From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 10/24/01-04:30:18 PM Z
At 09:32 AM 10/24/2001 -0600, you wrote:
>
>Sam,
>
>No problem with getting the rods. Apparently they are the same as sold in
>welding stores and are still used in movie projectors in outlying areas.
>
>Here is an interesting article I found. It looked like it was worth the
>band with to send to the list:
>
>Carbon arc basics:
Tons of snipping.
A brief addendum. The carbon arc lamps used for motion picture projection
and for studio lighting are not pure carbon. the positive carbon is hollow
and filled with a mixture of rare earths. The idea is to creat a luminous
plasma which is responsible for most of the light output. The exact mixture
of material in the core controls the spectrum. Projection carbons have a
target color of 5400K. The arc mechanism must both feed the carbon and
rotate it for uniformity.
For projection most carbon arc has been replaced by Xenon arc lamps,
which are much more uniform and don't require any mechanical devices to work.
Xenon arcs are being used in motion picture production but there is still
considerable use of large carbon arcs, especially for boosting daylight.
Xenon arcs were adopted for production in Europe long ago. Xenon has a
higher effective color temperature than daylight carbon so requires some
filtering when used for lighting color.
Non-filled carbons have relatilvely low color temperature and efficiency.
High pressure Xenon arcs require safety protection since the lamps can
explode quite violently.
---- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com
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