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Old 16th Jun 2019, 11:25 am   #101
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Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 812
Default Re: Turntable Stroboscope

Originally Posted by GroovyG View Post
Regarding the perceived brightness of the LED, there's a phenomenon whereby a short duration flash is seen as being brighter than one of longer duration, even of the the same actual brightness. It's too long now since I was an optometry student, and I've gone off in altogether another direction since, so the details now elude me, but I'd expect a 208μs flash to be comfortably in the relevant range.
Thanks GroovyG - another optometric phenomenon I've learned about today!

Looking back at my Post #60 above where I did a quick calculation that we want the LED to be on 1/16th of the time which is 3333μs divided by 16 (or multiplied by 0.0625) = 208.3125μs.
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Old 16th Jun 2019, 10:23 pm   #102
Join Date: Nov 2015
Location: Witney, Oxfordshire, UK.
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Default Re: Turntable Stroboscope

Of course, flashes at 300hz are well above the eye's critical fusion frequency - that at which individual flashes cease to be distinguishable - which itself varies according to stimulus brightness and retinal location. (Thus, you'll have noticed that the flickering end
- 50hz at the ends - of an old fluorescent tube is much more apparent in peripheral vision than when looked at directly.)
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