Okay I have a rather odd question and am not sure whether its something to be concerned with or not.
For a couple years now I've been using a bank of (8) 48" 40Watt T12 Flourescent Black Light Blue bulbs in a homemade UV box for my alt process printing.
Last night I had two bulbs go out on me. I found a place locally that sells them, so I bought some replacements.
The question I have is that apparently BLB bulbs come mostly in the T10 diameter as opposed to the T12 diameter.
They are still 40watt bulbs and BLB, but I'm wondering if the UV output will differ greatly if I replace the two burned out bulbs with 2 of the T10 bulbs.
Basically having a bank of 8 bulbs where 6 are T12 and 2 are T10. My thought is to put the T10 bulbs on the outside edges of the full 8 bank of bulbs.
Apparently most manufacturers are going to the T10 diameter because its more efficient and they still work in the same ballasts/fixtures as T12 bulbs.

May not be a big deal and the smaller T10 diameter might just make it easier to put the bulbs in