Uncut SMJLED in a keychain light?

I've been contemplating ordering parts & sticking an SMJLED into a 2x CR 2016 keychain light.

I'm wondering brightness and runtimes to 50% with this setup compared to say... a 40k mcd LED in the same host.

Would direct driving an SMJLED with CR2016's even push it at optimal levels?

I'm on uncertain ground here, but it might be safer to replace a red 5 mm LED with a keychain using a single 2032 cell. Even with the internal resistance of the 2x2016 cells, the voltage at the new LED might be excessive.

I put the earlier MJLED into a penlight-- replacing a fairly dim orange LED-- and far it's great. That's using two AAAA alkalines. (Streamlight Stylus (2xAAAA)

I've used several SMJLED's in various mods, but I think you have a good chance of burning out the SMJLED if put in a 2 button cell keychain light. The reason is that the SMJLED's are the efficiency king and designed to put out max light at 3 volts, they don't like to be overdriven and burn out fairly quickly at currents over 100-150 ma. The typical 2 cell keychain lamp is 6 volts, but the led supplied with it tolerated overdriving much better, and usually has a Vf much nearer 4 volts than the SMJLED. Particularly risky if the button cells are new lithium cells.

If you try it, let us know how it turns out.

Holland

I'll probably use a single CR2032 host then.

What i'm really looking for is brightness vs runtime :\

Would the CR2032 last for long running the SMJLED?

To determine the runtime with a 2032, just divide the amp-hour rating of the 2032 cell by the amp-hour rating of a pair of AA cells and multiply by the number of hours of useful light from the AAs. For occasional use, the 2032 cell might not be too bad.

I converted an old M*glite with an SMJLED and did an informal test: I removed the head, putting it in candle mode and placed the LED between my lips. I found it surprisingly warm (not hot), so it's likely drawing a fairly healthy current.