Russell McMahon wrote:
> I have noted that people seem to have problems with some system which
> they describe in terms which are iunrealistic - eg LED flicker from DC
> driven LEDs. HOWEVER the reality of a problem and the description of
> the effect do not have to correlate for the problem to exist. eg a
> white phosphor LED will usually have a blue and yellow peak, one from
> LED drirect blue and the other from phosphor excitation and
> reradiation.

I have a theory about that. Physiologically, the human eye actually has
virtually zero blue receptors in the area of the fovea* (the area of
highest resolution). The brain normally can compensate for this by
interpolating colors across this area. However, I can imagine that a
white surface illuminated with a combination of narrowband blue and
yellow sources may look white in the peripheral vision, yet yellowish
in the spot you're actually looking at. As you move your eyes around,
as in reading a printed page, this could be perceived as a form of
"flicker".

* There currently seems to be a (marketing) fad for blue LEDs in nearly
  everything, but using them as LCD backlights is actually a really bad
  idea for this reason -- especially in devices meant to be used in cars
  ... at night.

-- Dave Tweed
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