Hi,
I didn't think fluorescent tubes (either T5 or T8) were considered green enough to be offered any tax concessions, but grants may have different criteria, and I know nothing about the grant side of things.
The article on page 22 of the March 2011 issue of Sign Update talks about
GDI and the tax concessions available with LED's
.
I think the GDI article is talking about something different as it is talking about allowing it as a 100% tax deductable expense, as opposed to a grant.
I know T5's are considered more efficient, but I believe it is very marginal. LED's are the most efficient by quite a way.
I have used T5's, there should be no problems with this. The fittings will be different to the T8's and the standard lengths they come in are marginally different, but I don't see any issues that would arise that wouldn't arise with T8s.