Fluorescent light fixtures in general produce more light for equivalent amounts of energy when matched against incandescent lights. The same goes for compact fluorescent bulbs (abbreviated to CFL). Tracking the energy used is the same for all lights: You use the wattage. Once you know the wattage of the lamps in the fixture, you can determine the energy use by tracking how much it is used. In the end, you get a figure in a unit known as kilowatt-hours. This is your electrical billing unit, and the way your electricity consumption is measured.
Check the wattage of all of the lamps or bulbs in the fixture in question. If it is a single-bulb fixture, as a CFL or a single tube, use its wattage; for a double tube or more, add the wattages of all the tubes.
Track the duration of use of the fixture. Log it in hours. If you are tracking for economical reasons -- you want to see what it costs to use -- a monthly tracking is logical. You can estimate if you don't have the exact hour figure.
Multiply the fixture's wattage by its hours of use. For instance, a double-tube fixture with a total wattage of 80 watts (two 40-watt tubes) in operation for 240 hours per month uses 19,200 watt-hours of energy.
Divide the watt-hours by 1,000. Doing so reveals the energy use in kilowatt-hours. Here, the result is 19.2 kilowatt-hours. If your utility charges, for example, 12.5 cents per kilowatt-hour, then the cost of the fixture is $2.40 per month.