Understanding Power Use (Watts) and Power Cost (kWh)

Recently I upgraded my kitchen lighting from halogen to LED bulbs as the latter have become very inexpensive (especially with PSE instant rebates). But as always I was curious about the value of upgrading bulbs.

As you know lightbulbs show you power consumption in watts, but power bills are in kWh (kilowatt hours). Put simply if you took a 1000 watt device (1kW, like a blow dryer) and ran it for an hour, you’d use a kWh.

Now in the case of a blow dryer the high wattage isn’t much a concern since the time used each day is small (and I shave my head anyway…to save power of course…). But the kitchen lighting for instance had six 75 watt bulbs, which are often on for hours each day in our household. That means 450 watts (.45 kW) and we guessed 2-4 hours of use per day. So assuming 3 hours a day of use that’s 40.5kWh/mo (.45kWh * 3 hours/day * 30 days/mo). I pay 10.5¢/kWh for power so that means $4.25/mo to run the kitchen lights.

In the case of the kitchen I replaced the bulbs with 9.5 watt LEDs, so running for the same 3 hours a day for a month lighting the kitchen costs just 54¢.

Admittedly saving $45/year isn’t a huge deal, but for spending just $13 in new bulbs its not a shabby deal either – if someone offered to trade your $13 in cash in exchange for their $45 in cash, you’d take that offer every time! Even better next year that same person will give you another $45 for nothing!

Not to forget each kWh saved in PSE territory means about a pound of CO2 saved – over a year you’ll save 420lbs of CO2.

Perhaps more than anything the benefit of LEDs is helping to not make new power plants.

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