From: Sandy King (sanking@clemson.edu)
Date: 10/26/01-04:01:56 PM Z
As you may know from a previous post I am preparing material for an
article on actinic light sources. In preparing data for the article
I ran a series of tests today with four different exposing lights in
both Van Dyke and Carbon. The lights were:
1. URI Super Actinic 24" VHO (75 watts)
2. 24" Sylvania 350BL (Black Light), 20 watts
3. 24" GE BLB (Black Light Blue), 20 watts
4. Metal Halide Lamp, 1000 watts.
The exposing negative was a Stouffer TP 45 step wedge. All tests of
same process were on paper sensitized and developed together. I
repeated all tests twice to verify results.
The three tests with the fluorescent tubes were all for 10 minutes,
with the printing frame at exactly 4" from the front of the tubes.
All of the tubes were allowed to warm up for five minutes before
beginning the exposure.
The test with the metal halide lamp was done with an integrator set
for 150 units, or the equivalent of 2.5 minutes, with the printing
frame at 20" from the light.
In the article I am preparing on this subject I plan to provide
curves and complete data for all of the tests. However, you may be
interested in some preliminary observations.
1. There was a huge difference in visible light between the Super
Actinic, BL and BLB tubes. The Super Actinics put out a very bright,
bluish/violet visible light, the BLs a bluish light, less intense
than the SA, and the BLBs a very pale blue light.
2. In a comparative sense carbon is about one full stop faster than
Van Dyke. However, both carbon and Van Dyke exhibited similar
response to the different lights, both in terms of speed and contrast.
3. No surprise but that the metal halide unit was much faster (more
than two full stops) than the other lights. It also produced greater
contrast.
4. No surprise that the 75 watt Super Actinic was much faster (by
over a full stop) than the 20 watt BL tubes. It also produced greater
contrast than the BL tubes.
5. The *Big* surprise for me was that the GE BLB tubes were also much
faster than the BL tubes (and of about the same contrast). In fact,
the 20 watt BLB tubes were even faster (by about 1/2 stop) than the
75 watt Super Actinic tubes!!! I was really quite surprised by this
result because for as long as I can recall the urban myth has been
that BL tubes are quite a bit faster than BLBs. Which makes me wonder
if anyone else has ever actually made an apples to apple test
comparing the BL and BLB tubes? Or if folks have just been passing on
erroneous information?
Sandy King
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