Luxeon Heat? Really?

I've had a couple of white Luxeon 1 stars running at 300ma for the past few days and really, these things don't put out the heat that I thought they would. I have just a small 1" square aluminum heatsink behind each with a some grease.

They're not even warm to the touch.

From what I gathered with the posts here, I had anticipated more of heat generated.

Could anyone confirm?

300ma is pretty low. I flicked a light of mine on the otherday while walking to keep my hands warm. Draws something like 1.4A from the battery...Most of that is going to the LED. Oh yeah, there's heat There is more at drive level and beyond. At lower current levels, they're more efficient.

philamint said:

They're not even warm to the touch.

From what I gathered with the posts here, I had anticipated more of heat generated.

Could anyone confirm?

Click to expand...

1. Heat output will vary depending on what current the LED is driven at.

2. Open air on an aluminum heatsink with thermal grease is a much better cooling method than stuffing it inside the head of a light. Therefore, in your testing, the temperature of the emitter will be much lower than when installed in a flashlight. The same emitter might get much hotter inside of a light, which gives people a false sense that it's somehow producing more heat. This leads me into the next point...

3. Heat transfer is not equal to temperature. A difference in temperature causes heat transfer. Thus, the "hand tests" that people perform by touching the body of their light and saying "ouch!" or "hey that's cool" mean squat. You need to look at the temperature distribution between the heat source and the heat sink, and know the thermal resistances, to calculate heat production of the emitter.

300 ma is low? Maybe I misread but I thought the Luxeon maximum was 325ma or so?

philamint said:

300 ma is low? Maybe I misread but I thought the Luxeon maximum was 325ma or so?

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There are different Luxeon series, based around different die designs, and within each series, there are multiple bins used to account for the variations due to manufacturing.

You can always overdrive or underdrive a LED, but overdriving will reduce the lifespan.

I think the Lux I is rated for 350ma.

low current, and that heatsink is huge (relatively speaking)

This might be better ask in a different forum but it is in keeping with the subject header.
If I wanted to use an LED flashlight for a hand warmer, how much energy is lost to light? As a hand warmer, would it be inefficient? :thinking:

Lite_me said:

This might be better ask in a different forum but it is in keeping with the subject header.
If I wanted to use an LED flashlight for a hand warmer, how much energy is lost to light? As a hand warmer, would it be inefficient? :thinking:

Click to expand...

Who needs light? Just put a resistance coil in the end of it with a variable current switch

My ROUGH interpretation of specs was that at 1W in open air, you didn't need much more than the "STAR" as heatsink. The 3W and 5W need more, and you have to pay
some attention if you're going to seal up the star (or an emitter) inside a flashlight body.
(and cooler is better. Who makes an LED flashlight with a fan?

My Raw Ns w K2 runs around an amp on hi and it does get warm but it is only used in bursts.