On Thu, 06 Jan 2005 08:25:29 -0800, Bill Turner
wrote:
What other reason could there be?

Hi Bill,

The usual reasons: Brighter; Lower Power; Longer Life; Lower Loss - as
long as the added complexity is offset by the economic gain. If they
were dual diodes connected parallel and reverse polarity driven by AC,
then the advantage would be reduced cathodic reduction of contacts
exposed to water (for years I noted how the poorly built US cars went
through tail lights that burnt out due to corrosion). AC systems also
extend lifetime to conventional filament lights.

Now, by Brighter, this is not due to higher peak currents. LEDs don't
really peak as well as other devices. Their overdrive capacity is
somewhat limited. Rather, the Brighter is a physiological response.
It is actually the same brightness, except we perceive it as brighter
(although, if the period exceeds the Stroud Moment this may no longer
hold). Light can be frustrating to compare to measurements, because
impartial measurements will reveal little difference to what we
perceive to be dramatic change. One of those tricks of the brain.

73's
Richard Clark, KB7QHC