The usable life of VHO's is actually about 18 months if used with electronic ballasts. I prefer 3 Super Actinic URI brand VHO and one Actinic-White URI brand VHO used in combination with two 15000 Kelvin MH lights.
T-5's as used today are more effecient using less power per lumen of light produced, but do not deliver as many lumens as a VHO tube. Unfortunately, most of the T-5's I've seen in service fail to light within a year.
Wattage is a term which actually tells how much electricity is used. Lumens is the amount/intensity of light coming from the bulb/tube. Unfortunately, lumens is not a good measure of PAR (Photosynthetically Active Radiation), the measure of how much good coral light is being produced.
Actinic bulbs/tubes produce bluish light at a wavelength (420 nm) that most coral seem to need. SPS coral is the exception, because most varieties of SPS live in shallower water where a wider range of the light spectrum is available. Though whiite light has this 420 nm wavelength, Actinic tubes produce only this color so electricity/energy isn't wasted producing a wavelength of color which is not as beneficial to coral.
I invite you to examine these pics of the lighting that reaches the ocean and with an understanding that, with the exception of Acropora and related SPS coral, much of the coral we keep comes from depths of 10-50 feet, decide for yourself if actinic light is necessary or not. (photos courtesy of Jacque Cousteau)
Edited by Mark Peterson - January 07 2007 at 5:58pm