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Energy Efficiency

Published on February 23rd, 2011 | by Susan Kraemer

18

LEDs v. Incandescent Bulbs – the Math

February 23rd, 2011 by  




I have a mental block about the upfront cost of LEDs, that is like the block most people have about solar.

(To me it seems so obvious that solar electricity is cheaper than utility electricity in my state that I get frustrated that every roof doesn’t sport solar. It’s as if people have some kind of a mental block about solar. They think it’s a good thing – for some time in the future, and of course, they mean to do something about their energy choices – some time in the future, sure, but in the meantime…)

But I have to confess, I am just like that – when it comes to LEDs. Sure I know they are cheaper in the long run, and are more efficient by a very long shot than incandescent lights (about a tenth the energy needed to make the same light), but somehow I can’t get over the upfront cost. And there’s no PPAs or leases for LEDs, obviously,  like there are for solar, to eliminate that “oh, but the upfront cost!” argument.

But some math from Marc Gunther at Greenbiz has provided the evidence needed to change my mind. Let’s see if it does.

First take a conventional 60 watt bulb. Take the equivalent in an LED – which uses only 12.5 watts, while providing the same amount of light. Now compare the electricity costs between the two, run for the duration of a 25,000 hour period, which is nearly three years if run 24/7, or about 12 years if run 6 hours nightly.

If you pay 12 cents a kilowatt hour, electricity will cost $37.50 to run the 12.5 watt LED for the 25,000 hours. But you will pay $180 to run the 60 watt incandescent the same amount of time.

That is one saving right there, the cost of electricity.

But another saving is this. Only the LED will actually last the 25,000 hours which is about 12 years if you are turning it on at 6PM every night and off at midnight. However, the incandescent bulb will only last 1,000 hours, so one bulb actually cannot even do this test.

Instead you’d need to buy 25 incandescent bulbs to stand up to the duration of one LED bulb to run this 25,000 hour test.

We long ago replaced all our incandescent bulbs in our house with CFLs, and that math is not so extreme – but we are moving this year. So the choice will come up again for us. Next time I look at an LED and think, “but it’s so expensive”, I think I will consider this math.

It really doesn’t seem quite so expensive any more. Especially if you pay a higher rate than the average for electricity.

Susan Kraemer@Twitter 
 





 


About the Author

writes at CleanTechnica, CSP-Today and Renewable Energy World.  She has also been published at Wind Energy Update, Solar Plaza, Earthtechling PV-Insider , and GreenProphet, Ecoseed, NRDC OnEarth, MatterNetwork, Celsius, EnergyNow, and Scientific American. As a former serial entrepreneur in product design, Susan brings an innovator's perspective on inventing a carbon-constrained civilization: If necessity is the mother of invention, solving climate change is the mother of all necessities! As a lover of history and sci-fi, she enjoys chronicling the strange future we are creating in these interesting times.    Follow Susan on Twitter @dotcommodity.



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