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Personally, I prefer to leave exciter lamps on whenever the theatre is open. My reasoning for this is failures usually occur when the lamps are first powered on and that I would rather not have one burn out right at show start or at a changeover. In practice, though, failures are pretty rare.

I don't like exciter-lamp changeover systems, either, since they have the additional problem of causing a second or so of silence at every c/o while the second lamp comes up to full brightness. I find this very noticeable and distracting (especially when combined with a 'pop' at every c/o, which seems to happen in way too many older theatres).

This is a common trick also used by every stage lighing equipment. It allows the filament to stay warm, but dark. Since the filament is warm, it will come on quicker; scenes may require quick on. That same idea can be used for c/o's; the exciter supply may have to be adjusted a little higher to supply both the operating proj bulb and the 10% "not running" bulb.

As Jeff has indicated, this is well known in the broadcast and televison industries where over half a century of experience has proven that leaving equipment permanently powered on results in the least failures by a huge margin. Any small increase in the power bill is greatly offset by the reduced cost of repairs and replacements.

In one place I worked, they left the sound equipment on, and had very few problems. But I've worked in places that didn't, and also had vew problems.

Dust can be a consideration, however in a clean air-conditioned work environment, dust build-up should be minimal. Also many of the popular modern amplifiers have fans that only come on the when the internal temperature reaches a certain level, so they should not come on at all at night when there is no audio.

Obviously the decision to leave your sound gear on depends on your operating hours and many other factors. For example if you only show one session a day the increase in your power bill would probably outweigh any benefit. However for a cinema complex that runs from 10am until midnight, it may well be worth considering.

And no Ken, I was not suggesting leaving the exciter on all night - lamps are a different kettle of fish. Mark's suggestion of running it at 10% of normal when it is not in use, is a good one, but turn it off when you go home.

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

Our sound racks will stay on for the whole evening no matter how many performances probably becase the non-sync system is on the same breaker.

Mark brings up a good point about the inside of the glass envelope being deposited with tungsten. But the main issue is filament sag. Whenever I do a Dolbly checkup on our sound opticals the first thing I check for is filament sag which can alter the output considerably. I would think that this sag would be proportional to the amount of total time that the lamp is operated.

I have nevr changed an eciter lamp because it was burned out. Only because it was dark, the adhesive base had let go throwing the lamp out of alignment or that the filament was sagging out of specs.

I doubt that mono equiped theaters would have to worry much.

How come the US military are still using exciter lamps? I though you guys were supposed to be at the leading edge of technology.

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Indeed when I worked in broadcast television back in the late 70's we never did shut stuff down except to either work on it or move it. The only thing that was ever turned off were the beam switches for the studio cameras when they were not being used. Once a week we pulled maintainance on the TTU-100 transmitter and of course it was shut down for that for 6 hours every Sunday night. I never quite got used to having 18kv at 16 amps capacity flowing around me. That is the best job to hold to learn great respect for high voltage!
Mark @ GTS