There's no calculation, only an estimate. And it will be different for every tube and ballast. Expect around double the output, but might be only 1.5 times or might be nearly three times. You can overdrive as high as you like, bulb lifetime will decrease, electricity consumption will increase, and fire hazard will increase the higher you go. Eventually, the tube will blow almost instantly, the ballast may fail to start, or the ballast may be damaged (unlikely). Remember, overdriving isn't magic and it isn't something for nothing. It is a means of producing higher light intensity from standard fluorescent equipment and the price is your utility bill goes through the roof. There are other means of producing high light intensities that are more efficient and safer, check them out before you decide to overdrive.

I can't answer your question myself, but the link has a matrix showing compatible ballasts for some T5 tubes. I would certainly avoide the commercial offerings, way overpriced.

Once again, thanks, jon. In checking out other threads on this forum, I see you've also aided others in their 'lighting dilemmas', along w/other very knowledgeable folks in this area. Nothing like a forum to learn the REAL facts! When I put my changes to the fellow last night, he balked and couldn't understand why I'd need more light. Uh, he's, like, about 30 years younger than I am, and my eyes aren't what they used to be - which wasn't good in the first place. Still, I couldn't convince him of this, nor should I have had to. This wasn't the first time we'd gone round on this. Hard enough to live w/bad eyesight, but harder still to have to justify any enhanced visual needs to someone. While I'd gladly leave the tech stuff to him, I figure I'm a better judge at what I can and can't see and the degree of difficulty given particular lighting parameters. Not to mention, it IS my money after all! Ultimately, armed w/info I received here and my reluctance to proceed w/him further on this particular issue, I opted to have him just do all the other electrical work I needed done in my house (we're remodeling) and skip the undercabinets....for now. Besides, after my cabinets & countertops are installed I'll think I'll be better able to judge exactly what I need/want once I've had a chance to 'live' w/the new lighter cabinets,countertops and overall lighter colors in my kitchen, which may affect my choices, too. Maybe even go fluorescent! Who knows? Depending on how things proceed w/him from here re the rest of the work he'll be doing, I may have him back to do the undercabinets later....or call someone else who I feel I can work better with and who'll be more understanding and cooperative re my specific physical needs. Thanks, again, to you for helping me become a much more educated consumer. :)

You've got the first two right -- halogen incandescents are a bit (sometimes quite a bit) more efficient than standard incandescents. Fluorescents, including CFLs, are a big step forward. I haven't read extensively on LEDs, but what I have read suggests that, at this point at least, they are generally less efficient than fluorescents. Their strengths seem to lie elsewhere. Part of the problem there is that many LEDs are offered with little or no photometric data, marketed on the basis of their gee-whiz factor alone... that's my impression, anyhow. Beyond the ones you listed are high-intensity discharge lamps, but lousy color rendering seems to go with their greater efficiency.