Okay, long story, converting some T5 lights to run on 12v. Got some 12v dc ballasts and they're rated at 21W.
Only problem is I can't find a 2ft 21w bulb. I can find a 24w t5 bulb but is it better to have a bulb rated higher than the ballast or vice versa. My understanding is that the ballast partially acts as a current limiting device so I would imagine a bulb rated higher than the ballast is okay. But is it? Websites talk about bad things if you mismatch them- is this still true with electronic ballasts or more with the old magnetic types?

thank in advance

I don't know much about it, but by chance I was reading another forum 10 minutes ago and read that electronic units typically run the tubes at high frequency (where they are 10% or so more efficient) and that the EU requires electronic units to under-run the tubes, so as to give the same light output, but reduce power consumption. I don't know how true this is, but if it is the case, your tubes would be could be run at around the right power anyway!

Looks like I'll give it a try and see if anything goes pop