On some of these attributes that are being described (and BTW there are a number of archived threads on the subject):
CRI:
Color Rendering Index (CRI) trumps all in my personal opinion, and most people that muck about with color
temperature are usually using it as a proxy for CRI. This subject requires popcorn, but loosely it's important if you are painting, convenient if not. See
http://en.wikipedia.org/wiki/Color_rendering_index for gory details. At least no one has recommended "full spectrum" lamps, which would drain an entire bar in order to discuss.
Length:
In general, 4ft is used inside (offices, libraries), 8 ft is used in warehouses and factories. 8 ft fixtures can be really loud!
Ballast:
Electronic is best, magnetic ones are being phased out. What you want to compare is efficiency.
High Output:
Designated as "/HO " on the tubes, these are more light per lineal foot. Of course just like RVs there is a tradeoff. Usually it's noise and efficiency. Efficiency is
sometimes better in HO than regular, but never as good if you go all the way up to VHO. (Hint: hang any fixture from chains in order to avoid turning the ceiling into a sounding board that amplifies the noise.)
Bulb Diameter:
The number is diameter in eights of an inch, so "T8" is 1" diameter. T8s are more efficient than T12s. As others said, T12 is being phase out.
So my bottom line "cut to the chase" recommendation is:
- Use 4 ft T8 Cool White fixtures with electronic ballasts, hung from chains, in your garage if it's heated and less than 12 ft ceilings
- Use 8 ft if heated and high ceilings (saves some $$)
- Use HO if temps will be below 50F all the time, or below 20 when you first turn them on.