Re: Color temp of lamps in projection

[P3D Gregory J. Wageman <gjw@xxxxxxxxxx>]

(Sorry about the garbled message.  My connection to my ISP was severed
while I was composing this reply, and for some stupid reason the mailer
transmitted it as-is.)

Dr. T. replied:

>> If you experiment and remove the polarizing
>> filters from the projector you will have the impression that the
>> the light gets "whiter" and the slides look better.

And Paul Talbot countered:

>I don't think "snap" is really what I am looking for.  Sometimes
>when the viewer button is depressed part way the bulb does not
>light up completely, but that reduced intensity seems to increase,
>not decrease, the golden/orange glow of the scene.  So the effect
>seems reversed with the projector.  Why the difference?

As was already mentioned, dimming of a viewer lamp is done by reducing
the voltage, which also reduces the color temp.  In this case the
poor contact's additional resistance performs the same function.

The polarizing filters on a projector act essentially like neutral-
density filters; that is, they reduce the visible spectrum pretty
much equally.  Thus they don't affect the color temp.  Polarizing
filters ARE available in blue-blocking "brown" color, which ought
to warm up the light considerably (I'm not sure if this would be a
good thing or not; haven't tried it yet).

By the way, for those (like me) who REALLY like the look of "golden
hour" (the hour after sunrise and before sunset), you will probably
HATE the look obtained on a brightly-overcast day (uniform thin layer
of clouds).  I was quite surprised to learn that the color temp. can
reach as high as 10,000 degrees Kelvin and more on such a day.  I find
it a very unflattering light.

Here's a related question: should one ideally be matching the color
temp. of the viewing light to the color. temp of the taking light, OR
is the original scene more naturally reproduced with viewing light of
a particular, fixed color temp., and if so, what temp. is ideal?

	-Greg W.


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