Building a UV Exposure Unit: GE Black Light Blue F40 T12 ?

[cheekygeek]

Greetings all,
I've got a ReStore in my area that I check every Friday. Today, I found some NEW GE Black Light Blue F40 T12. I got 5 of them for 50 cents each. They are 48" long (which is longer than I would have planned to build a unit for, but for THAT cheap...

So my Googling tells me that they are UVA, which is what I want for Alternative Processes (right?). Since they go for about $18 ea on Amazon, I figured I would buy now and figure out things later. Would appreciate it if someone would confirm that these tubes are good for a UV light table for Alternative Processes.

I have some two-tube ceiling units (4 altogether) that will handle two F40s each. The spacing between the tubes in each of them is 5" apart. The distance from the center line of the tube to the edge of the fixture is also 2-1/2" so I should be able to mount them right beside each other and maintain a 5" center-to-center distance between the tubes. Right now (without buying a 6th tube) that gives me a (what?) 25" x 48" light coverage? Adding another tube should give me 30" x 48" light coverage?

I'm wondering how DEEP I should make the center of the light tubes in my DIY Exposure unit, given those dimensions for even coverage. Is there a calculation for that?

Thanks in advance!

 

[cheekygeek]

Pulled out some books and I see in "Jill Enfield's Guide to Photographic Alternative Processes" that she says (on page 19) "make sure you buy "BL" (black light) and not "BLB" (black light blue) bulbs. BL bulbs have enough ultraviolet light require relatively short exposures, whereas BLB bulbs emit less ultraviolet light and are also expensive."

Well, I can forget the expensive part. Will they still work, just require longer exposures? From this GE spec sheet I found, it looks like the BLB is more "pure" UV (filters out other nm) but is only about 55-60% of the output of regular blacklight bulbs (but it is the same nm).

 

[cheekygeek]

OK, answering SOME of my own questions (perhaps)?

According to this source, BLB bulbs are fine and will only require slightly more exposure times than BL. (They should still be less than is needed by variable sunlight).

Regarding spacing issues, I found this PDF on the issue (screenprinting uses similar exposure units and also wants to prevent banding issues).

Now I'm also wondering if using a reflective surface behind the bulbs (on the same surface that they are mounted to) would be helpful in providing even illumination and/or shortening exposure times. A solar reflective material (as use in windshield dashboard protectors or insulation, might be a relatively inexpensive way to do that.

 

[pschwart]

http://unblinkingeye.com/Articles/Light/light.html

- 5" spacing is way too far apart. You want the bulbs very close together for even coverage.
- BL bulbs work very well and are inexpensive. You saved a few bucks on your T12's, but I wouldn't use them.
I'd recommend T8's as they are more efficient. Use an electronic ballast (smaller, lighter, no hum).

 

[cheekygeek]

Thanks for the reply and input, Philip.

Since posting my question I found these pages, using the Wayback Machine:
https://web.archive.org/web/20030603155830/http://eepjon.com/Uv.htm
Plans with tube spacing: https://web.archive.org/web/20030603171857/http://www.eepjon.com/Ubldit.htm
UV FAQ: https://web.archive.org/web/20030603162557/http://eepjon.com/faquv.htm

I also went back to the ReStore and found a box of 24" ACTINIC BL F20T12/BL so bought the whole box of 19 for .50 ea. They would allow me to build a smaller unit, but I would have to buy all new ballasts, wire and socket ends. Still a no-brainer to snag them.