So I'm like spellcheck for planted tanks now?
A watt is a unit of energy consumption. In an ideal world, there would be a 100% conversion of electrical energy consumed to light energy produced, but that world doesn't exist yet. To explain that, lets look at an incandescent bulb: 40w, some light, lots of heat. In this case, much of the wattage used by the bulb is converted to heat energy rather than light energy, which is unfortunate. Now another example, a CFL bulb: 10w, more light, less heat. It's a much more efficient. The T12-T8-T5 paradigm roughly follows this as well, with newer technology being more efficient than its predecessors. This is also one of the major dooming factors in the watts/gallon rule, as it came about in the T8 days, and T5HO are a really dramatic improvement. LEDs continue this trend, with many of them working cooler and more efficient than old fluorescent bulbs.
Now, in this case, we're comparing watts to watts, to the comparison should be much more literal. 50 watts are being used, 32 watts are accounted for with the bulbs, so where is the remaining 18ish watts being used? Maybe some of it is lost in heat, but it seems very wasteful by LED standard. Possibly some inner computer works that need power? I don't know what's causing it, but I'm inclined to believe its a math error somewhere by someone, hopefully not a deliberate oversight.
