LED panel lights have many advantages, the most important of which is that their use time is particularly long, and the range of LED panel lights is also very wide.
Compared with other general lighting fixtures, LED panel lights have the most prominent advantage equal to long life. It can be said that the current LED lighting is now called the representative of "long-life lights" by consumers.
At present, LED panel lights have been widely used in the field of indoor lighting, and everyone has become more and more aware of it. So how to understand and calculate the life of LED panel lights?
1. Temperature coefficient of LED volt-ampere characteristics
We know that an LED is a semiconductor diode. It has a volt-ampere characteristic like all diodes and the same as 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. The light decay of LED:
Most white LEDs are made from blue LEDs shining yellow phosphors. There are two main reasons for LED light decay. One is the light decay of blue LEDs. The luminous decay of blue LEDs is much faster than that of red, yellow, and green LEDs. Another is the light decay of the phosphor, which is very serious at high temperatures. The light decay of LEDs of various brands is different. The light decay of an LED is related to its junction temperature. The so-called junction temperature is equal to the temperature of the semiconductor PN junction. The higher the junction temperature, the earlier the light decay appears, which is also equal to the shorter the lifetime. Therefore, the key to extending life is equal to lowering the junction temperature.
3. How to calculate junction temperature
The junction temperature seems to be a temperature measurement question, but the junction temperature to be measured is inside the LED, so you can't use a thermometer or thermocouple into the PN junction to measure its temperature. Of course, its case temperature can still be measured with a thermocouple, and then based on the given thermal resistance Rjc (junction to case), its junction temperature can be calculated. But after installing the radiator, the question became more complicated.
Since the general LED is soldered to the aluminum substrate, and the aluminum substrate is mounted on the heat sink, if you can only measure the temperature of the heat sink case, you must know a lot of thermal resistance values to calculate the junction temperature. Contains Rjc (junction to the case), Rcm (the case to the aluminum substrate, the thermal resistance of the film printed plate should also be included in the meantime), Rms (the aluminum substrate to the heat sink), and Rsa (the heat sink to the air). An inaccurate data will affect the accuracy of the test.
4. How to measure the junction temperature of LED specifically.
Now take an LED panel light as an example to illustrate how to measure the junction temperature of the LED. The demand has now installed the LED in the heat sink, and the constant current driver is used as the power supply.
The two wires connected to the LED should be led out together. Connect the voltmeter to the output terminal (positive and negative of the LED) before powering on, and then turn on the power supply. Before the LED has heated up, immediately read the reading of the voltmeter, which is also equal to the value of V1, and then wait At least one hour, after it has reached thermal equilibrium, measure it again, the voltage at both ends of the LED is equal to V2. Subtract these two values to get the difference. After being removed by 4mV, the junction temperature can be obtained. The junction temperature obtained by using this method is definitely much more accurate than using a thermocouple to measure the temperature of the radiator and then calculating its junction temperature.
