This is an amazingly bright LED combined with an AP2502 linear Constant Current Sink driver chip.
I'm running it at 3V input and it is sinking 20 mA while "on", at a frequency of 3 kHz and duty cycle of 10 percent ON. So it's drawing an average power of 6 milliWatts.
If I run it fully 100 percent ON, it draws 60 mW and is so bright it's probably dangerous to look directly at it. It also runs cool, without a heatsink.
The AP2502 constant-current sink eliminates the need for series resistors and is very efficient itself. Both the LED and the chip are surface-mount devices, very small.
I'll be doing further tests and demos of this setup. When used as the load to a Joule Thief I think it will produce more light for less average power than any other combination I've tested.
The parts were generously donated by a friend to TKLabs. Thanks, you know who!