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I am building a SAD (Seasonal Affective Disorder) light box - its a super bright light.

The specs of the LEDs I am using:

50W Warm White LED IC High Power Outdoor Flood Light Lamp Bulb Beads Chip DIY
 Lighting color: warm white
 Color temperature: 3000K 
 Beam angle: 120 degree
 Working voltage: DC 32-34V
 Working current: 1500mA
 Power: 50W
 Luminous flux: 3800LM 
 Size: 52 x 46mm

Although these specs don't specify the maximum temperature they can handle prior to failure, what temperatures can LEDs typically withstand?

As a ball park figure I can tell you an Intel CPU is recommended to stay below 70°C but can handle upto 100°C at most - but I don't know what the thresholds for LEDs are!

I'm using a coolermaster i30 on a 150x150mm copper plate to cool 9 of these LEDs, the i30 is supposed to be able to "cool to 320Watts", which I would assume means it can keep a 320 Watt CPU below 70°C

Lightbox Core

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Be careful about shielding them from direct vision, you're starting to get to the intensities where LEDs will burn your retinas. They put out semi-coherent light which can be damaging if shined directly into your eyes. You're lucky if the burned trail after-image lasts a day or two. –  Fiasco Labs Jan 24 at 2:28
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1 Answer

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It depends how long you want them to last. The hotter they are, the faster they die; the cooler they are, the longer they last.

Parts from reputable suppliers will have temperature specifications tied to lifetimes, and they will also have thermal resistance specified - cooling the plate to 70C does not mean the active area of the LED would be at 70C... - based purely on the specs (and lack of specs) I'm guessing these are more casually sourced (direct from China via ebay, perhaps?) and may already be quality control rejects to take that path.

You should shoot for a lower temperature at the plate. And turn it over if you want the heat pipes to work.

Some better specified ones I have to play with spec an absolute maximum junction temperature of 125C, but that's at a point where they are severely derated and about to expire. Maximum current allowed starts to drop at 65C ambient, which is a good indication that they should be operating below that temperature in a well-designed fixture. A somewhat higher end one I also have to play with increases the max junction to 150C. But every step from the junction to ambient has thermal resistance, and that raises the junction temperature relative to ambient temperature. Aside from shorter life, high temperatures also reduce LED light output.

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Why would turning it over make the heat pipes work? –  ClothSword Jan 24 at 15:47
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Heat pipes are affected by gravity. While wicking can overcome some of this, heat pipes work best when the heated part is down and the cooled part is up, since they operate by boiling a liquid and condensing it, then returning the condensed liquid to the heated area to boil again. This works much better when working with, not fighting, gravity. –  Ecnerwal Jan 24 at 16:18
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