The winters are dark and cold here in Minneapolis, and I had not been not happy with our outdoor lights.  They got my attention because we were advised by the police to keep them on all night after a recent burglary.  So, in the winter, they are on from about 4:30 pm until 6:30 am — 14 hours per day.  The fixtures themselves are okay, but the bulbs that came with them are 50-watt halogen spot lights.  With CFLs and LEDs offering lower wattage options (and their color and quality continuing to improve), I decided to do a little comparison shopping.

Light bulb comparison can be tricky — you have to understand the concept of “lumens” as well as the “color” (K factor) of each light to be able to compare them on an apples-to-apples basis.  People tend to think that wattage represents how bright a bulb is (as in, a 100 -watt bulb is much brighter than a 50 watt bulb), but that is no longer the case since CFLs and LEDs were introduced to the market.  The brightness of the bulb is represented by “lumens” – so when you comparison shop, that’s what to look for.   The K factor is the “color” of the light.  LEDs used to have more of a bluish tint, but they have become softer and more like incandescent bulbs.

I have a strong preference for LEDs over CFLs.  CFLs have mercury in them and have to be disposed of properly as a hazardous material.  LEDs do not have mercury, are lower wattage than CFLs, and last longer.

I was pleased to have found some LED EcoSmart bulbs at Home Depot.  These 8.6 watt bulbs cost $9.97 each, provide 429 lumens (similar to our existing bulbs), and last 50,000 hours.  I compared them to three different options:

1. 50 watt halogen bulb (what I am replacing): This 50-watt bulb is $7.47 at Home Depot, provides 520 lumens and lasts 3,000 hours.  These are the bulbs currently in our outdoor fixtures.  (According to the box, 3,000 hours is equivalent to 2.7 years — which means they assume the bulb is turned on 3 hours per day.  Realistically, though, they are on about 14 hours per night in the winter and maybe 7 in the summer, for an average of 10 hours per day.)
2. 40-60 watt incandescent bulbs (the cheapest bulb):  The 40-watt and 60-watt bulbs have lumens of 360 and 630, respectively (so about in the middle of the LED’s 429 lumens).  A 6-pack of these incandescent bulbs goes for $7.97 ($1.33 each), and they last 1,000 hours.
3. CFL bulb (a necessary comparison, because of its low wattage):  These 14-watt compact fluorescent lights have an output of 450 lumens, last 8,000 hours, and cost $10.97 for a two-pack ($5.49 each).

So…how do the LEDs compare to these three different options?  Other than the initial expense, 2 other costs need to be factored in:

1. The life of the bulb.  Since I am comparing the LED bulb to the others, that is my base case.  The LED lasts 50,000 hours.  So, the proper comparison is how many times I will need to buy another light bulb over that timeframe.  I’ll assume the costs of the various bulbs stay constant.
2. The cost of energy.  To get to this, you have to look at your electric bill and find out how much your are charged per kilowatt hour (kwh).  One kilowatt hour = a 100 watt bulb turned on for 10 hours (which equal 1,000 watt hours, which is the same thing as one kilowatt hour — or kwh).   In Minnesota, our utility rate is about 9-10 cents per kwh.  I’ll assume that rate stays at 9 cents over the years, though it is likely to go up (which would make the case for LEDs even stronger).

The following table compares the lifetime costs of the LED bulb to the other 3 options:

So, while the initial cost is higher, the ongoing operating costs (electricity) are lower.  Here’s how the analysis looks, comparing the incremental costs to the LED:

*calculated by taking the difference in lifetime energy costs + lifetime replacement costs, less the initial cost of the LED bulb.

The LED comes out a clear winner, even above the CFL.  Compared to a CFL, I’d save almost $50 per bulb; if I have 6 bulbs, that’s $300 – and worth the trip to Home Depot!

It doesn’t really matter how many hours per day you use your lights–the lifetime cost comparison is the same. The only thing that changes is how quickly the LED pays for itself.   If the bulb is turned on 1 hour per day or less, the energy and replacement costs barely make it worth it.

In our case, though, we average 10 hours per day, and we replaced halogen bulbs.  So, we save $13.60 in energy costs per year, and avoid $124.50 in replacement costs over the next decade.  Our payback in energy savings alone is a little over 2 months!  Now, if we had the lights on for only 3 hours per day, it would take a little more than 7 months for the energy savings to pay for the incremental cost of the LED bulb.  What a deal!  I’m surprised Home Depot can keep these bulbs on the shelves.

If we were to consider the other bulbs, our payback would be 7.6 months in energy savings alone compared to a 50-watt incandescent; 30.2 months compared to a CFL.  And that does not include replacement costs.

Another note: Nowhere do I include the benefit of the time and energy needed to go buy more bulbs and replace them every year.  Surely this is worth something – at least emotionally!