On 6/7/07, Russell McMahon wrote: > > That said, I was looking at the > specification for some CREE 1 to 5W LEDs recently - direct competitors > for Luxeons in many applications - and their optimum Lumens per Watt > is indeed at 350 mA with a significantly lower figure at 700 mA. Still not optimum at 350mA - that's simply the lower current which they bin the LEDs at. Efficiency is better yet for these LEDs at even lower drive currents. If we're going to play references, then see the top figure on page 5 of http://www.cree.com/products/pdf/XLamp7090XR-E.pdf :-) Or better yet, here's some real world testing http://www.candlepowerforums.com/vb/showthread.php?t=152094 where as you can see the luminous efficiency is increasing right down to the lowest current measurement at 20mA, and shows the effect is actually pretty significant (50% better efficiency at 350mA compared to 1A). I'm still not sure what evidence you've given to prove the assertion that I'm wrong, let alone very wrong in my comments about efficiency improving with lower drive levels - plenty of evidence for my position. Looking at those docs of yours, it's obvious there are cases where keeping the colour the same is important, such as in displays. Meanwhile I'm interested in the very specialist area of battery powered high intensity lighting where efficiency is everything - of course my needs may not be the same as Ariel's. I should point out though that whatever those docs of yours suggest I notice no issues at all with running strings of 3 or 4 Cree LEDs at currents between 60mA and 1A - if the brightness varies between the different LEDs in the string I can't say it's something I've noticed given I'm using the LEDs to illuminate rather than staring into them! Chris -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist