LEDs are funny things - and so is the brain<->eye connection.
For high brilliance, the normal method of operation is very high current pulses to the LED but at the low duty cycle. Try one of the 10mA LEDs already mentioned, pulse it at 50mA but with a 10:1 duty cycle so the average current is 5mA and hence the power dissipation is well within spec. This will produce a very bright light and at a high frequency (10KHz say) there will be no visible flashing.
The next bit is where the eye<>brain connection comes in. Try sitting in a dark room for 5 minutes and then fire either a photoflash or just turn a bright light on and off very quickly (say half a second). While sitting there in the dark you'll be able to 'see' the whole room due to the after image that persists in the photo receptors of the retina. Same with pulsed LEDs - you only see the bright bits, not the average or the dark bits in between.
My recommendation - never use a passive ballast on an LED if you want brilliance and low power.
Robin - Down Under (or are you Up Over)
