# 100w LED chip temp



## sportcoupe (Dec 5, 2016)

I have several cheap 100w LED's to play with. The spec sheet says max operating temp is 120 deg C (about 248 deg F). The LED's are designed to go on a heatsink. 

Would a standard computer CPU heatsink without a fan prevent the LED from exceeding it's max temp? I have no way to measure the temp on the back of the LED once attached to heatsink.

I'm trying to avoid the fan if it isn't required.


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## sportcoupe (Dec 6, 2016)

OK, has anyone used a 100w LED chip on a heatsink without a fan? How big (or small) of a heatsink did you use?


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## Lithopsian (Dec 6, 2016)

I would suggest you have no chance. Maybe with a heatsink the size of a laptop you could get away with it for a while, but not just a CPU heatsink. I think you'll struggle even with a fan, but I guess it depends how long you want the LED to survive. You can take a temperature from the front of the phosphor to give you an idea how things are going. Make sure everything is well-greased up!


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## Enderman (Dec 6, 2016)

Yeah a CPU heatsink with fan would work.
If you don't want a fan you need to use a much larger heatsink, something the size of an NH-D14 or around there.


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## sportcoupe (Dec 7, 2016)

I am currently using a standard $6 cpu heatsink with fan. It works easily. So easy I feel like the fan may not be required.


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## degarb (Dec 7, 2016)

I bought a 50 watt cool eBay ip65 Chinese, epistar 9x11inch sealed. . They claim over 90 lpw, I estimate , 58lpw to 65lpw (optimistically) , comparative lux v light distribution. Used it as a wakeup light this spring, accidentally left on when I went to work, the led burned out. . Worked fine for a few hours at a crack for many months, but apparently, not for many hours at a time. . I had a spare warm ebay 100 watt led chip laying around, so replaced the 50w with the 100w warm. . It is true the cools wake one up better. But still works better than a 800 lumen omni directional light bulb. . Who knows if under-driving will make the chip hardier than the 50w it replaced? . But I figure, sooner or later, I will forget to unplug, and will find out.


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## Lithopsian (Dec 7, 2016)

sportcoupe said:


> I am currently using a standard $6 cpu heatsink with fan. It works easily. So easy I feel like the fan may not be required.


 Only one way to tell  Note that with a chunky heatsink it might take quite a while to get really hot even if it is a true 100W LED. If it is like many of the cheap ones and really only 50W or less, it would take even longer. Do you have a temperature probe you can touch to the front of the LED? Or even an IR gun?


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## Enderman (Dec 7, 2016)

sportcoupe said:


> I am currently using a standard $6 cpu heatsink with fan. It works easily. So easy I feel like the fan may not be required.


You might not be driving it at 100W then...
Have you checked the voltage and current?
I have an XHP70 running at almost 90W and it gets hot fast even with a large 200W capacity CPU heatsink (no fan)


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## sportcoupe (Dec 7, 2016)

Lithopsian said:


> Only one way to tell  Note that with a chunky heatsink it might take quite a while to get really hot even if it is a true 100W LED. If it is like many of the cheap ones and really only 50W or less, it would take even longer. Do you have a temperature probe you can touch to the front of the LED? Or even an IR gun?



I have an ir temp gun but have not used it. The front of the led puts out a lot of heat from the light, that will mess up the reading I'm sure.


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## sportcoupe (Dec 7, 2016)

Enderman said:


> You might not be driving it at 100W then...
> Have you checked the voltage and current?
> I have an XHP70 running at almost 90W and it gets hot fast even with a large 200W capacity CPU heatsink (no fan)



My driver board is set at 36v and 3A CC. I am driving LED fully. My 25.2v lipo pack shows a 4.5A total draw while running.


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## Lithopsian (Dec 9, 2016)

Something doesn't add up. Like enderman, I've run at less than 100W on a big old Pentium 4 heatsink with a fan and it gets too hot to touch (50 - 60C). Only takes a few minutes.


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## sportcoupe (Dec 9, 2016)

I did a run time test and checked heatsink temp with IR gun today. Temp on face of $6 cpu heatsink (with fan) next to LED was only 195°F (90°C) after 1 hour. LED spec is 248°F max (120°C). Lipo 6s pack died at 1 hour also.


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## Enderman (Dec 9, 2016)

You want to keep LEDs as close to 20C as possible.
The hotter it gets the less output it has.


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## sportcoupe (Dec 9, 2016)

I really don't see a way to determine a slight reduction in light output of a 100w LED at 20°C vs. 90°C. The LED is very bright at startup and stays very bright as it warms up. Bright is bright. I can't see a difference.


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## Enderman (Dec 9, 2016)

Well yeah obviously you can't see a difference until the LED is half dead, but there still is a difference.
That's why people use integration spheres and luxmeters.
I would not be comfortable having one of my LEDs anywhere near 90C, that also severely degrades the lifespan.


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## ssanasisredna (Dec 9, 2016)

Enderman said:


> Well yeah obviously you can't see a difference until the LED is half dead, but there still is a difference.
> That's why people use integration spheres and luxmeters.
> I would not be comfortable having one of my LEDs anywhere near 90C, that also severely degrades the lifespan.



