On Fri, Feb 5, 2010 at 12:12 AM, Jake Anderson wrote: > Chris McSweeny wrote: >> On Thu, Feb 4, 2010 at 8:21 PM, M. Adam Davis wrote: >> >>> Further, Lumens specifically measures light output *as perceived by >>> the human eye*. =A0By pulsing the LED at higher than rated current, "the >>> human eye" may perceive significantly more light than running the LED >>> at its DC rating. >>> >> Actually no, it doesn't work like that. If you pulse an LED, the >> perceived brightness will be the brightness if it was on the whole >> time multiplied by the duty cycle. There is no magic to pulsing with >> LEDs. >> > http://www.ledsmagazine.com/news/5/5/11 Well there's the obvious big flaw as pointed out by Daniel - they suggest rather optimistically that LED device researchers should concentrate on improving efficiency for pulsed operations - which basically means reducing droop, something which isn't going away any time soon, if ever. So the perceived brightness for the same power input isn't actually better. How can a serious researcher can say "With this method, the brightness of LED with a luminance efficiency of 100lm/W can be simulated by using a 50lm/W LED," based on those results? Apart from that, a 5% duty cycle is itself quite a big flaw, as you only get any benefit running LEDs at very low power levels, which is totally the opposite of where this topic started with the excitement of just how many lumens you could get out of an LED. I have LED powered head torches and bike lights and even their dimmest battery saving setting is more than 5% of full power. I'm also pretty sceptical about how this very specific research will translate into the real world where you have multiple emitters and are viewing reflected rather than direct light. On Fri, Feb 5, 2010 at 12:22 AM, YES NOPE9 wrote: > I believe that an LED using 1A at 50% duty cycle will look brighter to > a human than an LED using 0.5A continuos. =A0Correct me if I am wrong. You're wrong. At 50% duty cycle an LED will definitely look dimmer than the same LED run at half the current and 100% duty, as this effect doesn't happen at all. Chris -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist