P3D Re: Halogen bulbs for projectors

[Tom Hubin <thubin@xxxxxxxxx>]

dalia miller wrote:
> 
> At 02:39 PM 2/17/00 -0700, you wrote:
> >Dalia wrote:
> >
> >>All the above named projectors can use halogen bulbs that
> >>provide a little more lumens (about 10%) and a much longer
> >>life than the CZX bulbs...
> 
> George wrote:
> >My measurements showed that the halogen bulbs actually
> >resulted in less lumens in both my 116 and 716 stereo
> >projectors.  

> Dalia wrote:
> George, it might be interesting to see how you tested.  Let us know.  I
> didn't do any scientific testing on the bulbs output because I just don't
> have the knowledge nor the equipment.   I'm just reporting what the bulb is
> rated for.  The 500w halogen bulb has 13,000 lumens; incandescent has
> 11,000 lumens.  The 750w halogen bulb has 20,000 lumens as opposed to the
> incandescent's 18,000.

I did a simple demo at a PSSP meeting last year. No meters used. I put a
new CZX 500W and a new BTP 750W in a TDC 116 projector. Then projected
an empty slide mount onto the white wall about 3 feet away. I blocked
one projection lens at a time and let folks vote on which side was
brighter. The difference was obvious and all chose the 500W as brighter
than the 750W. The next half hour or so was devoted to lecturing on how
the lamp filament, condenser optics, slide, and projection lens aperture
combine to give the brightness.
 
>   I did do some very primitive testing a while ago with a Stereomatic 500
> after I changed out the mirrors (didn't change the condensors) and replaced
> the polarizers in each projector.  We measured the amount of light that
> bounced off the screen with one of Andrew's fancy fancy light meters - and
> the halogen bulbs produced a slightly brighter image.  It was not
> appreciably brighter and I can't remember how much more candle power was
> detected.
> 
> My conclusion at that time was:  the halogen is only slightly brighter but
> the bulb's  longevity made the bulbs much more desirable.  Please note that
> I didn't test the bulb's longevity myself, we used the specs for the bulb.

My conclusion is similar to yours, although I could find no suitable 500
watt halogen lamp at that time. What I concluded was that the
substituted 750 watt BTP produced about 50% more heat and over 50% more
light than the original 500 watt CZX lamp. The extra heat was damaging
slides due to inadequate heat absorbing glass. The extra light was not
making it through the projection lens because the BTP filament was so
much larger than the CZX filament.
   
The condenser optics is such that the 33mm diameter of the projection
lens is imaged onto the filament as a 10mm diameter circle. This is like
having a 10mm diameter aperture at the filament. Any part of the
filament that is outside this 10mm diameter cannot contribute any light.
The TDC116 condenser optics was designed with an 8mm square CZX filament
in mind. Too much of the light from the 10mm X 14mm BTP filament is
clipped by this 10mm diameter circle.

When making substitutions, keep in mind that increasing wattage usually
results in proportionately increased heat. Increasing lamp wattage,
without dissipating the extra heat, is not a good idea if you value your
slides.

If the replacement filament is larger then the system is designed for,
you will lose light at the projection lens. This is not harmful but can
account for surprising light losses. This is what happened with the CZX,
DDB, and BTP lamps. We expected the BTP 750W to be brighter than the DDB
750W, or at least the same, but it was actually dimmer than the CZX 500W
lamp.

I am curious about the filament dimensions for the 500W Halogen that
Dalia sells. Can somebody measure it with a simple metric ruler?

It is curious that I had to speak to factory engineers to get the
filament dimesions or measure them myself. That data seems to be
unpublished. It is no wonder that folks ignore that when making
substitutions. Yet it is just as important as the other data.

Here is data that I got from both GE and Philips for the incandescents
and just from Philips for the halogens. I measured filament dimensions
with a mm ruler. All have Medium Prefocus base with filament centered
55.5mm from top of base fins. 

ANSI, Type, Elect Power, Light output, Color Temp, Lifetime, Filament
Dimensions

CZX, Inc, 500W, 12500Lum, 3200K, 25Hrs, 8mm square
DDB, Inc, 750W, 19500Lum, 3250K, 25Hrs, 10mm square
BTP, Hal, 750W, 21000Lum, 3200K, 200Hrs, 10mmHoriz X 14mmVert rectangle
BTN, Hal, 750W, 17600Lum, 3050K, 500Hrs, unknown
BTL, Hal, 500W, 11000Lum, 3050K, 500Hrs, unknown	

Tom Hubin
thubin@xxxxxxxxx