Joel A
Started over.
If you factor in the t-5's fans running 365 days a year as opposed to the few weeks fans are needed with a mh setup things get much closer. Then when you factor in the heater not coming on when the mh's are on 365 days a year, as opposed to the constant need for a heater about 8 months a year with t-5's, game over, mh wins. Also, certain mh bulbs hold their intensity much longer than t-5's, so the need to replace t-5's more often would negate any electricity savings. I say get what you like, the savings are negligible...
... i'm going to look up how much wattage the fans in my fixture use... probably not much.. and you should always have fans running in your Metal Halide fixtures as well, if they aren't it will decrease life span.
t5 bulbs are replaced 10-12 months, just like metal halides... sure you have people who are more worried about that and replace the t5 bulbs every 4 months, or 6 months, but it's not necessary.. so that point becomes moot IMO.
You do have a point with the heater not coming on during days with the metal halide, but IME it's more or less the same... if your house is heated, and your not running a basement sump... heaters don't really come on all that often.. mostly at night, and the metal halides aren't on at night...
In my experience, t5's will heat up a tank during the day similar to metal halides, just not quite as much... i'll come home during the winter to find my tank at 79-80 degrees (when the t5's are on) and the heater is set to 78, so it's obviously not working during that point..
AND, for every day that a metal halide set up might run you less electricity because it adds more heat, those days are more or less canceled out by the hot days in the summer in which you don't have to run your air condition/chiller/fans as long, or as low....
but i agree with the general theme, when it comes to energy efficiency lights are not what kill you, because they're going to be expensive energy wise no matter what... what kills you is high wattage pumps running 24/7... at the same time though, i do still believe t5's are more energy efficient... just not a HUGE difference.