Re: Projection lamps

[P3D Greg Erker <erker@xxxxxxxxxxxxxx>]

Allan Woods asked:

>[a bunch of questions I don't know the answers to. deleted]

>Another frame of reference is: If you were going to make a projector
>from scratch, how would you choose a light source? (...other than
>cost, broad availability, transformer requirements, etc...)  ...or
>are those too many restrictions?

  I have heard that for household lighting low voltage halogens
(12V I presume) are more efficient than 120V halogens, despite
having a step down transformer that isn't 100% efficient.

  The reason stated is that 12V is a more appropriate voltage
for the characteristics of the tungsten filament. At 120V the
filament has to be made very thin and long to get the resistance
high enough for the desired current. The low voltage filament can
be more robust and thus run at a more efficient temperature.

  Don't know if the above is true, and how much of it applies
to projectors. Supposedly the FED projector that Joel sells
is brighter than an old 1000W projector (it uses 24V halogens).

Greg E. in Saskatoon, Saskatchewan, Canada

Bio and photo at:
http://www.sask.trlabs.ca/trlabs/grege.html



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