poles of the LED) before powering on, then turn on the power, and before the LED heats up, immediately read the voltmeter, which is equivalent to the value of V1, and wait At least 1 hour, when it has reached thermal equilibrium, measure it again, the voltage across the LED is equivalent to V2. Subtract these two values to get the difference. This is removed by 4mV to get the junction temperature. The junction temperature obtained by this method must be much more accurate than measuring the temperature of the heat sink with a thermocouple and then calculating the junction temperature.
5. How to predict the life of LED panel lights.
It seems that it should be very simple to infer the life from the junction temperature. Just check the curve in the figure and you can know that the life corresponding to the junction temperature of 95 degrees can be obtained. The life of the LED is 20,000 hours. However, this method still has certain credibility for indoor LED panel lights. If it is applied to outdoor LED lamps, especially high-power LED street lamps, there are still many uncertainties.
6. How to extend the life of LED panel lights
The key to extending its life is to lower its junction temperature. The key to lowering the junction temperature is to have a good heat sink. The heat generated by the LED can be dissipated in time. In fact, this is a junction temperature measurement problem. If we can measure the junction temperature that any radiator can achieve, then not only can we compare the heat dissipation effects of various radiators, but also know that after using this radiator Achievable LED life.
Compared with other ordinary lighting fixtures, the most prominent advantage of LED panel lights is long life. It can be said that LED lighting has been praised by consumers as the representative of "longevity lights".
At present, LED panel lights have been widely used in the field of indoor lighting, and people's understanding of it has become more and more in-depth. So how to understand and understand the life of LED panel lights? .
1. Temperature coefficient of LED volt-ampere characteristics
We know that LED is a semiconductor diode, it has a volt-ampere characteristic like all diodes, and like all semiconductor diodes, this volt-ampere characteristic has a temperature characteristic. Its characteristic is that when the temperature rises, the volt-ampere characteristic shifts to the left.
2. LED light decay:
Most white LEDs are obtained by illuminating a blue LED with a 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 LEDs. Another is the light decay of phosphors, and the decay of phosphors at high temperatures is very serious. The light decay of various brands of LEDs is different. The light 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, the earlier the light decay occurs, that is, the shorter the life span. Therefore, the key to prolonging the life is to reduce the junction temperature.
3. How to measure junction temperature
Junction temperature seems to be a temperature measurement problem, but the junction temperature to be measured is inside the LED, and a thermometer or thermocouple cannot be put into the PN junction to measure its temperature. Of course, its case temperature can still be measured with a thermocouple, and then its junction temperature can be calculated based on the given thermal resistance Rjc (junction to case). But after installing the radiator, the problem becomes complicated again.
Because the LED is usually soldered to the aluminum substrate, and the aluminum substrate is mounted on the radiator, if only the temperature of the radiator shell can be measured, then a lot of thermal resistance values must be known to calculate the junction temperature. Including Rjc (junction to case), Rcm (case to aluminum substrate, in fact, it should also include the thermal resistance of the film printed plate), Rms (aluminum substrate to heat sink), Rsa (heat sink to air), as long as there is one Inaccurate data can affect the accuracy of the test.
4. How to specifically measure the junction temperature of LEDs.
Now take an LED panel light as an example to illustrate how to specifically measure the junction temperature of the LED. It is required that the LEDs have been installed in the heat sink, and a constant current driver is used as the power supply.
At the same time, pull out the two wires connected to the LED. Connect the voltmeter to the output (the positive and negative poles of the LED) before powering on, then turn on the power, and before the LED heats up, immediately read the voltmeter, which is equivalent to the value of V1, and wait At least 1 hour, when it has reached thermal equilibrium, measure it again, the voltage across the LED is equivalent to V2. Subtract these two values to get the difference. This is removed by 4mV to get the junction temperature. The junction temperature obtained by this method must be much more accurate than measuring the temperature of the heat sink with a thermocouple and then calculating the junction temperature.
5. How to predict the life of LED panel lights.
It seems that it should be very simple to infer the life from the junction temperature. Just check the curve in the figure and you can know that the life corresponding to the junction temperature of 95 degrees can be obtained. The life of the LED is 20,000 hours. However, this method still has certain credibility for indoor LED panel lights. If it is applied to outdoor LED lamps, especially high-power LED street lamps, there are still many uncertainties.
6. How to extend the life of LED panel lights
The key to extending its life is to lower its junction temperature. The key to lowering the junction temperature is to have a good heat sink. The heat generated by the LED can be dissipated in time. In fact, this is a junction temperature measurement problem. If we can measure the junction temperature that any radiator can achieve, then not only can we compare the heat dissipation effects of various radiators, but also know that after using this radiator Achievable LED life.
