An Electric Lighting Audit

A while back I did an energy audit in my house. Fortunately for me I do live in an area served by cheap hydroelectric and coal energy. Well, fortunately for my pocketbook anyway. Regardless, I'm ever attempting to reduce my energy needs for both personal and altruistic reasons, hence the audit.

I surveyed all the lights in my home, noted their location, type, wattage, etc. When we moved in, most of the lights were old school incandescents. Altogether they added to 2918 watts of lighting. By swapping in a few compact fluorescents I've reduced that total to 1778. That's a savings of 40%. Impressive, but not so fast. Are all those lights used the same amount? Definitely not. The garage lights are on for probably only 10 minutes per day, on average. So clearly we need to factor actual usage into the equation.

So I also estimated the average usage of each bulb. Yes it was as fun as you think. What I found is that our 2918 watts account for about 4950 watt hours of actual usage per day. After my upgrades that dropped to 3274 watt hours, for a savings of 34%. If you notice that's less than the 40% we calculated earlier you get a brownie point. Indeed some of the lights we use the most are ones that I cannot reduce any further.

Even more interesting is something I've recently come to understand as I make a concerted, although to many unquestionably bizarre, attempt at understanding statistics. Quite often a very small number of things will often account for most of your results. A good example is the US federal budget. While McCain notably complained about earmarks in bills (which may be undesirable for many reasons) they account for a very small fraction of the money spent. If you want to make any reasonable dent in the outlays your best bet is defense, social security and medicare/medicaid which account by themselves for 65% of our expenditures.

Getting back to the original point (and hopefully avoiding a political tangent), I found that just a few of the lights in the house account for the majority of the electrical usage. In fact, the two sets of fluorescent lights in the family room account for nearly 60% of the total electricity. Even if I were to upgrade the rest my bulbs to compact fluorescents, it would only decrease my current usage by another 15%. I'm pretty much bound by those two sets of lights.

The exercise was a useful one. I'm on a slow quest to analyze all the electrical usage in the house. The light bulbs were the easiest to tackle. Some time I'll move on to the appliances and computers. The latter I'm rather apprehensive about. I might rather be ignorant.

My data files: format
CSV format



You might try investigating

You might try investigating LED light bulbs. The last time I researched them they didn't seem too great, although I've heard of some people using them recently. They screw into standard light bulb sockets, but instead of having an incandescent filament or a mercury plasma they are simply a bank of LEDs. If an ordinary incandescent bulb has life l, cost c, and power consumption p, then roughly speaking, a CFL has life n*l, cost n*c, and power consumption p/n, for any n ~ 4-6. Similarly an LEd bulb has n^2*l, n^2*c, and p/n^2.

Anything with a heating element in it will use more electricity than an incandescent light bulb. Curling irons use about 1500 W, toasters, space heaters, electric ovens, etc. From what I remember an idle desktop computer will consume energy at the rate of 60-90 W, so unless you're burning DVDs all day that would probably be minimal. If you decide to measure your total energy use instead of just your total electrical energy use you will want to consider the amount of energy used, and wasted, by your furnace and water heater, obviously.

Re: You might try investigating

So far LED lights have been quite expensive and not as reliable as other options, but I'm hopeful that I may be able to use them sometime. That would work well for my office whose light is on 11+ hours a day. But the big user is the family room and that's a traditional fluorescent light (4 40W bulbs). To decrease the usage there would require a pretty major overhaul, which we'd like to do since the lights are pretty ugly, but it ain't gonna happen soon.

Our heat and water are gas fired, so that makes the electrical calculation easy. I have grand plans to itemize all the electrical devices in the house. I have a Kill-A-Watt to assist in the measurement there.

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