t8 bulb spacing for uv light box

[macclad]

hi guys

i have followed the instructions from edwards engineering in order to buold my light box:

http://web.archive.org/web/20010127065200/http://www.eepjon.com/Ubldit.htm

i have just purchased the bulbs and the only cheap bulbs i could find in the uk are t8 bulbs, these bulbs are 1" in diameter as opposed to the t12 bulbs that edwards engineering suggests which are 1.5" in diameter. how should i space these bulbs now? am i going to have to modify my box so it is higher away from the print in order to avoid lighter and darker patches or should i space my bulbs closer together and just lose some of the maximum print size capability of my box.

does anyone have any experience of working with t8 bulbs?

any help at all would be great

 

[mjs]

Just as a point to remember, the maintenance guys here at work have been replacing the ballasts and stuff in all of the overhead fluorescent lights over the past week. I asked why and one of them told me that the T12 bulbs are obsolete after next year and replacements will be difficult to get, so they're converting all the fixtures for T8 bulbs.

Mike

 

[R Shaffer]

I used the T8 bulbs ( 18" long ) in my DIY UV exposure box. I have 8 bulbs spaced @ 1 5/8" centers. I started with the bulbs about 5" above my contact frame and I have it down to about 2" now. I don't see any variation in exposure in my regular printing. It covers 11 x 14 nicely. The output of my ( cheap ) BLB bulbs have significantly dropped since new. They seem to have stabilized now, but it was a real pain for a while.

 

[macclad]

yeah i heard that too so it was another reason why i ended up choosing the t8 bulbs. i just cannot find any info on the spacing of the bulbs in relation the height from the print.

 

[Dan Dozer]

I use 18" long T8's and spaced them as close together as I could get them and still get my fingers in between to be able to change them when needed. That means at most 1/2" of finger space between each one. I also have them pretty close to the paper (2" or so) and have never had any problem with scalloping of the tones (light and dark strips) at all. My box has 10 tubes that are 18" long for my standard 11 x 14 print frame. I probably could have used a couple less and still had enought light area for the contact frame.

 

[macclad]

hey guys

i have pretty much finished the box now. I ended up spacing them 1.3/4" apart. I'm thinking if it isnt close enough together i will just build some small legs onto the side of the uv box and make it a few inches higher from the negative.

many thanks for all the advice