I was just wondering if I misread something because I was always told that humidity was bad for the booth and all of the theatres i worked at except for 1 had DEhumidifiers in them that we had to empty every morning.

You want the humidity in your booth to stay in the range of 50-60%. If the levels get too low you'll need to humidify. If the levels get too high then you'll need to DEhumidify.

Emptying out the DEhumidifiers? That's just as much a pain in the arse as filling the humidifiers... just in reverse. Do you have a way to hook a water hose to the thing and just run the condensate down the drain? Most dehumidifiers have this option.

I will be comming up to Kentucky next week. Actually I'll be going to Louisville but I gotta' come through Lexington. I'm due in Tuesday.

At very high humidity, the gelatin emulsion becomes softer, such that it may scratch more easily or build up as hard deposits on the hot projector gate. Damp conditions may actually make the film sticky, and even CAUSE a static problem as the sticky film pulls apart during unwinding.

If the humidity is much higher than 60 percent, use a dehumidifier, which removes moisture from the air by condensing it on a refrigerated coil. Most air conditioning systems also remove moisture from the air. Excessive moisture is usually only a problem in the summer, during rainy or very humid weather (e.g., Houston, Miami, or New Orleans in the summer, or the Pacific Northwest almost anytime).

If the relative humidity is too low, use an evaporative humidifier to add moisture to the air. These humidifiers blow air through a wet foam pad or fiber filter material, and often can humidify over 10,000 cubic feet of space. Do NOT use an ultrasonic or misting vaporizer --- they actually spray water droplets into the air, leaving behind deposits of the salts and minerals that were in the water (not good for electronic components or film cleanliness). Steam vaporizers that actually boil the water usually don't have much capacity, and use alot of electricity.

Always monitor your humidity with an accurate digital humidity gauge or a sling psychometer. Radio Shack, Edmund Scientific, etc. sell these. The cheap analog dial gauges are often inaccurate and difficult to calibrate. Humidity can also be estimated by observing how a short piece of print film hangs --- it should be fairly flat, with just a bit of positive curl. Excessive positive curl indicates excessively dry conditions. Negative curl shows too much moisture. Again, the goal is to maintain between 50 and 60 percent RH.

You will find that the humidity will vary with the outside weather, and during the day. Large amounts of air are used by the lamphouses for cooling, and their heat dries out the booth. If possible, cooling air for the lamps should be supplied from an outside source, so the humidified air in the booth doesn't go up the vent. Venting the lamps into the projection room is a BAD idea --- the room will quickly become too hot and dry, and the ozone generated by xenon lamps is not good for your health. Most construction codes require venting the lamps to the outside.

Fortunately, the 50-60 percent humidity that is best for film, is also the most comfortable for people.

Here is some published information from Kodak:
http://www.kodak.com/country/US/en/motion/programs/student/handbook/physical4.shtml
http://www.kodak.com/country/US/en/motion/newsletters/reel/september99/pointers.shtml
http://www.kodak.com/country/US/en/motion/support/h1/base.shtml
http://www.kodak.com/country/US/en/motion/support/h1/base.shtml#other

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion