Originally Posted by
01 CAt Man Do
Not sure about a 400+ lumen output with just one XP-E2. Normal driving current for these is listed around 700ma. Yes you can over drive the emitter but that is only going to give you so much. Don't believe output curves are going to be infinitely linear. At some point the curve will taper off as the emitter reaches it's heat limit. You might be able to run at 1.5A and that might get you something like 230-240 lumen...hard to say for sure. Surly you can also expect the output to drop significantly once the emitter begins to over heat ( which it will do when over driven )
The current highest binning for XP-E2 is Q3, which is 93.9 lum/350mA. The driver I'm using is 1.7amp, which straight math says is 450 lumens at the emitter. If you look at the data sheets -
http://www.cree.com/LED-Components-a...nal/XLamp-XPE2
You can see that lumens x amps is very linear. The reduction in output comes when junction temp (Tj) rises. The forced convection of using a light on a bike is significant - when I use my XML2 driven at 3.5 amps in a solar force host, the light does not even get warm to the touch. According to the data sheets, at Tj=25c, output =100%, and at Tj=50c, output =87%. As I mentioned, I expect the light to be completely cool to the touch while riding, so Tj<50c doesn't seem unreasonable, so therefore 390 emitter lumens doesn't seem unreasonable to expect. Yes, OTF lumens will be less - but then again, I've never seen bike light manufacturers advertise OTF lumen, much less ANSI lumens, so I feel my 390lm estimate is fairly apples-to-apples.