This is topic dimming projector bulbs in forum Film-Yak at Film-Tech Forum ARCHIVE.


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Posted by Pravin Ratnam (Member # 1417) on 03-25-2006, 07:35 PM:
 
I often read how theaters often cheap out by dimming their projector bulbs in a misguided attempt at saving the bulb's life.

I am just curious. How do they dim them? Is there a dimmer switch or control? I thought the bulb was just turned on and off. And if there is a control for the brightness, why would theater management feel compelled to dim them? Do they really think they are saving much money?

Also as the light bulb's lifespan dies down, is there a way to crank it up to compensate for the dimmer light or does it just stay bright all the way until it dies.
 

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Posted by Steve Scott (Member # 630) on 03-25-2006, 10:21 PM:
 
Lamphouses have current adjustment controls that vary the output of the lamp. New lamps require lower current settings during the beginning of their run. Lamphouses have hour meters that allow booth personel to keep a record of how long a bulb had been running & to serve as an indicator to increase the bulb's current as needed through its life to maintain at least 16 fL of screen illumination & proper bulb focus. Some cheap theaters maintain this setting well into the bulb's life, making the image appear darker, but theoretically allowing the theater to go longer without changing the bulb.

This is usually only theoretical, though, because if a theater feels the need to be so neglectful it's likely that much attention may not be paid to other aspects of lighting & film operation in general, causing shortened equipment life & other costly issues (not to mention the drop in ticket sales because your films are dim & fuzzy at the edges).

Usually, this kind of poor presentation occurs in theaters where only the manager or one other staff member has been questionably trained to service booth equipment & just can never get around to even taking a look at the illumination, let alone focus of their bulbs. But there are also plenty of neon-covered megaplexes that don't put bulb alignment on their priority list. Lots of these places just wait for service calls from contractors or their parent companies to even take a look at the bulbs. Some chains won't even allow booth personel to make any technical adjustments.
 

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Posted by John Pytlak (Member # 331) on 03-26-2006, 03:04 AM:
 
I wrote about this years ago:

Let There Be Light

quote:

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Sometimes, the problem was misinformation. For example, many theatre
managers believe you save money by running a xenon bulb below its rated
current. In reality, although this may save a little electricity, it may actually
shorten the life of the very expensive bulb. If the quartz envelope of the bulb
runs too cool, deposits will form, blackening the bulb.

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quote:

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Twenty years after I first wrote about this problem, many movie theaters continue the insane practice of dialing down the intensity of projector lamps under the mistaken belief that they can reduce their power bills and extend lamp life. As a result, many movies are projected so dimly that their impact is diminished. I've quoted Eastman Kodak experts who say the light level has no effect on bulb life.

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