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Topic: dimming projector bulbs

Pravin Ratnam
Jedi Master Film Handler

Posts: 844
From: Atlanta, GA,USA
Registered: Sep 2002

posted 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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Steve Scott
Phenomenal Film Handler

Posts: 1300
From: Minneapolis, MN
Registered: Sep 2000

posted 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. [Frown]

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 03-26-2006 03:04 AM

I wrote about this years ago:

Let There Be Light

quote:
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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Ian Price
Phenomenal Film Handler

Posts: 1714
From: Denver, CO
Registered: Jun 99

posted 03-26-2006 03:19 AM

This pisses me off! Roger Ebert complains about this constantly in his Movie Answer Man column on the web.

He states:

quote:
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.

Movie Answer Man

Perhaps one manager turned the lamp down, but the majority of the light problems is due to deferred maintenance. Either the manager doesn't notice that the lamp is double the guaranty or the head office refuses to buy him a new lamp. The end practice is the same, the film is presented a substandard light level, but the cause is different.

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Pravin Ratnam
Jedi Master Film Handler

Posts: 844
From: Atlanta, GA,USA
Registered: Sep 2002

posted 03-26-2006 01:58 PM

I was on a trip to India and England in February. In India, I was in a small city called Vijayawada near Hyderabad in Southern India. I went on a tour of theaters and the quality has gone down since the last time I went there - 8 years ago.
All the movies seemed out of focus and not bright enough. But the out of focus stood out. One theater had decent projection and they made a big deal they had 70MM and a Zenon projection system. Even this house was merely decent. The other theaters I went to (usually two theater complexes), the projectionists usually blamed the carbon arc bulb.

In England, I went to Bath and saw Lucky Number SLevin at an Odeon multiplex(talking about converting your ticket prices into dollars. nearly 14 bucks!). This theater seemed new and it was pretty good brightness and the image was in focus.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 03-26-2006 06:44 PM

My Kodak article was based on information that people that took the Kodak "Film Projection for the Reel People" projection seminars brought forward. There was often a misunderstanding of how to extend xenon lamp life, maybe based on experience with dimmed tungsten lamps in theatres.

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