Re: A bit more on projectors...

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Sun, 22 Dec 1996 22:21:03 -0600
>From: P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx>
>Subject: Re:  A bit more on projectors...

>...So to summarize,
>in regular tungsten lamps, the filament evaporates and becomes thinner as
>you mention and thus consumes less power. This lowering power consumption
>decreases the operating temperature and will shift the color to red. The
>light output decreases because of bulb blackening and also the lowering
>filament temperature as mentioned. 

Thanks for the additional information.

>On a slightly different note, it's interesting that the Stereomatic
>uses one 500W bulb. Intuitively one would think that if it had used
>two 500W bulbs, the output would be twice as much in each side, but
>this is not the case. A pratical example of this is, one 100W light
>bulb is more efficiant than two 50W light bulbs and will give more
>total light output than the two. Of course in the stereomatic there
>are probably other light losses introduced by the mirrors and light
>path. 

I suppose it also helps prevent uneven light output from bulbs that are
not well matched or that are of different ages.

It would sure be nice (at least for projectors that put the polarizer 
before the slide anyway) to be able to split up the polarization of the
light at its source, and send the differently polarized light down the
two optical paths, instead of having to soak up about half the power of
the visible light beam using polarizing filters. [Maybe some trick
involving birefringent material, half-silvered mirrors, etc.]

Such devices appear to be used in some optical instruments - I don't know
whether the efficiencies, power handling capability, etc. would make this
approach attractive for stereo projectors.

John Roberts


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