In article ,
"Brian Gaff" writes:
So why might that be the case them?
I'd have thought there would in fact be little difference unless the actual
phosphor is different.

I think most T8 tubes nowdays are compact fluorescents, meaning
they contain an amalgam pellet to regulate the mercury vapour
pressure inside the tube. I doubt they can get the mercury dosing
low enough otherwise. The tube and the amalgam pellet have to warm
up to liberate the right amount of mercury for the tube to operate
at the correct mercury vapour pressure. Also, it can take some minutes
for the mercury vapour to diffuse along the full length of the tube -
before that, the middle of the tube may be noticably dim as the gas fill
which starts the discharge doesn't give off UV to excite the phosphor.
This latter effect is very noticable when the tube hasn't been used
for a long time.

The phosphor in T8 tubes is a tri-phosphor or poly-phosphor coating.
The phosphor in T12 tubes is a halophosphate traditionally, although
some of the last T12 tubes had switched to use tri-phosphor coatings,
but that made them expensive as they need twice as much as a T8, and
it's more expensive than halophosphate coatings anyway. However, this
is not related to run-up times.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]