From: Spehro Pefhany
Subject: Re: LED flickering problem
X-Newsreader: Forte Agent 1.92/32.572
Date: Mon, 23 Dec 2002 15:09:37 GMT
NNTP-Posting-Date: Mon, 23 Dec 2002 10:09:37 EST
On Mon, 23 Dec 2002 14:33:19 -0000, the renowned "John Jardine"
>Unless you have an incredibly high visual response speed, then a refresh
>rate of even 20Hz would be sufficient.
NO.. 20Hz is WAY too slow. Try it (with a numeric display) and see.
But 80Hz is acceptably fast, with double that being pretty darn good.
>Sounds like the LEDs when in the 'on state, are not being given enough drive
>current to produce the intense, short, bright, flash needed to give the
>human eye a perception of continuity.
Drive current doesn't matter other than to establish brightness level,
there is no effect that is as you describe. The only flicker effect in
the human eye that I'm aware of is the better perception of flicker
in the periperal vision. Not a factor here.
>I.e. As you say, when static, the current is as it should be. But ... when
>being scanned, the current needs to be a lot higher to give more light out
>to balance the shorter time they are 'on'. Essentially the current needed is
>high enough to burn out the LEDs in the static unscanned condition.
It shouldn't be that high with conservative design practices- under
typical room-temperature conditions.
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