Anonymous
Anonymous asked in Science & MathematicsEngineering · 8 years ago

# How much does it cost to run one 13W bulb 24/7 for 30 days at \$0.090/KWH?

I did the math myself but I don't know if I was right or not.

Update:

Tell me if my math is correct:

There are 720 hours in one 30-day month.

1 Watt = .001 KWH

1 Watt x 720 = .720KWH

13 Watts x .720 KWH = 9.36 KWH

9.36 KWH x \$0.090 = \$0.84

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So my math says that one 13 Watt light bulb costs \$0.84 (84 cents) per month to run 24/7 at the rate of \$0.90 per KWH.

Is this correct?

Update 2:

So if I leave two 13W porch lights on during the day AND night, then the extra cost is:

Gets dark: 8:45pm

Sunrise: 5:45am

Extra hours: 15 hours extra

15 hours x 30 = 450 hours extra each moth for each bulb

2 bulbs = 450 x 2 = 950 extra hours for two bulbs

.950 KWH/mo x 13W = 12.35 KWH/mo

12.35KWH x \$0.090 = \$1.1115/mo

So the extra cost for leaving the porch lights on all day is \$1.11 per month.

In one year, it costs less to leave on the porch lights than it costs for the actual bulbs!!!

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• 8 years ago