The eternal light question

[GpsFrontier]

Isn't this a question on lighting?

No,
The question is about calculating electricity cost. Just because it's referring to lighting makes no difference. You calculate energy consumption using the same formula whether it's a light, refrigerator, radio, TV, computer, electric fan, pond pump etc. That is not an opinion, they teach Ohm's Law (current (amps), volts and Resistance are the 3 parts of electricity) in school, although it has been a lot of years sense I was in school. Watts is a measurement of the rate of energy conversion, and if I remember correctly is also a measurement of the heat generated by that conversion. No where is lumens (a measure of the power of light perceived by the human eye) mentioned as any measurement (or part of) of electricity.

Once the amount of energy used is determined, then it can be multiplied by the price per Kilowatt that the electric company charges (easily found on your electric bill).