In many ways a florescent bulb is actually far less efficient than a pressurized gas lamp. This is difficult to explain and doesn't mean we shouldn't all use florescent bulbs for tons of uses for which they are more energy efficient. When a Photometrist measures the ratio between the total luminous flux emitted by a device and the total amount of input power (called the LES, or "Luminous Efficacy of a Source" that's: efficacy, NOT efficiency) they find that florescent lights create somewhere along the lines of 46-72 lumens/watt while a high pressure sodium bulb will produce 85-150 lumens/watt. This translates into an luminous efficiency (NOT efficacy) of 8-11% for the fluorescent and 12-22% for a pressurized sodium bulb. This is not a luminosity-in-one-spot measurement, it's based on the ratios determined from how that light reading changes through space and reflection.

It is hard to explain how this applies to the CFL versus HPS decision for a grower, but it has a lot to do with the penetration power of the light, as well as the power of direct vs. reflected light from the source. As long as you have a thinner canopy with fewer buried/shaded leaves, you're going to get more result with less power usage with LEDs or CFLs. As soon as you are trying to penetrate a dense canopy or throw the light a long distance from its source, you're going to need something like a gas bulb to see results from increased power usage.

Your grow looks to be at about the limit of where a florescent lit space will be more power-efficient than a similarly producing (grams/watt/cubic-foot) grow using gas bulbs. If you ever decide to pump a bunch more power into the space in hopes of getting more yield, you should do it in the form of a pressurized gas lamp or two instead of more CFLs. As for now, I see nothing but sweet sweet lung candy.

Keep up the good work! :rasta: