This is kinda confusing for me. An inefficient light could consume 100 watts but produce so many lumens. That being said, couldn't a highly efficent light produce more light with less energy?
Yes. You have it correct. The more efficient a light source is, the more lumens it will produce per watt. A less efficient light source would produce less lumens, and more heat. The wattage used is the same, so if one source produces less light, the remaining energy is converted into heat. Energy must go somewhere.
Yes, you are on to the truth. You actually are not confused, but are being confused by everyone else who is confused... All that matters is how much light, and in which spectra, your plant gets. Wattage is simply a measure of consumption of electricity. It is people who do not understand this who are confused. The reason you hear so much about wattage is that it is easy to know about a bulb, in fact it's the biggest and most common piece of information on the package. And, with certain types of bulbs, we growers have come to know that a certain wattage of that kind of bulb gives enough or not enough light. So, "wattage" has come to be a proxy for the amount of light, but it really isn't a measure of light at all. For example, HIDs are about twice as efficient at converting watts to lumens as CFLs are. If you really want to make your head spin, realize that even lumens isn't a good measure of the amount of usable light for plants, but rather is way of rating the bulb, and only for spectra that are visible to the human eye. But at least it is some kind of measure of light output, whereas watts really has nothing at all to do with light, as you have figured out.
My, that was quite a response! Bravoo I "get it" pretty much completely now, thanks to you and stickies..Thanks!