# Motion Sensor for Fluorescent Lights **URL:** \ **Category:** Factual Questions\ **Created:** [March 13, 2013, 2:49pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823 "2013-03-13T14:49:09Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![dolphinboy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dolphinboy/32/330_2.png) [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)\ **Post date:** [March 13, 2013, 2:49pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/1 "2013-03-13T14:49:09Z")
My wife wants me to add a motion sensor to our bedroom closet so that the light goes one when you enter and goes off after some period of time if nobody is there. (We have a relatively new fluorescent fixture in the closet tha I would rather not replace.) So I went to my local Home Depot and they said that the ones they sell don’t work with fluorescent lighting for some reason. He didn’t say exactly why they didn’t work. Does somebody somewhere make a motion sensor switch that does work with fluorescent lights? ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [March 13, 2013, 2:59pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/2 "2013-03-13T14:59:17Z")
Huh? Our workplace a while ago put in motion sensors (Wall switch replacement) that included a sensor. This lead to exactly the scenario in the workplace joke, if you are just sitting there typing, the lights will go out and you have to flap your arms. (No, they didn’t hire an intern to walk around waving their arms). So they do make them. ---
**Author:** ![Antigen](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Antigen](https://boards.straightdope.com/u/Antigen)\ **Post date:** [March 13, 2013, 3:06pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/3 "2013-03-13T15:06:04Z")
Weird… we have a fluorescent fixture in the laundry room and my husband put in a motion sensor last year and it works great. I’ll check what brand it is when I get home tonight. ---
**Author:** ![Lukeinva](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lukeinva/32/17872_2.png) [@Lukeinva](https://boards.straightdope.com/u/Lukeinva)\ **Post date:** [March 13, 2013, 3:26pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/4 "2013-03-13T15:26:02Z")
> [@md2000](#): > > Huh? Our workplace a while ago put in motion sensors (Wall switch replacement) that included a sensor. This lead to exactly the scenario in the workplace joke, if you are just sitting there typing, the lights will go out and you have to flap your arms. (No, they didn’t hire an intern to walk around waving their arms). > > So they do make them. Yup. At my work the room where the big communal printer/xerox/fax/scanning machine is located has motion-sensor flourescent lights. ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [March 13, 2013, 3:48pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/5 "2013-03-13T15:48:30Z")
I bet he was thinking of dimmers, they often don’t work with fluorescent lights. ---
**Author:** ![SmellMyWort](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@SmellMyWort](https://boards.straightdope.com/u/SmellMyWort)\ **Post date:** [March 13, 2013, 3:56pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/6 "2013-03-13T15:56:58Z")
This [switch](http://www.smarthome.com/2522W/Leviton-PR150-1LW-Single-Pole-Wall-Switch-PIR-Occupancy-Sensor-White/p.aspx) should work but it says your light needs to have an “instant on magnetic ballast.” If you look at the different switches at your home store you’ll see some labeled for incandescent and others labeled for LED/florescent use. ---
**Author:** ![dolphinboy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dolphinboy/32/330_2.png) [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)\ **Post date:** [March 13, 2013, 4:55pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/7 "2013-03-13T16:55:53Z")
> [@SmellMyWort](#): > > This [switch](http://www.smarthome.com/2522W/Leviton-PR150-1LW-Single-Pole-Wall-Switch-PIR-Occupancy-Sensor-White/p.aspx) should work but it says your light needs to have an “instant on magnetic ballast.” If you look at the different switches at your home store you’ll see some labeled for incandescent and others labeled for LED/florescent use. How do I know if I have an “instant on magnetic ballast”? Can I assume I do? ---
**Author:** ![campp](https://avatars.discourse-cdn.com/v4/letter/c/c5a1d2/32.png) [@campp](https://boards.straightdope.com/u/campp)\ **Post date:** [March 13, 2013, 5:32pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/8 "2013-03-13T17:32:18Z")
Yeah, I bought a regular security light, and swapped out the overkill incadescent lamps with flourescent ones. It’s been working fine for years. ---
**Author:** ![SmellMyWort](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@SmellMyWort](https://boards.straightdope.com/u/SmellMyWort)\ **Post date:** [March 13, 2013, 6:41pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/9 "2013-03-13T18:41:56Z")
> [@dolphinboy](#): > > How do I know if I have an “instant on magnetic ballast”? Can I assume I do? I’m not sure. You could just get a switch that says it works with florescent lights and see if it works. Or you could examine any documentation that came with the fixture. Or you could examine the fixture itself. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [March 13, 2013, 6:48pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/10 "2013-03-13T18:48:30Z")
> [@dolphinboy](#): > > How do I know if I have an “instant on magnetic ballast”? Can I assume I do? This question is discussed some here: [http://handymanwire.com/ubbthreads/ubbthreads.php/topics/467588/Instant\_on\_magnetic\_ballast\_fl](http://handymanwire.com/ubbthreads/ubbthreads.php/topics/467588/Instant_on_magnetic_ballast_fl) ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [March 13, 2013, 6:56pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/11 "2013-03-13T18:56:39Z")
here is an example > **[Leviton Decora 120/277-Volt AC White Occupancy PIR Sensor R52-ODS10-IHW - The...](https://www.homedepot.com/p/Leviton-Decora-120-277-Volt-AC-White-Occupancy-PIR-Sensor-R52-ODS10-IHW/202721357?catalogId=10053&langId=-1&keyword=pir%2Bswitch&storeId=10051&N=5yc1v&R=202721357)** > > The Leviton Decora wall switch occupancy sensor is the ideal energy-saving choice to provide automatic (auto on/off and manual on/auto off) lighting control in a variety of commercial and residential applications, including offices, conference rooms,... ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [March 13, 2013, 9:51pm UTC](https://boards.straightdope.com/t/motion-sensor-for-fluorescent-lights/652823/12 "2013-03-13T21:51:07Z")
> [@Fubaya](#): > > I bet he was thinking of dimmers, they often don’t work with fluorescent lights. Many electronically-activated switches use [triacs](http://en.wikipedia.org/wiki/TRIAC) to control the load; the problem with a triac is that they need current to continuously flow in order to stay on, and are usually driven by a brief pulse to switch them on. Electronic ballasts in particular, especially if they don’t have power factor correction, only draw current in brief pulses near the peak AC voltage ([see here](http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/content/content/73569/73569_fig01.gif)), so it would only work if the triac were pulsed near the peak voltage. better designs use MOSFETs, which are held on for the entire “on” period (which may also not be the full half-cycle with a triac-based switch, although effectively close to 100% on for an incandescent) or relays.