Pulsed illumination and perceived brightness

Factual Questions
1

I read something on some electronics site or other (I can probably find it again if anyone is interested) to the effect that a pulsed light source with a total of 50% duty cycle, provided the frequency was high enough, would appear just as bright as a constant one, while using only (about) half the energy (assuming perfect square waves and perfect linear emitter with instantaneous response etc etc).

It sounds like bunk to me; after all the total output in terms of photons is halved, we would just perceive it as half as bright, wouldn’t we?

2

I don’t think it’s bunk; I’ve actually employed such a technique before to extend battery and LED life. I don’t know the physics behind it though.

3

I don’t doubt that it would extend battery life; it’s the biology rather than the physics that baffles me; half the amount of photons is reaching the eye, but is causes the same amount of stimulation?

if this is true, is it perhaps because the ‘dark’ phase of the cycle is happening while the rods/cones are ‘resting’ after having received a stimulus?

4

When a light bulb works the filiment is so hot, small pieces come off. Since the wire takes time to cool down. As long as your off time is short enough, the wire should still fizzle in about the same way.
(There is a word for that fizzle, I just don’t remember it)

Lumens are not directly porportional to RMS or even average voltage.

I dunno if it’s bunk or not, but it sounds possible to me.

5

danvanf, are you perhaps confusing “incandesce” with “effervesce”?

6

Na but I am reading Incandecent light rather than light source.

7

http://www.caves.org.uk/led/foot4.pdf

Sounds reasonable to me.

8

While reading a printed article on telescope eyepiece design, I ran across the curious claim that a 50% decrease in the brightness of an image from the center to the edge of vision is not normaly perceptible. That sort of visual filtering might leave room for some slop in the actual versus percieved brightness of pulsating illumnation.

9

well… i have a ‘night light’ by the guys at color kinetcs www.cksauce.com that uses two sets of rgb leds set end to end and run with varying pulsewidths (thats what they said) to use less energy and create all colors in the spectrum including white…

if you are talking about lighting large spaces though, i think flourescent lighting is still the best option right now… cfl lights for your house last longer and use mostly 1/4th the energy of normal lightbulbs…