Can anyone help me to compute how much energy a fixture with two florescent lamps and electronic ballast uses?

Question

The fixture I'm looking at is two F32T8's. So I think thats 32 watts.

Answer 1

Electronic ballasts cause harmonic distortion, which may alter the true power used.

Assuming the power consumption figure listed on each lamp (for example, 60 W) is accurate, you can estimate the energy consumption with a few numbers:

The meaning of a watt (W) is one joule per second. Multiply watts by 60 for joules per minute, by 3600 for J/hr, by 86400 for J/day.
Dividing an amount of joules by 3600000 (3.6million) gives kWh.
So, 100 W is 1/10 kWh per hour.

Note that the kWh is a unit of energy (3.6 million joules), not a unit of power (joules/unit of time).

Answer 2

The easiest way is to read the label on the ballast. If you can't get at it, assume the total lamp watts and add 25% for ballast loss. That won't be exact, but it will be close enough for most purposes. Example: a standard dual 40-watt fixture will pull about 100 watts total.

Answer 3

The bulbs that you will use are labeled with the wattage consumption, and the manufacturer normally include in print the electric consumption per month.

But remember every time you turn on the bulbs, the ballast needs to use more electricity to cause the florescent light to turn on, its the on and off that raises the electric consumption, sometimes you can save money by not turning the florescent bulbs off.

Time when you should turn on-off the florescent, it can help you maximize the life of the bulbs and keeps you in control of power consumption.