Can someone please explain what T8, T12, etc. are and what are the
differences? I have plenty of old T12 40W tubes, fixtures, ballasts,
etc. I've had several people recommend updating the ballasts and tubes
but are the keystones the same? Length of tubes?

nate




T = Tubular

The number is the diameter in 8ths of inches. Another number in the full
designation is usually the nominal wattage, but sometimes the length in
inches.

Examples:
F40T12/CW Fluorescent, 40 Watts, 1.5" diameter, Cool White
halophosphate phosphor

F32T8/850 Fluorescent, 32 Watts, 1" diameter, 80+ CRI 5000K
trichromatic phosphor

F96T12/D/HO Fluorescent, 96" length, 1.5" diameter, Daylight
halophosphate phosphor, High Output (800mA)

and a really rare bird...
F48PG17/D Fluorescent, 48" length, 2-1/8" diameter Power Groove
dimpled tube, Daylight halophosphate phosphor, VHO (1500mA)



T8 and T12 use the same sockets and have the same lengths. High Output
(HO) and Very High Output (VHO) are also available, those use RDC rather
than bipin end caps and are slightly shorter to accommodate the larger
sockets. Fixture lengths are the same for all those.

Not all ballasts are created equally. The wattage stamped on the tube is
the nominal rating. The actual power is determined by the ballast, which
is a constant-current source. The low energy retrofit tubes such as the
34W T12 accomplish this by changing the gas fill to have a lower voltage
drop, so with the same current, the wattage is lower.