Re: Leica slide projector

[David Seifert <dseifert@earthlink.net>]

At 08:16 AM 2/5/97 +0000, 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?
>
>
Stefan:

A minor detail is that the Watt is a measure of electrical power consumption
not heat or light.  Not all 150W bulbs put out the same number of lumens. As
a consequence it is possible for 2 lamps which emit the same number of
lumens to consume vastly different numbers of watts. You are correct that
given a constant number of watts of power consumption the heat liberated
will be roughly the same. What you are overlooking is that image brightness
is a function of the number of lumens emitted by the lamp not the number of
watts consumed so a given system can produce equally bright images while
using substantially less power and producing less heat.

I believe that the 60W halogen light above my kitchen sink produces as much
light as a 150W incandescent yet only produces heat proportionate to the 60W
of power consumed.

Best Regards,

David Seifert
dseifert@earthlink.net