From IceCap:
A few fact checks.
MH bulbs on an electronic ballast don't need to be replaced in less than 18 months for a reef application. The height, reflector and bulb used can all effect the light you get for a given amount of electricity. High frequency electronic ballasts run MH with a constant arc. 60Hz conventional ballasts literally strike an arc 60 times a second, every second, on/off .... Which would you want?
T-5 HO lamps, run on a T-5 HO ballast or overdriven by an IC VHO ballast last around 24 months if a fan is run while they're lit. (The WH is not a T-5 HO ballast.)
If wattage, even output wattage is what you measure than you are not going to get the most PAR per watt. PC lamps are usually not efficient over a reef tank do to their design. T-5 HO lamps of half the PC wattage can out-perform PCs if single lamp reflectors are used. The same magic doesn't work with a PC.
The most efficient lamp is a T-8, yet even industrial applications of MH are switching to T-5 HO lamps because the light levels where you need light are higher with less wattage consumed.
Andy