some key points to remember when comparing these things are
1) The long term real world cost of operation of an item (electricity used, usable life span of components, more money spent on cooling {both on bigger fans, and more power to run them}, for instance)
2) comparing apples to apples, when researching (a 400 watt laser will probably cut you in half, but it will not help you grow a plant, i.e., comparing wattage alone is insufficient....does anyone have a definitive answer on exactly what spec to compare? Lumens? Lux? Lex Luthor? )
3) There are also some intangibles that are harder to calculate, but are still worth looking into like the noise a fan system makes when it has to pump a lot more air, which would be a security issue, and the fact that if a light has to be a certain distance from a plant in order not to roast it, you are effectively shrinking the usable height of your grow room. (I know that people have had success cutting that distance down by adding fans, so if that method is chosen, the calculation gets more complicated, because now you still have some height lost, but now more money is spent on fans, and electricity to run them)
A person can get even crazier trying to factor in everything. For instance, if you are in a cold climate or season, and you are venting the heat back into your house, the energy lost to produce and vent the heat is offset somewhat by the fact that the heat is a usable by product for you, although it is heat that was produced by electricity, which is still the most expensive way to produce heat, even with current oil prices. Thats math that gets really complicated really quickly, though, so I am guessing its probably best to get the major stuff ironed out first, before delving into that part of it.
my $.02
