Electronics > Projects, Designs, and Technical Stuff
Human Eye -- Peak or Average Response
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tooki:

--- Quote from: TheUnnamedNewbie on June 12, 2019, 08:20:06 am ---Another strange thing with PWM at low-ish frequencies is that you might not notice when it is still, but really can notice when it moves. This is, after all, what those rotating-stick-of-LED displays are based on. Easy way to notice: Just have an LED PWM at a few hundred Hz and then shake it violently, and now notice how you see dots instead of a line of light.

--- End quote ---
That’s the phantom array effect I mentioned earlier in the thread.
bsdphk:
Ok, found the HP35 reference, and it does not argue for peak sensitivity:  http://hpmemoryproject.org/timeline/dave_cochran/a_quarter_century_at_hp_00.htm

"We decided to use an inductive driver for the LEDs to store energy and to get the high currents. We had heard that super-linearity would get more light output than just proportional. I talked to the LED guys at HP Associates, "What happens if you pulse these? Can I pulse them with 1,000 amps?" "Oh, no, 1,000? No, no, no." No, we're talking about milliamps." "Oh, well, okay." The average current on the LED segments was something like three or four milliamps. And I said, "Well, suppose we hit them with 30 milliamps, but 10 percent duty cycle?" "Oh, well, that might work." We actually ended up with a one percent duty cycle. Got about three times the light output than we would have if we'd just applied the three milliamps. We put 300 milliamps through it, at one percent duty cycle. Got three times the light output; now that's a freebie."

"Somebody asked about reliability. I set up an array of constant current three milliamp displays and compared them to in a set at a 0.1 percent duty cycle, ten times more than our design. I ran those for six months. And then I looked at the comparable light output over time. They were the same. […]"

HP Application Brief D-004 about LEDs (5963-7073) explicitly say they eye averages when using multiplexing.
Circlotron:
In the days before high power white LEDs I often wondered if you could use a xenon strobe lamp to make a decent spotlight and have the eye perceive the peak brightness. The average would have been nothing special.
Dubbie:
I’ve studied this area quite a lot in relation to my career and from my point of view, Tooki and Siwastaja have explained everything spot on.
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