How energy efficient is a fluorescent bulb and how much does it cost to run one 5ft fluorescent bulb 9hrs a day for the average business year excluding weekends bank holidays etc in british pounds?

The formula is (bulb watts x ballast power factor) x hours / 1000 = kWh

Cost is simply kWh x gbp

For example: Your light bulb is 60 watts, evidenced by the writing on the bulb saying... 60 watts. However, fluorescent lights have a ballast, which is a type of transformer. Each ballast converts the input voltage to something usable by the fluor. bulb. In the case of modern electronic ballasts (vs. magnetic), the power factor ranges from .65 - 1.0. You can get this info from the manufacturers website. For this demonstration, we'll use .88, which is the standard power factor in the US for the big 3 ballast manufacturers.

Next calculate your hours, for the energy industry, we accept 2080 hours for office buildings. This covers janitorial staff, weekend workers, etc.

So, we have (60*.88)*2080/1000 = 5798 kWh ?? The answer I get is 109.824 kWh when using the above formula. Where did 5798 come from ??