Kyuss
Megistered Rember
It may be possible, but it's very likely to either under-drive or over-drive the bulbs by quite a bit (in this case I'd wager over-drive, which could end really bad.) Even if it's manageable and works, if the manufacturer doesn't list that bulb type for a particular ballast and something were to happen, fault is going to fall squarely on you - any insurance will be quick to point the finger too - and that's a really big risk to take IMO.
I use 80W bulbs so I'm not as familiar with the smaller sized lamps, but I think 18W t5's are sort of a "wildcat" size and so not much for options for DIYing, but I could be wrong. The spec sheet for the ICN-2S24 doesn't list anything for 18W t5, and I don't know if you'll get more than a simple "No." from them if you email them about it.
I use 80W bulbs so I'm not as familiar with the smaller sized lamps, but I think 18W t5's are sort of a "wildcat" size and so not much for options for DIYing, but I could be wrong. The spec sheet for the ICN-2S24 doesn't list anything for 18W t5, and I don't know if you'll get more than a simple "No." from them if you email them about it.