Updated on 04.24.10

Does a Motion-Activated Light Switch Save Money?

Trent Hamm

Paul writes in:

I’ve really been enjoying your recent cost breakdown posts. I’m thinking about installing a few motion-activated light switches in my home and I’m wondering if they will actually save me money. Which switches do you like? Will it actually save money in the long run?

Paul is referring to a motion-sensing light switch that will turn the lights on in a room when it detects any motion and will automatically turn the lights off after a certain period of time if there is no motion detected.

First of all, motion sensing switches do have some “phantom” energy use. According to this study, motion sensor switches use about a watt of energy on standby mode (23 hours a day) and 5 watts on active mode (about an hour a day). This trims a bit off of your overall savings. Over the course of a month, assuming your electricity costs the nationwide average of $0.11 per kilowatt hour, the switch itself will devour 0.84 kilowatt hours, or about $0.09 of energy. Month in, month out.

The model I’ve been recommended a few times is the Zenith SL-6107-WH, which sells for $22.90 at Amazon.com. You would want to prorate this over the lifetime of the switch – say, fifteen years. You’d effectively add a cost of another $0.13 a month for the switch. The switch thus has a cost of about $0.22 a month over the lifetime of the switch beyond what you currently have installed.

So, will you make that $0.22 a month back – and more? That cost is equivalent to the energy cost of leaving a single 60 watt light bulb on for 33 hours.

I wouldn’t install one in a heavy-traffic room, particularly one that has only one or two main lights (like our kitchen). In such a room, the switch would rarely flip off when there are people active in the house, because you would normally have it set to only turn off the lights after a lengthy period of no motion (say, 20 minutes or half an hour). The little bit you might save in having it flip off for ten minutes here and ten minutes there would not be a net savings over a month.

Where I would consider one is in a medium-traffic or low-traffic room, one in which you might accidentally leave the lights on for long periods without noticing. Closets. Guest rooms. Storage rooms. Utility closets. Bathrooms. This is particularly true if there are multiple lights on that switch.

In these rooms, traffic is very irregular and there can easily be periods of time where days go by without the lights being turned off. For example, the light fixture in our guest bedroom has four lights in it. If these all contained sixty watt bulbs and we left it on for a day, the energy use alone would have made the automatic light switch worth it in this case.

The room that I think would be the most effective for such a switch would be the bathroom. I can speak from experience that restroom lights are often left on, particularly in the evening hours. While these are usually “caught” before I go to bed, there’s often an hour or two of several bulbs burning, eating up the energy.

But there’s another factor at work here.

If you want to save money on energy costs in such low-traffic places, energy-efficient lighting is probably the smarter choice. Instead of investing $25 in a motion-sensing light switch to cut down on energy costs, install CFL or LED bulbs in such low-traffic rooms. Not only will the energy costs be lower while the room is actually in use, the penalty won’t be nearly as severe if you forget to turn off the light switch. For example, one CFL that produces light equivalent to a 60 watt bulb uses only 13 watts; an LED bulb (while more expensive up front) uses only 5 watts. This drastically cuts into the savings you would get from a motion-sensing switch, to the point that I wouldn’t find it worthwhile to ever install one to manage a single bulb.

In my own home, I would consider installing such switches is in the bathrooms and possibly in the utility room, the garage, and the guest bedroom – in other words, rooms with multiple lights on one switch that are used only in brief bursts with long periods of inactivity. Aside from that, I’m not convinced that such a switch would be a net savings.

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  1. Maureen says:

    We just use some inexpensive LED night lights in the bathrooms. It’s enough light for most midnight trips. I don’t really want to turn the overhead lights on anyway since it would make it harder to get back to sleep. Use your florescent lightbulbs in closets and garage so they won’t gobble up too much electricity if left on.

  2. Claudia says:

    So, if they are set to turn off with 20 minutes of no motion. What if you just go into a room for a minute? Sure, you can turn them off when you exit, but most people don’t. We have these lights at work, they frequently malfunction too, so they stay on forever. Or, if I go to throw a can in the recycling bin, they turn on. I’m just going two steps in the door of the breakroom to toss a can, I really don’t need a light on to do that. Sometimes going into the restroom, they don’t turn on, the door swings shut and one is left to fumble in pitch dark for the switch. I think they are more annoying than a savings.

