luxeons and temperature? advice please

I recently purchased my first luxeon leds (TX1J binning) and before firing one up in a simple circuit in serial with a resistor I thought I'd ask around for some advice regarding heat sinking. I don't want my new toys to go up in smoke right away /ubbthreads/images/graemlins/smile.gif

Many people are shouting "heat sink, heat sink!" here on CPF but it's a bit hard to picture the heat build-up when I've never actually seen/felt a Luxeon in action.

Does anyone have any approximate figures on how long it would take to damage a Luxeon III (3W) emitter without heat sinking at say 200 mA, 700mA and 1A? Seconds?
How about the same emitter but as a star, at those currents?

I am not really asking for exact lab results here. Just an approximation so I know how to set up a basic circuit and have time to measure any temperature increase without the led going pooooof in a few seconds /ubbthreads/images/graemlins/smile.gif

Would some thermal paste and an old processor heat sink be enough to keep the temp down?

Emitter:
200mA - probably would last a while, but it would definitely be running over maximum temperature

700mA - minutes to hours?

1A - minutes


Star:
200mA - you can run the star indefinitely at this current level

700mA - probably would last a while, but would be running over temp spec

1A - as above, but shorter lifetime

korpx,

The old processor heat sink would be fine. Lumileds suggests using non-conductive epoxy or you can also try some of the thermal conductive tapes.

An excellent introduction to thermal management for Lux IIIs can be found in Lumileds Application Brief 05 (AB05), found here:
http://www.lumileds.com/pdfs/protected/AB05.PDF

Hmm, maybe I should just start enclosing a copy of this with every Lux III, or at least the link.

An emitter at 100ma is supposed to be OK without a heatsink if used in open air. 200ma sounds right for a Star used in open air.

A heatsink from a CPU is designed to have air flowing over it, so it will probably work well if mounted outside an inclosure. Inside an enclosure it will be fairly inefective unless you have a fan moving air into and out of the enclosure.

A Star that is in good contact with the metal body of a flashlight effectively transfers the heat from the LED to the flashlight body where the heat will dissipate into the air and your hand. A star within a plastic flashlight will overheat without airflow.

Daniel

Starting around page nine is another very good read:

http://www.lumileds.com/pdfs/RD25.PDF

Thanks guys. That'll keep me busy reading for awhile.

Mounting it on a cpu heatsink with a fan will most likely do for my test setup just so I can satisfy my current curiosity over these luxeons' light output. /ubbthreads/images/graemlins/cool.gif