3v DD luxeon: heatsink needed?

I'm thinking of modding my Tekna Splash-lite to use an R2H Luxeon. The Splash-lite is a 1x123 plastic light with a #222 screw-base incan bulb. My idea is to just break out the globe and filament from the bulb and solder in the LED. At 3 volt direct drive it should be usefully bright while still underdriven for long runtime and low heat. Question is whether more heat sinking is needed. There's no metal flashlight body to conduct the heat to, just the bulb base. Any thoughts?

you always need to heatsink the led! /ubbthreads/images/graemlins/twakfl.gif

well, not always needed i guess, but still a good idea. generally, if using the star, and the current is under 100ma, then additional heatsinking isn't needed.

an r2h luxeon on a 123 will definately need heatsinking.

Roth, I'm not so sure. The Vf of an LED is a funny thing. The published Vf generally refers to the voltage dropped when the rated current flow is going through the emitter; but at lower voltage there's still some current flow, just not as much. Of course, at some point the voltage is simply too low for anything to happen at all.

Think of it like a dam across a river. Until the water reaches a certain height, nothing happens. At some point a teeny bit of water flows over the dam. From this point on, as the water rises higher and higher, flow over the dam increases more and more. That's kind of how it is with Vf and current flow.

With regard to the immediate question, the 3V from the 123 cell won't be enough for the full amount of current flow to occur, even in direct drive. My guess is that the star is enough heatsinking for such a case.

However, be careful paulr! This is a special case in which you effectively sidestep the normal situation. Roth's right with his advice on this for most cases... so go for it in this application, but always be careful!

Note that I'd never leave a bare emitter sitting there without some form of additional heatsinking, just that the star does give enough heatsinking for some limited applications such as yours.

with an r2h bin (or any 1w bin!), you're going to get a lot more than 100ma.
remember also, the 100ma is for the star, not the [/b]emitter[/b]

just go by my rule: "always heatsink as much as possible. overkill is your friend" /ubbthreads/images/graemlins/grin.gif

There's really no way to use the Star in the pr222 shell. I'd have to come up with a more complicated mod. Maybe I can add a resistor to keep the current under 100 mA. Another idea would be go up a voltage bin or two, i.e. trade the R2H for an R2J or K.

I agree with Rothrandir... If you're just using the emitter you should use a heatsink.