# largest size of led without a need of a heat sink



## yousaf465 (May 2, 2011)

What is the size of LED which can be used without any heat sink.


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## saabluster (May 2, 2011)

yousaf465 said:


> What is the size of LED which can be used without any heat sink.


 All LEDs can be used without heatsinks. It just depends on the drive level. Keep it low enough and any LED will be fine.


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## yousaf465 (May 2, 2011)

low drive level I don't understand ? please explain in more basic terms.


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## CKOD (May 2, 2011)

That being said, the largest LED that was meant to be run full power without a heatsink is the "superflux" style LEDS in the 4-pin package, usually the forward current on those was ~100mA Doesnt mean that you dont have to worry about heat though. Made a taillight for my buddys bike with quit a few of them, packed as tight as they could fit, cast in epoxy, and with the stop and turn lights on for testing, it got surprisingly warm. Well maybe not so surprising at 12W total power.

Though going with what saabluster said, a bunch of modern power LEDS on minimal stars, run at low currents without extra heatsinking, and be quite efficient too ) Not so easy on the wallet though.


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## Th232 (May 2, 2011)

If you put no power into an LED, obviously no light or heat will be generated. In order to get light, you need to put power in. More power (read: higher drive level) = more light. However, more power means the LED will get hotter. Enough heat and the LED will be destroyed. If you keep the power low enough the heat will be removed by natural means and you don't need a heatsink.

I've got a question about your question, what do you mean by "largest"? Did you mean physically largest, or brightest? Bear in mind that the two properties may not correlate, some of the larger LEDs these days put out less light than the smaller ones.


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## onetrickpony (May 2, 2011)

Th232 said:


> If you keep the power low enough the heat will be removed by natural means and you don't need a heatsink.


 
So you're saying heatsinking is unnatural? :devil:


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## bshanahan14rulz (May 2, 2011)

he's saying heatsinking is supernatural ;-)


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## blasterman (May 2, 2011)

XP-G can be run at least to 175mA on a basic star without needing additional heatsinking. Barely gets warm. 350mA is manageable, but will cut into the longevity curve.


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## onetrickpony (May 2, 2011)

bshanahan14rulz said:


> he's saying heatsinking is supernatural ;-)


 
Oh, I get it, every time an led is properly heat-sinked, an angel gets its wings?


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## Th232 (May 2, 2011)

Lol, you guys got me there, bad choice of words.


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## cloverhsu7 (May 3, 2011)

Th232 said:


> If you put no power into an LED, obviously no light or heat will be generated. In order to get light, you need to put power in. More power (read: higher drive level) = more light. However, more power means the LED will get hotter. Enough heat and the LED will be destroyed. If you keep the power low enough the heat will be removed by natural means and you don't need a heatsink.
> 
> I've got a question about your question, what do you mean by "largest"? Did you mean physically largest, or brightest? Bear in mind that the two properties may not correlate, some of the larger LEDs these days put out less light than the smaller ones.



simple and clear explaination


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## yousaf465 (May 3, 2011)

I meant the brightest. Superflux Led it doesn't come in white.

XP-G  I think this might be useful.


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## Th232 (May 3, 2011)

If you're looking for the most light without heatsinking then I'd definitely recommend the XP-G on a star. Just make sure to stay under the drive levels that Blasterman posted, and if you're not even using a star then you'll have to decrease the current even further.


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## RedForest UK (May 3, 2011)

Why is there a need for no heatsinking? You will need to make a compromise between the most efficient and the most robust led available. 

The brightness of an led depends on how much current you feed it, but the more current you feed an led the more heat is given off as well, some led's can handle excess heat better than others however. For example cree XR-E's can handle it better than XP-E's which use the same led die, however this is only really due to what could be referred to as better heatsinking/thermal mass of the led package itself.

If space is the issue you might be better using at least some minimal heatsinking to allow certain leds to be driven to higher currents for more light.


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## onetrickpony (May 3, 2011)

I was kind of thinking the same thing, 500 ma or more is easily safe if you mount a star to a little chunk of aluminum. Why no heatsinking at all anyway?

If you really can't heatsink, I'd go with multiple leds at very low currents, lumen output is additive. You could run 3 XPG's at 500 ma and it should actually be brighter than one at 1.5a due to the higher efficiency you get at lower currents.

EDIT: Why not use XM-L's, they're even more efficient.


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## saabluster (May 4, 2011)

yousaf465 you really need to specify what your end goal is and why you can't use a heatsink for us to direct you properly. For instance you may be referring to intensity when you say "brightest" or you may in fact mean the most lumens. I get the feeling you are in way over your head in whatever you are trying to accomplish.


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## onetrickpony (May 4, 2011)

saabluster said:


> yousaf465 you really need to specify what your end goal is and why you can't use a heatsink for us to direct you properly. For instance you may be referring to intensity when you say "brightest" or you may in fact mean the most lumens. I get the feeling you are in way over your head in whatever you are trying to accomplish.


 
About time somebody said it.

We do want to help you, but without know the whys and the hows, there's just no way we can.


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## onetrickpony (May 4, 2011)

saabluster said:


> yousaf465 you really need to specify what your end goal is and why you can't use a heatsink for us to direct you properly. For instance you may be referring to intensity when you say "brightest" or you may in fact mean the most lumens. I get the feeling you are in way over your head in whatever you are trying to accomplish.


 
About time somebody said it.

We do want to help you, but without knowing the whys and the hows, there's just no way we can.


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## Jackasper (May 21, 2011)

*POOF !*


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