Fixed light 700mA heatsink question

[KentS]

Hi
I've started a project of making a small light with CREE LEDs for our guest bathroom. I will be using http://www.dealextreme.com/details.dx/sku.13741. I've used theese on a bike light and is very impressed with the heat sinking abilities. However, this will be a fixed light ofcourse, possibly on for hours on end and without much air movement around it. On the bright side it will not be enclosed. I think 350mA will be perfectly safe, but how about 700mA, will I shorten the LEDs lifespan? If I go for 700mA can I use the two 230V->350mA constant current LED driver that I have got in parallel or will I have to get a 700mA driver?

 

[LukeA]

350mA is a really decent amount of light. I would just use that. In fact I did.

 

[blasterman]

There's a comment in the review section that you can take with any amount of granulated salt you wish:

"With the LED driven at 700mA all of the casing is warm within minutes. The Star itself is still only lukewarm"

I would really have to try the product myself to commit to solid advice, but your experience along with the above comment tends to indicate that it's possible to use 700mA. Obviously at the least we'd expect the fixture to be in the open and not mounted inside drywall or something.

I've experimented with all kinds of ad-hoc heat-sinking, from pipe fittings to rubber banding stars to a carpenter's level. My general rule of thumb is the heat sink can get luke warm to the touch, but getting warmer than that doesn't contribute to the longevity of the emitter. This is highly subjective of course. I just kind of know where that point is and don't go beyond it.

As per above, I've never seen much reason to go beyond 700mA (unless it's a K2, which I avoid anyways). Why not just get one, and let it run for an hour to see how hot it gets at different current levels?

 

[purduephotog]

350mA is a really decent amount of light. I would just use that. In fact I did.

I run a 3 watt LED (the 3 - color star) in this casing. So far it's handled just fine- it's used in a microscope as I needed the extra colors.

I've never left it on that long- I used Arctic Silver heat sinking compound to transfer- works just fine on battery power, but I typically don't leave it on for more than 15 minutes.

I could test it at some point... when I can get to that side of the room that has my microscope again

 

[R33E8]

You could try a heat sink from cooler master specifically made for LEDs... Such as this one: ECB-00394-01-GP

Rated for 5.3 watts according to Cooler Master's website..

http://ecd.coolermaster.com/english/products/products.php?_ledlist

I think you can get them from mouser..

 

[SafetyBob]

Yes you can get those from Mouser, but I would just give it a good try with what you have your hands on.

I agree that more than likely 350mA should be fine, and provide all the light you need, but if you do turn it up, just do a good test run over the weekend. I would think within an hour you will know if 700 is to much.

Bob E.