Constant Voltage Control

During live production small variations in voltage that cause variations in light output and color temperature are not noticed unless extreme. In animation a voltage change between exposures or overnight can be very noticeable and a problem especially when shooting film as a final product. Some corrections can be made in post, but should be avoided. Here are several solutions.

1. Make sure that there are no large motors or other current hungry devices on the same circuits as your lights. Motors use a lot of power especially when starting up. If you have no choice you can have the set builders warn the animators when they are going to start a saw or tool. Many animators listen to music or whatever with earphones and won't hear warnings. Air compressors that turn on automatically at random are a problem,

2. For long projects you might get the power company to put in a separate larger feed and / or transformer just for your stages. You will then not be dependent upon non-lighting load changes on your transformer, but you will still be effected by voltage changes on the neighborhood grid. Industrial areas are the worst for voltages changes.

3. There are constant voltage transformers that will provide a constant voltage out and accept different voltages in. They do not react instantly, but take part of a second to recover from a drastic load change. These units are expensive, but can be sometimes found used. They are not UPS devices commonly used for computers today. (C-H Sales in Pasadena might have some surplus.

4. If you seem to have PM to AM changes and not much during short time periods, you might consider voltmeters and Variacs to maintain a constant voltage. Read the voltage often. You should see brightness differences in the Lunch Box over short periods of time. You will need Variacs large enough for all of your lights. (They are not cheap either.) We used a cheap digital VOM's to monitor line voltage.

5. Use large cables wherever possible. #12 wire extensions are good and 6' air conditioner extension cords are usually #12 and convenient. We cut some 25-foot extensions into 10 and 15 foot cords to reduce cable snarls.

6. If you separate individual set circuits from each other, it will allow changes in light load on a set being lit but not effect the other sets that are shooting.

It is wise to find out which wall circuits are on which circuit breakers with walkie-talkies. If ground fault interrupter sockets are used, find out which outlet resets the other outlets when a ground fault problem happens. Some ground fault testers have a shorting / test feature.

Note: Noticeable color and brightness changes in video images seen in the Lunch Box video monitor over long times can be drift in the video camera or monitor and may not be a voltage shift. The cameras usually stay constant over short times. I don't think that there is drift in the Lunch Box itself. Monitors and TV's can drift too, but we didn't seem to have that problem.

When hooking up distribution boxes etc. use heavy wire. Use fuses or breakers at your plugging boxes and GROUND everything possible for safety.

Harry Box's "Set Lighting Technician's Handbook" (Focal Press) is a gold mine of information about safety, lighting and studio procedures.

© Copyright 2004 Ron Dexter. All Rights Reserved.