LED Mounting

[Jon86]

Sorry to bother you guys with another LED question,
But I'm looking at buying one of those cheap Star-Mounted LEDs from Ebay, and I was wondering if they need to be mounted on anything else for heatsinking? Or will the star do the job?
The ones I'm looking at are 5W and 10W, could the stars dissipate that sort of power? 
I'm going to be building it onto a tin so I could attatch it to that if need be.

[croberts]

Hello Jon86

You can determine this for yourself. Attach a temperature probe to the LED substrate (I suppose in your case that would be the star) and light the LED with whatever driver you are using. Note the temperature rise over ambient (room temperature) in free air. LED manufacturers will specify a max LED operating temperature for the LED (70 to 85 degrees C). If you operate the LED over that temperature one of the usual consequences is the life of the LED will be shortened from the specified 50000 hours or so according to some derating specification. You will probably find you will have to attach the LED to a heat sink. Star LEDs will probably not have mounting holes so you will have to do the attachment with thermal epoxy.

[Jon86]

Thanks for the advice.
I haven't bought any yet, but they're quite cheap so that shouldn't be a problem.

[croberts]

Hello Jon86

One more point I would make. You said you would be mounting the LED to a tin. Tins are usually made of thin metal. Should you determine you need a heat sink (I think you will) remember the effectiveness of a heat sink is mainly determined by the surface area exposed to free air and the conductivity of the heat sink material. Conductivity here refers to heat conductivity but there is a parallel to electrical conductivity. In other words a thin heat sink will not be as effective given the same surface area as a thicker heat sink. You will probably find the thin tin is a poor heat sink.