> >- Their claims re colours, colour change with time, light quality and




> >similar between CFLs, LEDs and ESL are extremely suspect. You can make poor
> >low life poor spectrum CFL and LED products. Or, rally very good ones. ESL
> >relies on phosphor luminescence and their claim re better spectrum would
> >need to be checked. A modern phosphor LED DOES have a poor two peak spectrum
> >due to the mixing of the LED blue with phosphor yellow - but better can be
> >achieved. Recent moves to higher power RGB LEDs in commercial use and you
> >could easily go to 4 emitters if desired.

> The human eye does an auto color balance anyhow. Photographs can be
> misleading.

Yes.
When I want to do lighting comparison photos I have to adjust the
camera to show what I see and not what it thinks is really there.

BUT a significant number of people complain that CFLs and/or LEDs and
also some gas discharge lamps (eh high presure metal halides) cause
them visual problems.
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. While the eye will see this as "white" if the vector sum
of the energies on a color diagram (CIE1931 or whatever) lies close
enough to the black body line, this does not mean that everyone will
feel good about what their brain is telling them. An incandescent bulb
produces a far more continuous spectrum. LEDs could have multiple
phosphor colours if they chose to to improve this effect. I'm not
aware that this is done (although it almost certainly is) and
economics and efficiency probably feature in decisions.

> What kind of LED lamps are you using? The LED elements are getting quite
> high in power (>100W), but they are still pretty pricey. Still-- LED
> streetlights are now possible.

Small ones :-).
My interest is focused (pun noticed) on LEDs < 1 Watt at present.
As it is about to appear on the wbsite along with more descriptions
and better pictures I imagine that it's OK to say that the light at
bottom right at http://www.bogolight.com/ will have "Nichia inside".
At 120 - 140 lumen / Watt it will be as efficient as anything I've
seen available commercially. People keep telling me that there are
better LEDs around but I've yet to see a product running 120 l/W+ for
sale. Yes - PLEASE DO provide website references. The basic light is
simple but hopefully very very useful. Genuinely waterproof in any
sensible use. Drop test shock performance to in excess of Mil Std 810G
(lots of fun). Depending on future directions I may get to put ... -
but then you'd have to kill me :-).

___

The top LED makers can make good LEDs. But almost all the rest make
junk. And I haven't found the others yet, alas. Getting a small LED
that works with reasonable lumen maintenance for > 10,000 hours is a
challenge. Most people don't need > 10k hours, but if you do you
should choose your LED suppplier extremely carefully.


            Russell
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