Re: Best way to power array of LEDs?

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#231

From: Winfield Hill
Date: Mon, 07 Oct 2002 12:42

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"James wrote...
>
> The traffic light LED's use a transformerless power supply usually
> so they flicker at 60 Hz, the yellow doesn't flicker because it's
> incandescent, they're on so little that the savings of using LED's
> for them would be minimal.

 Nope, shouldn't be so.  The usual bridge rectifier input makes a
 transformer-less storage-capacitor-less LED traffic-light run at
 120Hz, not 60Hz.  Surely that's what they use.

 Any LED traffic lights that pulse (I haven't seen any) may have been
 an early model, so designed in an attempt to take advantage of better
 visual sensitivity and the attention-getting nature of 5-to-25Hz
 flickering light, and possibly to be more easily distinguished from
 reflected sunlight.  But around here, all the LED traffic lights are
 so BRIGHT that sunlight isn't an issue; being blinded at night is! 

 Alternately, if you've only seen one flickering traffic light, I'd
 suspect it's defective.

 Thanks,
    - Win

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From: Winfield Hill <whill@picovolt.com>
Newsgroups: sci.electronics.components,sci.electronics.design,alt.engineering.electrical,aus.electronics,sci.electronics.repair
Subject: Re: Best way to power array of LEDs?
Date: 7 Oct 2002 05:42:40 -0700
Organization: Rowland Institute
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