How does one calculate the cost of operating a light bulb?

Update: 2018-01-19 15:01:54

To calculate the cost of operating a bulb for one day - multiply the bulb wattage times the hours per day the bulb is used, divide by 1000, and multiply by the Electric Company's cost per kwh.

For example: 100 watts x 5 hours divided by 1000 x US$ 0.10 = US$ 0.05.