Yes, I grow commercially, so I apologize if I've taken this question far beyond what was relevant. I debated responding at all, but thought I'd put in my own setup as another example. I think Ken did a great job explaining light usage, though I might quibble with the blue/red generalities.
PAR is Photosynthetically Active Radiation and refers to the light which actually can be used by the plant. This is different than Visible Light, which is viewed by your eyes and usually the only thing indicated by the lumen ratings on light bulbs. It is also different than total output from a light source, which often includes ultraviolet and infrared. Much of the lighting industry rates efficiency in terms of the amount of visible light (lumens) produced from a source per (electrical) energy used. What we care about for growing plants is the amount of PAR produced per energy used.
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This is complicated and more information than needed in a small setup, so feel free to stop reading now, but I'll try to explain what I was talking about earlier for the curious:
The PAR curve doesn't directly match the chlorophyll absorption spectra because of secondary light gathering pigments such as carotenoids, and the fact that lower wavelengths carry more energy but don't necessarily contribute more energy to the plant. However, the important thing in the light source is to make sure that the emission spectra (usually available from the manufacturer) fall within the large parts of a standard PAR curve (easily found with a google image search). Fluorescent bulbs in particular tend to only radiate in very narrow bands around their constituent phosphor emissions, and if these bands aren't on your PAR curve, or are in parts of the curve that are only weakly utilized, they're just wasted energy.
Individual plants, based on their photosynthesis profiles and the pigments they produce, have different PAR curves, and these can vary with maturity, season, and life cycle. Most of the time, though, you can get away with matching to a generic curve, and most daylight rated bulbs have emissions spectra within the PAR curve. Most of the time it doesn't matter. But these gross estimations are part of the reason why it often doesn't pay to mix warm and cold bulbs or worry overmuch about the light fixture, unless you really plan to do the research and adjustment to properly take advantage of them. You'll need spectra sensitive light meters to do more than stab in the dark (metaphorically) toward the results you're looking for. Even then, savings can be slim and results difficult to measure. If, on the other hand, you're starting tens of thousands of plants, then power savings, growth consistency, internode management, and lifecycle triggering all make it worthwhile to really pay attention to your light.
