Re: [photo-3d] Projector Brightness

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

Don Parks write:

>I was very surprised that there was
>essentially no increase in brightness when using the 750 W bulbs.

I have found and reported the same conclusion!
>From a 1996 posting: "When I replaced the 750W bulbs
in my projector with 500W bulbs, I measured the same
light output, 6.2EV w/ASA 100" (I was using a digital
light meter and was making measurements at screen level)

>With the lowered (107 V) voltage my TDC 116 was only drawing
>960 watts and the fan was about 80 of the 960.  So both 500 watt 
>projection bulbs (total 1000 watts) were only drawing about 880 
>watts total.  This reduction in voltage makes a big difference 
>in the potential brightness of the projector.

Great!  I have found and reported the same conclusion!
Again from a 1996 posting: "I tried to measure the voltage
and current drawn during the operation of the projector.
I do not have my notes here but I remember that the
calculated Wattage (amps x voltage) was significantly
lower than the expected 1000W and 1500W (using the
500W and 750W bulbs).  Out of memory I'll say that
it was like 800W (instead of 1000) and 1200W (instead
of 1500)."

>To compensate for the lowered voltage I used a 
>variable transformer.  

Very good Don!

It will be interesting to answer these two questions:

1) Why isn't the light output increased when using
the higher wattage bulbs?

2) Why isn't the full wattage delivered to the bulbs?

Regarding #1 I think the answer is that the projector
does not utilize the full filament of the light bulbs.
Tom Hubin has posted a lot of details on this and
my testing confirms that (I will describe this test
in a future posting).

Steve Spicer has replaced the older bulbs with modern
24V/250W halogen bulbs (these are the same bulbs used
in the RBT projector).  Even though these bulbs have
HALF the wattage rating of the older 500W bulbs, they
produce a brighter image!  Steve reported that the
brightness of his TDC projector is the same as the
brightness of the RBT projector!  (In my measurements
at home, the RBT projector is brighter than the TDC.
I will measure and quantify the difference.)  

Why are these bulbs better?  Because they have smaller
filaments and all the light goes through the optical
system of the projector (this is not the case with
the old bulbs).

I have to go now... I have an appointment to do my
taxes! :)  More later...

George Themelis

 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/