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From: jbm@eos.UUCP (Jeffrey Mulligan)
Newsgroups: sci.electronics
Subject: Re: LED refresh rate
Message-ID: <6815@eos.UUCP>
Date: 8 Jun 90 01:10:52 GMT
References: <30513@cup.portal.com> <61580@sgi.sgi.com> <30550@cup.portal.com> <21217@nigel.udel.EDU>
Distribution: usa
Organization: NASA Ames Research Center, California
Lines: 26

berryh@udel.edu (John Berryhill) writes:

>In article <30550@cup.portal.com> John_A_Pham@cup.portal.com writes:
>> 
>>     Ooops, I should make that clearer.  I want the refresh rate for LED
>>that a human eyes can tell between an OFF and ON cycle.  Heck, for 
>>1mhz or faster, LED will just fully lit to the human eyes

>Although the persistence of visual images depends upon intensity and
>color, 15 Hz is generally the point where you can't quite tell whether
>an LED is on steadily or flashing.

I would say more like 50 or 60 Hz.  This is why TV uses interlace:
although a 30 Hz frame rate is acceptable for sampling motion,
30 Hz flicker is unacceptable, so by displaying the even lines and
then the odd lines large areas have an effective flicker rate of 60 Hz.

BTW a previous post on this topic incorrectly stated that flourescent
lights flicker at 60 Hz; the flicker rate is 120 Hz since the lights
glow during both + and - phases.

-- 

	Jeff Mulligan (jbm@eos.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 262-2, Moffet Field CA, 94035
	(415) 604-3745