[sdiy] Re:

[Brock Russell]

>LEDs running at low currents will operate in an area where brightness
>differences
>are very obvious.

True

>By pulsing them at a higher current, the eye is fooled into
>thinking
>that the LEDs are brighter, and the physical limits of the LED are overcome at
>the
>same time.

?? The LED is operating in a preferred forward current range and the LEDs 
ARE brighter.

>The eye sees the flashing LED as brighter than the average... it is
>more of a peak detector in that regard.

This is a myth. The eye averages.

To quote a more knowledgeable source than I,
"The Talbot-Plateau Law states that if a light is rapidly flashed,
at a rate so that it appears fused to the observer, the light will
match in brightness a steady light that has the same time-average
luminance."

Why this myth persists, especially among us electronics guys who
have been working with this stuff too long, is that old style LEDs
have a non-linear current-luminous intensity characteristic so
driving them at 100mA and a 10% duty cycle might result in the
apparent intensity of the LED being driven continuously at 20mA
rather than the expected 10mA. This is not due to averaging, it is
due to the LED being 20 times brighter at 100mA than at 10mA.
(The numbers here are not realistic but get the point across).

Super bright LEDs such as GaP and AlInGaP are non-linear too
but drop off a bit with increasing forward current.

FWIW, I work with LEDs way too much...

Brock