BH> The *istDS allow me to adjust the white balance to the lighting,
BH> holding up a white or gray card before the camera etc. Hopefully,
BH> this will work even with leds!
For some high power LEDs, try Lumileds - I am trying to get some
locally for use in a flashlight.
One particular problem in photography with LED lights could be the
spectrum - Tomasz mentioned that white leds _are_ continuous spectrum,
but if the spectrum differs (as he says) a lot from daylight, ie it
has peaks at different wavelengths and god knows what phosphors they
use, nobody yet mentions Colour Rendition Index in their product
brochures for LEDs (although they may publish some spectrum diagrams
which you could compare with daylight) - digital cameras cannot adapt
to much differing light sources, just because they are RGB devices
with factory set filters and white balancing is done by
multiplying/dividing R and B channels relative to G, plus some hue
adjustment. This won't get you good balance _if_ the LED phosphor
spectrum differs considerably from daylight... At least I think from
my meager understanding of the matter. For example, if the spectrum
has a significant peaks in just some wavelengths, you would have
to use some special filters to diminish these wavelengths. And with these
cheap white LEDs you can almost bet on their phosphors being not
daylight white, just like with cheap fluorescents. Or perhaps not :)
But most white LEDs have significant colour difference at the edge of
the beam - with most going to strange yellow - this would affect the
colours considerably.
For some more information, try looking at the Lumileds.com site, and
also search for LEDs in enlarger heads - several darkroom geeks have
converted enlarger heads to LED lighting, although most probably just
for B&W where the colour response is not so demanding... But it
could give you more starting points. There are definitely LEDs with
phosphors with excellent spectral charasteristics, as LEDs are used as
backlighting for the newest 6000$ a piece LCD DTP displays (NEC,
EIZO)...
Good light!
fra
