Hi, I've been following this thread for a bit and happened upon this:

LEDs used to produced plant antioxidants - UPI.com

Hope this isn't too off topic - I wasn't sure where to post. In any case, you can just check google news for "UVB led lettuce" and you'll see there are a few different news outlets showing interest.

I asked for a quote on Seoul's Optodevice 280nm LEDs a while back and all I can remember of the experience now is the sound of my jaw hitting the floor. I think that reptile lights offer a more affordable alternative - that is, if they work as well as the aforementioned LEDs. I'm not aware of any other UVB sources. Even incandescent bulbs appear to produce minimal UVB according to these sources:

No UVB from tungsten filament incandescent lamps

http://www.flukerfarms.com/PDFs/Lightbulb-FAQs.pdf

I recognize that we're not trying to grow lettuce here (it's tomatoes, right?). Regardless, the theory that resin is, in part, a defense against solar UVB radiation lends plausibility to the supposed benefits of UVB.

Thanks to everybody who has been posting. I'll be sure to contribute more once I've started work on my own LED arrays.