Re: best light for light box

[Sandy King <sanking@clemson.edu>]

Judy Seigel wrote:

>
>Some folks find "regular" fluorescent bulbs good for carbon printing (I
>think it was the "bright white" type), but not for other processes.
>They're probably the cheapest, but since the BL are rated for 7000 to 9000
>hours, and exposures are one to 10 minutes, that's probably irrelevant.
>

The "regular" fluorescent bulb that I found worked ok for carbon 
printing was the GE "Daylight" tube. I did some comparison tests with 
this bulb and my regular Sylvania BL tubes with carbon printing some 
years ago and reported the results to the list. What I found was that 
the Daylight bulbs produced more contrast and less sensitivity than 
the BL bulbs with a dichromate sensitizer of a given strength, but 
that by adjusting the strength of the sensitizer it was possible to 
get results that were virtually identical with the two lights. I was 
initially quite surprised by these results  but later found out that 
the Daylight bulbs have a big spike of radiation at about 520 
nanometers, and it turns out that carbon (and perhaps other 
bichromated colloid systems) are quite sensitive to light at this 
wavelength, even though they are most sensitive in the 350-450 
nanometer range.

I eventually switched back to the BL tubes, primarily because of a 
data base of printing with them that goes back over 15 years. My 
personal opinion is that the best "all around" light for working 
different alternative processes such as cyanotype, gum, salted paper, 
kallitype and carbon, is the 350 nanometer BL tube, and I agree with 
Judy that there is not much difference among brands. In fact, two 
brands (GE and Sylvania) are mixed in my own light box about 50/50.

Sandy King




>Judy
>
>.................................................................
>| Judy Seigel, Editor                           >
>| World Journal of Post-Factory Photography     > "HOW-TO and WHY"
>| info@post-factory.org                         >
>| <http://rmp.opusis.com/postfactory/postfactory.html>
>.................................................................