Who can help to explain a temperature phenomenon of vehicle frog LED?

There is a big heatsink under LED board, most of heat will tranfer to heasink and dissipate to ambient.
(sorry the IR picture can not work, I will try.)

Hi DM51, Thanks for your opinion, my english is not good.

LED on board(a heatsink is under board) and IR pictures link:
http://13051785.photo.hexun.com/1677626_section.html

Errr... welcome to CPF, ltpeng31.

I'm not sure I understand what you're saying here (actually, I don't understand it at all). Are you using a translation program to convert your post to English? They sometimes produce strange results.

Your photos haven't worked either, so it is difficult to advise you.

ltpeng31 said:

A NICHIA LED, lighting at 4.5V 0.64A, temperature is 84.7C in IR camera, 84.6C thermal coupled (I set TC on LED substrate near LED bulb).
I used LOTUS Whiteboard pen sweared on LED package to avoid glare and make IR camera more efficiency. But an amazing thing followed, after power on, burst of white smoke, looks there is reaction happened, fortunately LED is still working.
Then, I took the camera, LED temperature is over 130C, thermal couple is 112C. but input power is still same 4.5V 0.6A.

What's the problem? Who can tell the cause?​

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Hmm, let me see if I can translate it...

I have a Nichia LED with specs of 4.5v and 0.64A on an infra-red (IR) camera on it, it normally reads 84.7C, whereas when I set the thermal couple near the LED, it reads 84.6C.

Now, I used some sort of marker to diffuse/reduce the glare on the LED to make the IR camera more efficient. However, by doing so, when I turned the power on, a puff of white smoke appeared out of no where. Despite the magic white smoke, the LED is still working.

After the above incident, I measured the LED's temperature and it now reads 130C, and the thermal couple at 112C even though the specs remain the same (ie. 4.5v and 0.64A).

Does any one have any idea what's caused the increase in temperature?

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Well, that's how I read his post.

I'm not real clear on where exactly you put the ink, but black ink in the vacinity of a powerful light source is going to heat up. An object that is white, or reflective, is not absorbing the light. Instead it is being reflected away and thus not heating up as much. If you add black ink, the color black appears that way because it is absorbing all light frequencies. And when it absorbs the light, it heats up. If the areas around the LED were colored black, it would absorb more of the light emitted from the LED and heat up more causing the temperature increase even though no more power was being used. If it was the clear LED dome itself that you applied the ink to, it would be even worse. The ink would tend to trap all the light, and all the heat, within the LED and cause even larger temperature changes.

Hmmm .... still no mention of * vehicle frog's * in the translation of the title.

Can you clear that one up for me ?
.

What is the suggested voltage and drive current to the LED?

4.5v sounds high for any LED normal. But if the dies are in series, then it makes more sense.

:welcome:

I remember reading somewhere that something painted black gives of more heat that something white. Perhaps that is the case with the op's LED?

dandism said:

I remember reading somewhere that something painted black gives of more heat that something white. Perhaps that is the case with the op's LED?

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Yes. I think he was attempting to use the black marker as an emissive coating. Interesting that he has access to equipment like that($Ks) but little understanding of how it all works. :thinking: