I'm going to build my own cold light head for an 11x14 stat camera that I've converted to an enlarger, but I can't figure out the color temp necessary for optimum results. The other posted questions refer to "blue tubes" and "green tubes"...I'm looking for more specific info like Kelvin rating, etc.

Anybody able to help? Thanks in advance!

-- Bill Youmans (bill@greatgrips.com), March 15, 2000

Answers

Bill, You will not be able to get a true color temperature reading for any light source that is not a continuous black body spectrum, i.e. flourescent tubes, which emit only broken "bands" of light. If you are planning to use graded B&W papers, there should not be much of a problem. These papers are sensitive to "blue" light (check the specs for the exact spectral response), so tubes with higher output in the blue will be more efficient. If you are planning on using VC papers you will need to make sure that your tubes have enough output in both the blue and green areas (the two colors the two emulsions on the VC paper are sensitive to, again check paper specs) to make your filtration work evenly. Even if things are a bit unbalanced you should be able to work with filtration/exposure times and find a way to make VC work. The manufacturers of the tubes you are considering should have some info on spectral output of their products. Hope this helps. ;^D)

-- Doremus Scudder (ScudderLandreth@compuserve.com), March 16, 2000.

You can't strictly give fluorescent tubes a colour-temperature. They don't have a continuous spectrum, so they can't be directly related to a black-body radiator. Also, a lot of the actinic light from these tubes is in the near UV, and so their brightness to photographic paper is a lot more than any visible colour temperature would suggest. You really need to get hold of the manufacturers spectral distribution graphs for any tube you're considering using, and compare the output in the green/blue/UV region.

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 16, 2000.

Ha! You beat me to it this time Doremus. I've really got to stop posting the same responses, at the exact same time as other people.

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 16, 2000.