Quote Originally Posted by jamstigator
They use more power (compared to a 400-watt HID light), and generate less light, so that reduced efficiency and extra power usage is being turned into *something*. If it's not light, and it's not matter, then what else could it be but heat?
Do not get confused mate here. Do not compare the efficiency of 2 different systems by subtracting their wattage difference to heat. Other reactions needs to be done in actual-physical level on each lamp type. The energy is used in totally different principles, so any attempt to compare is by definition wrong. Not only light, heat and matter can be present on the equation, as you say.
Fluoro-atoms release light photons when their electrons become excited. In High Intensity Discharge lamps, light is produced by passing a current through a metal vapor. So we talk about different mechanisms here, with different & uncomperable efficiencies.

-HPS produces more heat, more lumens and dirty light.
-T5HO produces less heat, less lumens (yet) and quality light.