Turn Off the Lights to Save Money…But How Much?

When I was young, my parents were adamant about turning off lights and were often rather upset with me if we’d leave on a two or three day trip and my bedroom light remained on. Even now, my wife and I traditionally go through the house and turn off lights, even if we’re just leaving for a couple hours.

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

My Energy Usage Assumptions

1. 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, this is about right for our house.

2. Electricity costs $0.10 per kilowatt hour.

This is roughly what the nationwide average is, and roughly what we use.

3. The average bulb in our home eats 20 watts.

We use mostly CFLs, so this is a rough estimate. At my parents, where they’re still using almost all incandescent bulbs despite my admonitions, it’s more like 50-60 watts on average per bulb.

4. Doing that walk-through causes me to turn off four light bulbs.

This is just on average, sometim es more, sometimes less.

Taking those assumptions, let’s say we’re going to leave 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, or 0.32 kilowatt hours. The effort in that walkthrough, which takes two minutes, is 1.6 cents.

Let’s do the same for an average work day, where the house will be empty for nine hours. Turning off four 20 watt bulbs that would have run for nine hours saves 720 watt hours of energy. That two minute walkthrough here saves 7.2 cents. This is getting better, but still not very cost effective.

Now, let’s look at a weekend trip, which we take about once a month. We’re typically gone for about 52 hours. Thus, 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.

This is assuming only lights, of course. What about the potential for other electronic devices to be turned on? If you find a television on, which sucks down roughly 150 watts on average. Over two hours, that’s only 3 cents. Over that 52 hour trip, that’s 7.8 kilowatt hours, or $0.78.

Can You Turn Off the Lights and Save Money?

Here’s what I concluded from running the numbers.

1. A walkthrough gets more and more cost effective the longer your trip is going to be.

For very short trips, it’s probably not worth the time investment – with just the lightbulbs and a two minute walkthrough before a two hour trip, your hourly wage for that effort is 48 cents. However, if you do a two minute walkthrough for a two day trip and find the four lights and the television on, your hourly wage for that effort is $35.88.

2. The more devices you turn off, the more worthwhile the walkthrough is.

On longer trips, I do things like unplugging devices, powering off everything on my entertainment center, unplugging my laptop’s power supply, and so on. This cuts down on a lot of drain and can be done pretty quickly, not adding much at all to the time of the walkthrough.

My strategy? On short trips, I usually don’t even bother with a walkthrough – it’s not worth the time. On weekend trips, however, I’m pretty vigilant about a two or three minute walkthrough to turn things off and unplug a few things – it saves a lot of energy and the value of the time I invest in it is quite worthwhile (I can regularly earn the equivalent of a $50 hourly wage turning stuff off before a long trip).

Conclusions

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

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