  3. Hannah says:

    I can’t imagine why anyone would want to make their home more like a cold, sterile, office park with those switches. They make sense in an office because it’s no one’s job to make sure all the lights are off when the last person leaves for the night.

    You have to walk past the sensor to get the lights to turn on, and then if you sit still they go off. Not convenient for home. Plus all you’ll be doing is training yourself and your kids not to turn the lights off when you leave the room, which is really all you need to do to save the most energy.

  4. Noel says:

    I would consider such light at places like bathrooms. Few of my family members have habit of never switching lights off once they are done, leading to arguments. I am seriously considering such lamp. Thanks for the suggestion.

  5. Beth says:

    My parents have them outdoors, where I think is a smart location so their property isn’t brightly lit all night, but there’s still a little added security the add some extra light to supplement the solar lights they have.

  6. At work they replaced our old fluorecent light with a motion sensor and a smaller bright light that’s always on. Then when the montion sensor detect montion, it toggles on the big light for 5 minutes. I really have to wonder if the cost of replacing all the old light and putting these new ones in was worth it or not.

  7. jane says:

    I any actually install them in my closets espically the guest room ones that I use only for storage. I have left the lights on sometimes for days.

  8. ChrisD says:

    We had these at work. If you sat still for 10 mins or so they would switch off and you had to wave your arm around to switch them back on. One a time a work colleague started waving her arm around, but actually the sun had just gone in :). At home we have motion sensors for outdoors for the front door, the light switches off after about 3min.

  9. Dave M says:

    Do we really need motion detector lights inside the home? Have we really gotten that lazy? We have already automated so many aspects of daily life that we barely need to move or think at all. Don’t kid yourself into thinking that avoiding the mental burden of turning off a light will leave your brain free to cure cancer.


    I have a couple of them outside. They serve the purpose of switching on a light when I arrive after dark. They also serve a security purpose. If we notice an outside light coming on, we know something moved.

    They even help when the cat goes out at night: We know when he comes back.

  11. deRuiter says:

    Love all the comments since I haven’t tried one of these motion sensor lights, appears more PLASTIC psuedo green technoloby, you knw, “Buy this new plastic gadget and save the environment.” or “Junk you perfectly functioning apliance which is paid for and buy our new green piece of junk from China appliance on your credit card and save the environment.” hype. I’m reluctant to “buy” a lot of things for supposed “savings”, especially if I have a perfectly functioning something already. Energy saver aplianced don’t save all that much power and money over using what you’ve got. Most new tech stuff also destroys our balance of trade, another reason for not buying the latest iPad. CFL bulbs create toxic waste when tey break, and rather ugly harsh light when they’re in use. With bathrooms, we’ve got in the habit of turning off the light when we leave the room, just like all other rooms, it becomes a custom.

  12. Dawn says:

    We did install one of these in our kids playroom. We have nine canister lights (the floods) in there and if the kids forgot to shut the lights off, they could easily stay on for 12 hours without anyone noticing. We would notice when it got dark because the light would then shine out, but by then they could have been on all day. Our electricity bill did go down after we installed the sensor.

  13. michael bash says:

    I’m trying to understand; I really am. Why is it a problem for some people to turn off the lights when they leave a room? It should be second nature by the age of three. An automatic switch would be an added expense and a problem: if I leave a light on, that’s a decision and an accepted expense. Not turning off lights, it seems to me, is indifference, irresponsibility, disobedience on the part of children or all of the above. RSVP if you want.

  14. Kristen says:

    Another factor with a light switch like this is safety and convenience. I installed one in my laundry room, which also doubles as a storage area. I’m constantly walking into the room with my hands full, so it is fantastic to have the light switch on automatically. I also have the sensor set to much less than 20 minutes after motion stops for the light to turn off– it turns off after about 2 minutes.

  15. Sonya says:

    my current home came w/ one of these in the entry- which is also the path to the kitchen… gets a lot of use. At first I thought- fantastic- no coming in to a dark hallway… then I lived with it for a week. Thankfully mine has an off setting, because it made me batty! Aside from being a section you pass through often en route to the kitchen, and it would sometime trip going to the neighboring bathroom, I also have 2 cats (and currently 5 kittens- anyone want a kitten?) so they trip it all the time. Sitting in the living room with the light going on & off was maddening! So yeah, in a garage it could be handy (I always have my hands full in there it seems, no switches would be great) but I wouldn’t put them many places in the house personally.

