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How much money does turning off the lights really save?

For short durations, it's not worth the effort, blogger says.

By Karen Datko Oct 12, 2009 12:48AM

This post comes from Trent Hamm at partner blog The Simple Dollar.

When I was young, my parents were adamant about turning off lights, and would be rather upset with me when we'd go on a two- or three-day trip and my bedroom light remained on.

My wife and I go through the house and turn off lights, sometimes even if we're just leaving for a couple hours.

Is this tactic worth the time invested in it? Let's crunch the numbers, but let’s first make a few assumptions.

  • It takes two minutes to walk through the house and ensure all the lights are shut off. From the upstairs bedrooms to the laundry room on the far side of the basement, that's about right for our house.

  • Electricity costs 10 cents per kilowatt-hour. That is roughly the nationwide average, and roughly what we use.

  • The average bulb in our home eats 20 watts. We use mostly CFLs. At my parents' home, where most bulbs are incandescent despite my admonitions, the average is 50 to 60 watts per bulb.

  • On average, I turn off four light bulbs during the walk-through.

Taking those assumptions, let's say we’re going on a two-hour trip. I turn off four 20-watt bulbs that would have run for two hours, so that’s a total of 160 watt-hours of energy. The savings from that two-minute walk-through is 1.6 cents.

Let’s do the same for an average workday, when the house will be empty for nine hours. Turning off four 20-watt bulbs saves 720 watt-hours of energy or 7.2 cents. This is getting better, but still not very cost-effective.

Let’s look at a weekend trip, which we take about once a month. We’re typically gone for about 52 hours. If we turn off those same four 20-watt bulbs, we save 4,160 watt-hours of energy. That’s 41.6 cents, which is getting to be worthwhile for two minutes of effort.

What if other electronic devices are left on? A television uses 150 watts on average. Over two hours, that’s only 3 cents. Over that 52-hour trip, that’s 7.8 kwh, or 78 cents.

Here’s what I concluded from running the numbers.

A walk-through gets more cost-effective the longer your trip is. For very short trips, it’s probably not worth the time investment. With just the light bulbs and a two-minute walk-through before a two-hour trip, your hourly wage is 48 cents. However, if you do a two- minute walk-through before a two-day trip and find four lights and a television on, your hourly wage for that effort is $35.88.

The more devices you turn off, the more worthwhile the walk-through is. On longer trips, I unplug devices, power off everything on my entertainment center, and unplug my laptop’s power supply. This can be done pretty quickly, not adding much to the time of the walk-through.

My strategy? On short trips, I may not bother with a walk-through -- it’s not worth the time. On weekend trips, I’m vigilant about a walk-through to turn things off and unplug others. It saves a lot of energy, and the value of the time I invest is quite worthwhile. I can earn the equivalent of a $50 hourly wage turning stuff off before a long trip.

Simple things like these make a difference. Taking a few minutes to look at your behavior and realize when a frugal tactic is cost-effective can tell you whether that behavior is right for you. I try to look at it as an hourly wage. If that hourly wage looks nice to me -- or there’s some other appeal -- I’ll do it. That's why when I bake bread, I usually make several loaves at once, and also why I enjoy trying once-a-month cooking. But I usually eschew  high-intensity efforts to collect coupons. I’ll browse through them at the kitchen counter on a lazy Sunday morning and sometimes search online for them, but the benefit is usually not worth the effort.

Other articles of interest from The Simple Dollar:

Published Nov. 30, 2007


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