Electronics > Projects, Designs, and Technical Stuff
Human Eye -- Peak or Average Response
Audioguru:
I was taught that a fast pulse or pulses of light for durations less than 30ms appear to be dimmed. I am not talking about a slow incandescent light bulb.
Nusa:
--- Quote from: jweir43 on June 09, 2019, 09:14:36 pm ---Sorry, I though it obvious that I would have to get over the 24 Hz. flicker frequency to avoid the persistence of vision obstacle. Let's say that you have your choice of any frequency from 25 Hz. to daylight.
Viewing angle is dead on boresight.
Empirical testing to follow. It is a trivial experiment and one that I probably should have done instead of asking the question if anybody has done the experiment and how did it turn out?
Let me pose the question for what I **REALLY** want to know.
I've got a white landing light of about twenty watts (DC power). I shine the light at the ground when I'm about 350' AGL. It lights a rough ellipse on the ground and lets me see whether or not there are animals on the runway before I collide with them.
I run the light on DC and get a particular illumination. If I run the same exact device on AC of any frequency you want above the flicker level and I adjust the current so that the pulse width times the current gives me the same power into the light, will the light appear brighter to me as reflected from the SAME ground at the SAME altitude at the SAME attitude, at the SAME .... In other words, the only differences is pulsed power versus DC. Does the pulse width affect the result (right up to the maximum pulse current of the device)? Is it any brighter at any combination of pulse width and current than at DC?
THat should take care of any test conditions, I hope.
Jim
--- End quote ---
24 Hz may give you persistence of vision, but flicker is easy perceived by just about everyone. Still, even that was pretty amazing to people early on in the moving pictures industry. These days it's upsampled for display, unless you want the old-time effect on purpose.
RE 20 watt white light. If it can run on AC or DC, we're not talking LED's anymore, are we? Most likely we're talking incandescent and the theory of operation is completely different. The light comes from the filament being HOT enough to glow, which is directly related to power applied. It takes a LOT of time (relative to an LED) to cycle between ON (HOT) and OFF (COOL), so the filament itself has persistence of temperature that will largely mask frequency effects.
Also, this is a completely different question. The original question was how bright does the LED appear. The new question is how effective is a light being cast while moving at high speed. I can't really answer that, other than to imagine that any sort of perceptible strobe effect could be very bad indeed, both because it's annoying and because you might miss something on the ground.
jweir43:
Oh, dear God.
I can buy 50 watt LEDs if I can figure out how to heat sink them.
Your stuff about moving light sources and propeller sync have NOTHING to do with the question. The LED is WELL outboard of the propeller. PLEASE do NOT introduce extraneous problems as there are none.
You want a clean airframe? Same problem; consider a glider.
Sheesh
Jim
jweir43:
Please, just GO AWAY.
Thanks,
Jim
jweir43:
--- Quote from: Audioguru on June 10, 2019, 12:40:07 am ---I was taught that a fast pulse or pulses of light for durations less than 30ms appear to be dimmed. I am not talking about a slow incandescent light bulb.
--- End quote ---
You were taught wrong.
Jim
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