A $70 light bulb???

There is a lot of talk around the world about compact fluorescent bulbs. They save energy. They also contain mercury and can be big. They just don’t fit in a lot of my fixtures. So I keep checking the prices of LED bulbs. Here is a little math to see whether or not a $70 LED bulb is a good replacement for a $7 Halogen flood… (If you really, really, really don’t want to read about the math, skip to the end for the final result…)

First, the purchase cost: $70 vs $7. I looked at a LED bulb with a similar light output — 480 lumens vs the light output of my existing halogens — 550 lumens. The halogen is rated at 2500 hours, the LED at 100,000. 40 times the life for 10x the cost. So it would take $7 x 40 or $240 of halogen bulbs to last as long as one LED bulb. That’s a savings of $240 – $70 or $170. Looks good so far…

Now for the operating cost. Over the lifetime of one LED bulb the operating cost at $0.10/kWh is [dollars/kWh x kW x Hours] which is 0.10 x (.01) x 100,000 or $100.  The operating cost for the halogen 5 times greater — it uses 50 watts instead of 10. So the cost is $500. That makes the operating savings over the life of the bulb $400.

Combine the operating savings and the purchase savings and that makes a total of $170 + $400 or $570 over the life of the LED bulb.

Now let’s look at one year of use: I use the lights in my kitchen. I’m guessing about 2000 hours in a year, but let’s use the life of the halogen, or 2500 hours as a close comparison. FIrst, the purchase cost. The halogen is $7. One fortieth of the LED is $70/40 or $1.75. That’s a savings of $5.25. We’re off to a good start.

Now the operating cost. For the halogen its 2500 hours x 50 w = 125 kWh. At the same $0.10/kWh we used above  that’s $12.50 to run the halogen bulb for a year. The LED is 2500 hours x 10 w = 25 kWh (one fifth of the watts, so one fifth of the kWh) or $2.50 to run the LED bulb for a year. A savings of $10/year. So in one year we saved $15.25 per bulb.

My kitchen has 14 halogen bulbs. That would cost $970 to retrofit! The savings would be $213 in the first year. So it would take four and a half years to pay back the cost of the bulbs, not including the environmental benefits.

Over the life of the LEDs, though, I’d save 14 x $570 — almost $8000!

They say the price of LED bulbs is coming down. I can also get cheaper LED bulbs, but I’d have to use more of them. In fact, to save money on the LEDs I’d need twice as many; that would mean more track fixtures for my kitchen. Still it would mean a comparable, maybe even larger, overall savings. It may be time to convert to LEDs.

This entry was posted on Sunday, July 20th, 2008 at 5:07 pm and is filed under Home energy saving. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.