What is "Half-hour illuminance method"?
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Author : Crownda.LED
Update time : 2021-08-14 15:35:27
What is "Half-hour illuminance method"?
As we said before, the general LED junction temperature increases, the luminous flux will decrease. Then, as long as we measure the illuminance change of the lighting LED lamp at the same position, we can inversely deduce the change in junction temperature.
"Half-hour illuminance method" indirect measurement of junction temperature changes.
First, choose a place free from external light interference and light up the LED fixtures.
After lighting up, take an illuminance meter and measure it immediately, for example, 1000 lx.
Keep the position of the lamp LED and the illuminance meter unchanged. After half an hour, take the illuminance meter and measure it again. It means that the luminous flux has dropped by 50%. It's already too hot inside, and it's pretty good when you touch the outside, indicating that the heat hasn't come out, and it's bad. If it is measured to be 900 lx, and the illuminance has only dropped by 10%, it means that it is a normal data and the heat dissipation is good.
The scope of application of the "half-hour illuminance method"
We list the "luminous flux VS junction temperature" curve of several commonly used chips. From this curve, it can be seen that how much lumens the luminous flux drops can indirectly know how many degrees Celsius the junction temperature has risen.
SMD3030 chip, the luminous flux is reduced by 20% compared with 25 ℃, the junction temperature has exceeded 120 ℃
SMD5050 chip, the luminous flux is reduced by 20% compared with 25℃, and the junction temperature has exceeded 120℃
SMD5630 chip, the luminous flux is reduced by 20% compared with 25 ℃, the junction temperature has exceeded 140 ℃
It can be seen from the above figures that if the illuminance in the hot state is reduced by 20% compared with the cold state after half an hour, the junction temperature has basically exceeded the tolerance range of the chip. Basically, it can be judged that the cooling system is unqualified.
Of course, this is most of the cases, and everything has special cases, as shown in the figure:
Of course, for most LEDs, we can judge whether it is good or not by using the half-hour illuminance method, within a 20% drop.
Have you learned it yet? You must pay attention when choosing LED lighting lamps in the future. You can't just look at the appearance of the lamps, but to choose the right lights LED.
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