I just found this out recently myself. Whatever the number is (12, 5, etc) divide by 8 and that is the diameter of the tube. For example, a T12 is 12/8, or an inch and a half in diameter.agreed. im not sure what the difference is between T5s/T12s/T8s etc.
are those considered the HO? and good to kno. im just curious, heres my grow>>> https://www.rollitup.org/indoor-growing/373324-first-grow-more-then-i-post4732532.html#post4732532o rit could be t-12=really old t-8=alittle newer t-5 late 90's tech, t-4 is the newest bestest.
good point.I'm surprised so many people are opposed to fluoros for seedlings and early veg. Especially if you already have few of them on hand. Throw a few 6500K daylight tubes in and your good to go for the first 2-3 weeks. Also good if grow space is limited and you want to have a separate room or cab for vegging while your flowering room is occupied. They don't create much heat so no need for any elaborate ventilation. Even in the summer a single oscillating fan was enough to keep my cab cool enough. Just have to keep them really close. I've vegged (2-3 weeks) with both fluoros and 6500K CFLs and didn't notice any significant difference. Except of course the added heat to deal with when using the CFLs. Never used MH so can't really comment on that, but fluoroscents will work for veg.
As for flowering, I don't think it is recommended. In that case I would definitely choose CFLs over fluoros if money and/or room were issues.