Why are metal halides more intense that flourecent lighting? Halides have much more Photosynthetically active radiation (PAR) and intensity than flourecent lighting does. Lighting is measures in ways greater than watts. So, as an example, lets say you have 300wts of Power compacts on a 100 gallon tank, and 300wts of metal halides on another tank. The halides have much more intensity and photosynthetically active radiation than the Power compacts do. This is why 300wts of Power compacts doesn't compare to 300wts of halides.
Watt for watt, halides emit the same amount of heat as flourecent lighting does. As dburr stated, the only source of lighting from the halides come from a very small surface area. Since the heat is consentrated into such a small area, it releases more heat around that area. Unlike halides, the flourecent lighting source and heat is released through the whole bulb rather than in a small area.
Watt for watt, halides have the same evaporation rate as flourecent lighting. Watt for watt, they also cost the same to run.
Halides, in my opinion, are much more efficiant than Power compacts, VHO's, and even T-5 lighting. Halides only need to be replaced every 12-14 months (with the exception of a few 20,000k Bulbs that are overdrived by a PFO HQI ballast).
I have 2x 400wt 10,000k Ushio's (on PFO HQI), along with 2x 65wt Actinic Power compacts over my 80 gallon tank. Do I run a chiller? No. I have two simple 4" Icecap fans and an "open back" canopy. I've never had any heat problems, so far, while running the halides. The temperature usually stays around 83-85 degrees F.
Take Care,
Graham
