This page analyzes T-5 vs some other options:
http://www.advancedenergy.org/progre...5versusT8.html
(Note that the math is off on lumens per year per bulb cost in
Table 2. It lists a T-8 bulb at around a quarter of the cost of a
T-5 bulb, with a lumens output around 10% higher on the T-8,
yet shows a lower per lamp cost per year for the T-5. Lumens
per watt cost, at the top of the table, looks about right,
without getting out a calculator to check.)
It was interesting that T-5 optimum operating temperature
is much higher than for a T-8 or T-12. The T-5 HO bulbs seem
to be designed to replace metal halides in high bay lighting
(warehouses and similar).
(FAQ: the "T-digits" designation refers to eighths of an inch
in bulb diameter. T-12 is 12/8 inch diameter, or inch-and-a-half
diameter bulbs; T-8 is 8/8 inch, or a 1-inch diameter bulb;
T-5 is 5/8 inch, or a little more than 1/2-inch diameter bulb.)