How to Calculate the Energy Cost for a Light Bulb
- 1). Determine the wattage of the light bulb. The wattage is clearly marked on the bulb. You may have to unscrew the bulb from the fixture to read the wattage.
- 2). Determine the time (in hours) that the light bulb is typically on per month. A simple estimate can be determined by taking the average time the bulb is on per day and multiplying that time by 31. For example, a bulb that is on 10 hours per day would be on a total of 3,100 hours per month (10 x 31).
- 3). Multiply the time the bulb is on per month (in hours) by the wattage of the bulb to determine the total wattage used per month. For example, a 100 watt bulb on for 3,100 hours would equal 310,000 watts.
- 4). Divide the total watts used per month by 1,000. This will give you the total kilowatts used per month. For example, 31,000 divided by 1,000 would equal 31 kilowatts used per month.
- 5). Multiply the total kilowatts used per month by the cost per kilowatt charged by the electric company. This value is shown on your monthly electric bill. This will give you the total cost of the light bulb per month. For example, if the cost of electricity is 10 cents per kilowatt hour, then 31 times $0.1 would equal $3.10 per month.
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