Re: (ET) Ralph's LEDs

[William Korthof <wkorthof earthlink net>]

David,

I'm friends with the owner of one of the most established LED traffic
signal retrofit manufacturers, and I've been following progress with
them for 10 years. Every production unit I've seen uses some form
of current limited power supply designed to approximates a
constant current supply (with varying effectiveness). Where did you
get the information that a pulsed power supply is common?

/wk

At 09:53 AM 11/22/2003, David Roden (Akron OH USA) wrote:
> I recently read something fascinating about LEDs.  Have you noticed how
> intense the new LED traffic signals appear?  (At night some are so bright
> that the green ones actually are almost painful to view.)
>
> This is how it's done.  The LEDs are driven by a pulsed waveform.  The on
> current is TEN TIMES their rating, but the duty cycle is only 10% - that 
> is,
> on (for example) on 1 picosecond, off 9 picoseconds, repeat.  Thanks to
> persistence of vision, the human eye sees the peak intensity as continuous
> high intensity; but the LED "feels" the average current, which is just its
> normal rated current.
>
> I'm sure the same thing could be done with automotive signals (if it isn't
> already).
>
> Clever, no?
>
>
> David Roden - Akron, Ohio, USA
> 1991 Solectria Force 144vac
> 1991 Ford Escort Green/EV 128vdc
> 1970 GE Elec-trak E15 36vdc
> 1974 Avco New Idea 36vdc
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>
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