Most LEDs are quite happy to run at 90C for long long periods of time.

Good quality LEDs drop about 10% at 90C. That's pretty tolerable versus the alternative of an enormous heatsink in most cases. 10% drop in light output is not detectable by the eye.


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## Lithopsian (Dec 9, 2016)

Your definition of "hot" may be different to mine  I think 90C is hot. At a junction temperature of 90C (and you've probably exceeded that) an LED will typically degrade around five times as fast as at 60C. Maybe you can live with that and throw them away after a few thousand hours, and lifetimes at 90C are still generally tens of thousands of hours (to 70% output). Beyond 90C things get ugly very fast and somewhere not too far above 100C the LED will fail catastrophically. Your mileage may vary, LEDs have different specs, but cheap ones aren't renowned for performing well under stress. What people are happy with generally isn't the point, especially since very few people have run these things for even 10,000 hours yet - and the early adopters that have had them that long have probably got bored and replaced them with something even newer


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## ssanasisredna (Dec 9, 2016)

Lithopsian said:


> Your definition of "hot" may be different to mine  I think 90C is hot. At a junction temperature of 90C (and you've probably exceeded that) an LED will typically degrade around five times as fast as at 60C. Maybe you can live with that and throw them away after a few thousand hours, and lifetimes at 90C are still generally tens of thousands of hours (to 70% output). Beyond 90C things get ugly very fast and somewhere not too far above 100C the LED will fail catastrophically. Your mileage may vary, LEDs have different specs, but cheap ones aren't renowned for performing well under stress. What people are happy with generally isn't the point, especially since very few people have run these things for even 10,000 hours yet - and the early adopters that have had them that long have probably got bored and replaced them with something even newer




Many quality LEDs are good for 105C solder point temp at rated drive current and still pushing 50K hours to 70%. Some are rated to 135C junction temp with long operating life and even higher before catastrophic damage.

Degradation is usually a factor of drive current and operating temp, so a generalization of 5x life at 60C versus 90C would only be accurate in specific instances. In some instances, the difference between 55C and 105C (typical test temps for LM80), may be only a 2x improvement in life or less.

When portability is important, hours of operation rarely come into realistic play but weight does. I would generally run hotter and lose a bit of lumens to have something that can be light and easy to handle.


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## ssanasisredna (Dec 9, 2016)

sportcoupe said:


> I am currently using a standard $6 cpu heatsink with fan. It works easily. So easy I feel like the fan may not be required.



That fan could easily be providing a 5x increase in cooling over the heatsink on its own.


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## ssanasisredna (Dec 9, 2016)

sportcoupe said:


> I did a run time test and checked heatsink temp with IR gun today. Temp on face of $6 cpu heatsink (with fan) next to LED was only 195°F (90°C) after 1 hour. LED spec is 248°F max (120°C). Lipo 6s pack died at 1 hour also.



What color was the heatsink? If it was black (anodized), then that measurement could have been somewhat accurate though perhaps 10% lower than the real number. If it was bare aluminum, or even heavily oxidized aluminum then the actually temperature was a lot higher than your reading. If it was clear anodized then count on it being 20% higher. Those thermometers are usually calibrated for 0.95 emissivity ... but aluminum is almost always lower than that. You can cover it with a lot of black marker and get a better reading, even if black anodized. Even better would be black paint.


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## sportcoupe (Dec 9, 2016)

ssanasisredna said:


> What color was the heatsink? If it was black (anodized), then that measurement could have been somewhat accurate though perhaps 10% lower than the real number. If it was bare aluminum, or even heavily oxidized aluminum then the actually temperature was a lot higher than your reading. If it was clear anodized then count on it being 20% higher. Those thermometers are usually calibrated for 0.95 emissivity ... but aluminum is almost always lower than that. You can cover it with a lot of black marker and get a better reading, even if black anodized. Even better would be black paint.



Since I have a fan on the heatsink, the surface finish doesn't matter very much at all. Otherwise, the debate is still out on silver (bare) verses black heatsinks.


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## ssanasisredna (Dec 10, 2016)

sportcoupe said:


> Since I have a fan on the heatsink, the surface finish doesn't matter very much at all. Otherwise, the debate is still out on silver (bare) verses black heatsinks.



It matters when you are measuring the temp.

Jury not out on color. Black is better versus bare.


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## bwinzey (Dec 21, 2016)

Lithopsian said:


> Something doesn't add up. Like enderman, I've run at less than 100W on a big old Pentium 4 heatsink with a fan and it gets too hot to touch (50 - 60C). Only takes a few minutes.


I have a 100w LED running at 34v @ 3A(full draw) on an OEM FX-8120 heatsink. With the fan off, it will probably burn after a few minutes, but with the fan on, it's only warm to the touch and can run indefinitely (I left it on for 2 hours at full brightness and it was as warm as when I left it). I made sure to put plenty of thermal paste on it and it works fine, so I'm not sure what you're doing wrong. Is the LED you're running designed to be run at 100W? You gotta remember that LED's become EXTREMELY inefficient when driven above their specifications, and instead of creating more light, they will just create more heat.


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