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Posted by David McCall on 07/03/06 15:10
"PTravel" <ptravel@travelersvideo.com> wrote in message
news:Pl_pg.114414$H71.48097@newssvr13.news.prodigy.com...
>
> Sodium lights contain impurities, so the output isn't a perfect 589 nm --
> otherwise you could use it as a laser. If you put the output through a
> spectrum analyzer, you'd see a sharp spike at 589nm, but there'd be
> fall-off on either side of it, i.e. though most of the light output is at
> 589nm, there may be light output as much as 10nm (or whatever) on either
> side of it.
>
Have you seen a spectrum anaylisis that shows this "falloff"?
It's been a long time since I've seen one, but I seem to remember
a chart with a a tiny bit of noise at the baseline, and the spikes
were just thin vertical lines. They once used sodium vapor lights
to light the background for process shots. It seems strange because
the orange spike of the lights is so close to the colors in flesh tones,
but they were still able to pull a matte. It is quite "pure".
Flourescent lights also have these extremely narrow spikes, but the
phosphers added to the inside of the tube produce a glow with a
wide enough spectrum to allow you to see colors. Depending on
the phosphers used, the color rendering quality will be of better
on some lamps than others (usually tracks with the price of the bulb :-).
David
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