P3D Re: P3d projection

[jacob@xxxxxxxxxxxxxx (Gabriel Jacob)]

>I just did a heat damage study using 3 TDC stereo projectors. Please
>read my report at
>http://www.clark.net/pub/thubin/aosd/photo3d/ir_study.txt . Reader
>comments are welcome.
>
>Tom Hubin

I just read the report and it was very informative. Dr.T had
conducted similar tests and drew similiar conclusions (if I
remember correctly).

>Bill Duggan's projector is a TDC716 with SN A02882. It has a 
>pair of 3mm thick, almost colorless, infrared filters. The glass 
>type is unknown. The surface is encrusted with white particles
>that appear like table salt. The particles do not dissolve or
>soften in water, alcohol, acetone, or vinegar. I have been told
>that it is likely to be phosphates drawn from within the glass
>over the years.

That would seem to be the case. In an old Schott catalog I have, 
it mentions, under special remarks:

THE HEAT ABSORBING GLASSES of the KG-range contain a high
percentage of phosphoric acid and, therefore, have only a limited
weather resistance. Roughly polished glasses supplied by us are
usually toughened and protected against weathering if the
dimensions permit. In case these glasses are not ordered in polished
state, customers are requested to toughen them and to provide a
protective coating against weathering.

Since your paper overall strives for accuracy in terms and
concepts, I'd like to comment on some other points.

>I calculate that a typical projector lamp with a filament color 
>temperature of 3200K will convert about 9 percent of the 
>electrical energy consumed to visible light, 90 percent to 
>infrared light, and 1 percent to ultraviolet light. All energy 
>absorbed by the film will be converted to heat. It is 
>unavoidable that the visible energy absorbed is converted to 
>heat. 

Actually, not all the energy will be converted to heat. Varying
degrees of light energy will be transmitted and illuminate the
screen. If all the energy was absorbed and converted to heat the
screen would be black! Also strictly speaking, infrared and
ultraviolet energy is not light since it is invisible. Therefore,
the term "visible light" is redundant. 

>The infrared absorbing filter is often referred to as heat 
>absorbing glass. This is a misnomer. The glass absorbs infrared 
>energy and radiates heat. The notion is that it took the heat 
>away from the film.

The glass absorbs infrared energy (as you mention), but it
doesn't radiate heat but rather infrared energy. Something that
"radiates" is of electromagnetic nature. As you mentioned earlier,
infrared energy is not heat. The main reason the surrounding air
temperature increases is because of the conduction path of the
heat from the glass to the air.

Gabriel

  



        


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