In article rqqtj.374$we5.136@trnddc02,
James Sweet wrote:

"Dave Plowman (News)" wrote in message
...
In article ZSjtj.725$0%3.218@trnddc06, James Sweet
wrote:
They're pulse driven to give multiple brightness levels. Low as
markers, then they get bright when the brakes are activated. It has
nothing to do with increasing the max brightness.

Eh?

What?

The lights I'm talking about are used in lieu of twin filament
incandescent lamps for tail/brake lights. These have two brightness
levels, and to achieve that with LEDs they use PWM dimming to give two
levels.

They may well but the primary reason is to increase the brightness.
Pulsing allows the continuous current rating to be exceeded. And necessary
with most common LEDs if you need to near match the output of tungsten for
brake lights etc.
To alter the brightness on an LED all you need to do is change the drive
current. Doing it via PWM is more efficient - but that really doesn't
matter with car indicator lamps.

--
*Can vegetarians eat animal crackers?

Dave Plowman London SW
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