Archived posting to the Leica Users Group, 1997/02/05

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Subject: Re: Leica slide projector
Date: Wed, 5 Feb 1997 11:56:08 +0100

Stefan Kahlert wrote

>   I several times read something about a certain projector throwing 
>   more or less heat out of itself. I seriously doubt such comments and 
>   think this is just a subjective impression. 

>   Every bulb produces a neglectible ratio of light compared of the more 
>   than 95% of heat that come out of the 150 or 250 W.
>   The projector must get rid of this heat anyhow and throws out hot air 
>   accordingly. It doesn't matter it it throws out large amounts of 
>   modestly warm or small amounts of burningly hot air. The energy that 
>   is added to a rooms air-volume remains the same and so does the actual 
>   rise in temperature.

>   A 150 W projector produces nearly 150 W in heat a 250 W projector
>   produces 250 W. The rest is purely subjective.
>   Or am I getting something totally wrong?

>   best regards

>   Stefan
>   --
>   Stefan Kahlert, 
>   Medizinische Poliklnik der Universitaet Bonn


you are right, that most energy is turned to heat, not to light.
However there are two things to consider

1. The luminous discharge lamps (I just looked it up, since yesterday I
did not know the English word for 'Kaltlichtlampe') seem to have a better
light/heat ratio.

2. The overall heat does not bother me, it is the heat at the slide, and that
differs a lot from one projector model to another.

More heat at the slide means a stronger 'plop-into-position', and is probably
not desirable, if you leave your slides a bit longer in the projector.
When using the CF lens on glassless slides I enjoy the moment most, when the
slide plops and becomes sharp to the edges.