  16. Brian says:

    I’m thinking in my basement. My wife goes down there sometime mid-day while I’m at work to do laundry. Often times I don’t realize she’s left the light on until we’re going to bed and I see it shining under the door.

    Of course, this light would require re-wiring, it’s currently a pull string fixture and would have to be wired to a switch, probably by the door…. In which case she likely wouldn’t leave it on anyway.

  17. Brent says:

    Only place I could see using this is the garage. Sometimes I forget it. But I don’t think I’ve even gotten close to the break even in waste. You have to be really forgetful. changing out my garage door opener would net me more savings.

  18. This is a great topic that hits close to us, since this is the niche our business operates in!
    Truthfully, I agree with most of you. Learning to flip a switch is not rocket-science. I can see the trouble with the pull-chain in the basement with a full load of laundry in my hands! But, as you stated, wiring the switch alone would save you.
    We install the full-blown home automation systems and for that we utilize the motion detectors. There’s a computer board of some kind that controls the light switch (we love HAI) but I think it is a much better solution, albeit much more expensive and not viable for retrofit unless you’re essentially gutting your home. That way your cat/dog won’t accidentally trip the light because if you have one, we’d be installing motion detectors with pet immunity so they don’t also trip your alarm! They are programmed to go on/off at certain times and people use them for the ‘lived-in’ look while away. It gives more flexibility than just a store-bought ‘on for x number of hours after dark’ timer.
    In most homes, though, I don’t see the use and even here, the only time we utilized one (to test out functions and learn programming) was for the opposite reasoning! We had our bathroom light in what was our bedroom come on at night so that we weren’t walking into a dark part of the house fumbling for a switch and possibly tripping over something. (like one of our 4 cats)
    Like most of the commenter’s so far, I also hate walking into commercials bathrooms and such where they have these and they malfunction. It makes me want to hand someone at the desk my business card. :-)

  19. Claudia says:

    If you live in the country, the outside lights come on continually as deer, skunks, racoons, squirrels, etc run around your yard at night. It can be very annoying.

  20. Bobby says:

    I can’t tell you how many times this question get’s posed to me when people are buying replacement bulbs . My advice has always been ask yourself if it’s right for you. If you are the type of person that is habitual in turning off lights then this probably isn’t the right choice however if you’ve never had the discipline to turn off lights then this would be a wonderful solution.

  21. Charles Cohn says:

    For my wife and myself, such lights are very useful. When you go to sleep, you need to have all lights off and the room pitch dark for best sleeping. When you get up and move about, though, you need light for safety. Unless you have a light switch right next to your bed, you will be fumbling around in the dark for a while. The motion-detector light eliminates that fumbling.

  22. Sm4k says:

    We have one in our utility room, where my wife is frequently carrying clothes baskets in and out of with full hands. We’ve had the light on all night long on more than a few occasions, so we put a motion sensor light in.

    However, the switch we used cannot work with most CFL ballasts. We probably would have been better off with an LED bulb.

  23. mrdavidhsmith says:

    I don’t think saving money is the best motivation for using sensor lights. Their real value is in security and scaring cats out of the yard. That said, I save heaps by running sensor lights. Some of the light switches in my old house are in illogical places- you have to walk across the room to reach the switch. Running a sensor light costs way less than fitting new switches, and is much nicer for visitors and children going to the bathroom. I imagine similar uses in stairwells.

    I’ve never had a closet big enough to warrant a light- but wouldn’t a switch in the door (like fridges have) be a better alternative?

  24. FrankMi says:

    I have used these devices for years in specific locations and have been very pleased with the benefits. In the powder room it addresses the reoccurring issue, particularly with kids, of not shutting the light off. For normal bathrooms however, a light and motion sensing night light makes more sense. The same type of night light works well in hallways and near stair ways, particularly for guests using the facilities in the middle of the night as they are less likely to have a good feel for the home’s layout and don’t want to be blinded at 2AM! I also install motion sensor switches at the top and bottom of normally dark stairways so that I don’t have to set down the things I may be carrying in both hands in order to see the stairs. The third location that makes sense for me is in garage (or any other windowless area) where you may have your hands full as you enter or leave the room. For closets, pantrys, and other storage areas however, a door activated light switch may make more sense.

  25. Mike says:

    Great breakdown, amazing what some simple calculations and logic can do. I’ll admit, I have had the same cost/benefit question about motion lights on my mind for some time. My kids are like most kids and have a severe aversion to shutting of lights.

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