how do you calculate overdrive for small LEDs? (8mm)

I know that people routinely overdrive high-amperage LED lights. I could probably figure out what levels and heatsinks are appropiate for those easily.

What about smaller lights? Specifically, I'm looking at a 3.3-3.4 volt, 20ma reccomended, 26ma maximum light. (8mm)

I'm running it at about 25ma right about now, and I'd REALLY like to increase its power levels.

what's the likely relationship between lifespan and overdrive? between overdrive and brightness? how big does the heatsink need to be?

I ran a quick search on the forums, but that all seemed focused on larger lights,

also posting this in custom and modified.

Hrmm... That's hard to even take a stab at. I mean, there are LEDs with a suggested use at 30ma. Some of them will die very quick deaths at 50ma and some will last many, many hours at 100ma.

Can you provide a link to where you got the LEDs? And are you going to use a constant current regulator such as a DownBoy or something? And are you wanting to run a single LED or several in a small array?

These answers won't help me much, but might help those more knowledgable to answer your question.

The small LEDs usually rely on power being removed via the connection wires, so there is not much margin. If you are already at 8mm, you probably can fit either a Cree of Lumileds 1 watt in there for only a few $s. It will be much brighter at the same 30ma (as in 4-5 x) and you can drive them up to 100ma without thinking about special heat sinking.

The small LEDs tend to already be driven fairly hard due to the very small die size needed for that price point.