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Thread: Motion Sensor and compact fluorescent bulbs

  1. #1
    DIY Member paulsiu's Avatar
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    Default Motion Sensor and compact fluorescent bulbs

    The light on my ceiling light burnt out, so I replaced it with a compact flourescent. Much to my surprise, it did not work as I expected. The light is hooked up to a motion sensor and when the bulb doesn't turn off. It instead glows dimly or strobes.

    Is there a incompatibility issue with montion sensor and compact flourscent? Why is that?

    Since the bulb is glowing dimly, this means a low current is going through the bulb. Does this mean motion sensor actually draws power and so isn't so energy efficient after all?

    Paul

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    Plumber jimbo's Avatar
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    For a general rule, compact fluorescent bulbs are NOT compatible with motion sensors or dimmers.

    There are exceptions for dimming: you must get a bulb AND ballast AND dimmer which are ALL rated for dimming. The bulbs will more expensive, and the dimmer will run over $50.

    Many simple motion sensors like you probalby have work by "stealing" a tiny amount of current when the bulb is off. An incandescent bulb pretty much ignores this. Flourescents tend to glow or flicker. You can get a compatible motion sensor....it will set you back about $50.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by paulsiu View Post
    Since the bulb is glowing dimly, this means a low current is going through the bulb. Does this mean motion sensor actually draws power ...
    Sure, and lighted switches do the same ...

    Quote Originally Posted by paulsiu View Post
    ... and so isn't so energy efficient after all.
    Sensors and lighted switches are tools that can *facilitate* efficiency, and they do that as efficiently as possible by consuming a minimum amount of energy necessary. An exception, I believe, would be an "energy-free" sensor for a night light, but even that kind of sensor needs energy from the sun (or from some other source) to hold the circuit open and keep the light off until darkness again takes over.

  4. #4

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    Of course it draws power - so does anything that is actively monitoring for an event to happen. Your smoke detectors constantly draw power looking for smoke, your tv constantly draws power looking for the remote, your garage door opener, your furnace.... They draw only a small fraction of what they do when they are on, but they still draw power. I think standby losses account for something like 7-10 percent of all power consumed in the average home. Yes you will save more $$ by not using a motion sensor and never turning on the light. However if you want the light on for just 5 minutes when you get home at night the motion sensor will save you $$$ over leaving the lights on all day or using a timer.

    The reason the CFL won't work is that the motion sensor you have uses the filament in the bulb as a wire to pass a small amount of current for the motion sensor. The bulb does not light because the amount of current drawn is small and the filament does not heat up enough to generate light. When you replace a standard bulb, which is essentially a resistor with a CFL, which is essentially an electronic circuit, either the motion sensor or the bulb or both will fail to work properly. This is because the electronics in the CFL will not pass current in a predictable way, thus causing the results you see.

    They do make motion sensors that work with CFLs, but why bother. The motion sensor turns on the light the minute you need it and CFLs take another minute to warm up to full brightness. By then you probably don't need the light any more. Also CFLs don't like to be repeatedly turned on for short durations. This reduces their life. They want to be on for at least 20 minutes at a time on average.

    -rick

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    DIY Member paulsiu's Avatar
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    Thank you everyone for the explanation. I knew it would be something simple, but there are few explanation when I google.

  6. #6

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    Well, I just rigged a CFL-approved (by their package anyway) motion sensor to a closet light with a CFL bulb and am also getting the glow described above. Initially the bulb was flickering lightly but that stopped. It also is not as bright in auto on mode as in manual on mode. The QUESTION is, does a CFL-rated dimmer or motion sensor also require dimmable bulbs? The second question is why is this all so damn mysterious? Why can't it all be spelled out clearly so we know what the hell to buy? For example: LED bulbs. One guy tells me they're not dimmable. Another says you need CFL-rated switches. Another says no, any dimmer or switch. It CAN'T be that complicated.

    As for the comment about it needing to warm up longer than the time needed for the light... In this case I don't see that as an issue. CFL flood lights I just installed in the kitchen do take 30 seconds to warm up, but this bulb doesn't seem to need any real time to get to full bright (except as mentioned that it is slightly dimmer in auto on mode than manual). PS- the reason for motion sensors is because my wife loves turning on lights but hates turning them off! So I'm putting one in the master bedroom closet (where the idiot electrician put the switch IN the closet), the laundry room and the garage, all places where the switches are in the room so I can't insall switches with monitors to know from outside the affected room that a light was left on. A slight penalty in brightness in any of those rooms means little. I WOULD, however, prefer to use CFLs on principle if nothing else.
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    Plumber jimbo's Avatar
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    It is a minefield. Generally, a motion sensor or dusk-to-dawn sensor needs to be a 3 wire device, not a two wire. Besides that, you do need to read the manufacturers specs carefully. Some devices will be compatible with magnetic ballasts, but NOT electronic ballast. Integrated CFL are generally an electronic ballast.

    LED is a whole new ball game. Many of those need special power modules and special dimming controls. At home, I have opted for SWITCHES. I turn the lights on, and turn them off. If I need more light, I turn on ANOTHER one!

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    General Engineering Contractor ballvalve's Avatar
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    I have had a long run of many cfl's on a yard for years. I use the 3 wire sensor from a standard 10$ outdoor motion sensor, and not a drop of glow for me! Its strictly on and off.

  9. #9
    DIY Junior Member tmleacock's Avatar
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    Default Motion Sensor and compact fluorescent bulbs - a solution

    I found that if you are replacing a switch with a motion sensor and want to use CFLs, often you don't have the option of a 3 wire connection (the switch you are replacing only has two wires running to it). However, my circumstance was such that I needed to control a bank of lights with one motion sensor, not just a single bulb.

    So the solution for me was simple. Use all CFLs in the circuit but include just one incandescent bulb so that the motion switch has the trickle current it needs to operate properly.

    Hope this helps anyone trying to control more than one bulb with a motion sensor, wanting it to work, and wanting to use as many CFLs as possible, while at the same time constrained by only 2 wires available in the wall switch box.

  10. #10
    General Engineering Contractor ballvalve's Avatar
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    Why do mine work fine with the cheapest motion detector made?

  11. #11
    DIY Junior Member All_Thumbs_Handyman's Avatar
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    Default 2-Wire Dawn-to-Dusk and Motion Senson in Same Circuit

    Have read the various replies to this thread and I'll chip in my 2 cents worth in the hope it helps someone with a similar problem.

    I have a single 2-wire circuit servicing both the front porch and the lights outside the garage, which is around the corner of the house. I wanted to improve nighttime security and not spend a bundle on electricity.

    The front porch light is first in the run after the switch - I replaced this with a fixture having a built in dawn-to-dusk sensor and put a low Wattage CFL bulb in it.

    I replaced the lights outside the garage with a fixture that has both built-in dawn-to-dusk and motion sensors - after dark the motion sensor becomes activated. These lights only function properly with an incandescent bulb and here I chose to use 100W bulbs because I want maximum illumination and can set the length of time the bulb will remain on to 1, 5 or 10 minutes thereby limiting energy consumption.

    This set up works well my porch is always illuminated when it is dark using a CFL that draws 15W and if anyone approaches the driveway the 100W bulbs are set to come on for 5 minutes. When not in use there is indeed a faint glow to from the incandescent bulbs.

    The light fixtures used were not expensive and this set up satisfies both the need for security and low energy consumption.

  12. #12
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by ballvalve View Post
    Why do mine work fine with the cheapest motion detector made?
    Some motion detectors have a relay controlling the light.

    If yours has a relay, You will normally hear the relay click when motion is detected and the light comes on.
    Theory only works perfect in a vacuum.

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