I saw a piece on CBC Newsworld saying that compact fluorescent lamps (CFLs) don’t save as much money as many people claim. The piece made the explanation seem mysterious and complicated, but it’s quite simple. The problem with the standard analysis is that it ignores secondary effects.
The relevant secondary effect here is heating. All energy absorbed by a light bulb ultimately turns into heat. Even the light produced will bounce around off objects and eventually turn into heat. So a light bulb inside your house is like a mini electric heater. A tiny fraction of the light might escape through a window, but for practical purposes, 100% of the energy heats your home.
Here’s an example of the standard analysis of savings. Suppose that you replace a 60-Watt incandescent light bulb that gets used 6 hours per day with a 15-Watt CFL. Power consumption drops by 45 Watts for 6 hours per day. This saves a total of 8.2 kilowatt-hours per month. Assuming a cost of 12 cents per kilowatt-hour, you save a hair under a dollar each month, or $12 per year.
A real analysis that factors in heating gives a different result. The simplest case to analyze is a house heated with electricity. During the heating months the electric heaters will have to make up the lost 45 Watts of heat that used to come from the incandescent light bulb. This exactly offsets the CFL’s supposed savings. The net savings during heating months is exactly zero.
During months requiring no heating or air conditioning, you will save the dollar each month. However, you may heat your home a little longer into spring if you’re not getting as much heat from light bulbs. This effect should be fairly small.
During months where you use air conditioning, you actually have to spend extra money on air conditioning to get rid of the heat created by light bulbs. So, the savings from using a CFL are more than a dollar per month.
Overall, the yearly savings will depend on how many months you heat and use air conditioning, but in a Canadian climate the total savings per year will be less than the $12 from the simple, but flawed analysis.
Another complication in this analysis comes if you use non-electric heating such as natural gas. As it happens, the total cost per unit of energy from electricity and natural gas for me are both about 12 cents per kilowatt-hour once you take into account all the extra charges and taxes. But, if the natural gas were more expensive than electricity, then the CFL would actually lose money during heating months.
One situation where CFLs are a very clear winner is in outdoor lighting. In this case the heat generation is irrelevant, and the cost savings of CFLs are significant. If you haven’t tried CFLs yet, you may want to start with your outdoor lights.