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I bought a bunch of these motion sensor switches.

I also want to use these dimmable LED bulbs.

The motion sensors do not have a neutral wire connector. My outlets only have a live wire and it would be prohibitively expensive to put a neutral wire in.

I understand that regular LEDs flicker due to the trickle power from the sensor.

I want to know if dimmable (triac-compatible) LEDs would also flicker?

Also, if I buy the dimmable LEDs and they don't flicker am I ok to use them? Or will the trickle power damage them or shorten their life?

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  • Some questions: A) doesn't that motion sensor link say the units are discontinued? B) Your use of "neutral" and "active" to designate wires is confusing to me (though I don't live in Australia). Your outlets should have one "neutral" wire, one "live" wire (alternatively called "hot" in the US) and, ideally one protective "earth" wire (AKA "ground"). Any kind of normal (single phase) load (like a light bulb) is normally attached to the "live" and "neutral" wires.
    – RedGrittyBrick
    Aug 5, 2013 at 19:22
  • Hi, I edited to reduce confusion. Also, the switch only runs inline to the live wire. So it has a red wire coming in and a white wire leading to the light. The light then has a white wire coming in (live) and a black wire leading out (neutral). The ebay seller says it's discontinued - but only for his own store. They still sell them everywhere. Especially since you need a neutral wire for the switch and most houses don't have them as I understand.
    – skybreaker
    Aug 6, 2013 at 1:13
  • This type of device is based on a compromise. The upside is not needing neutral. The downside is they only work with incandescents (or something designed to behave in that particular way). You can also have additional LEDs in parallel but it needs one incandescent (or workalike) to function. When that bulb burns out it will stop functioning.
    – Harper - Reinstate Monica
    Mar 26, 2016 at 21:40

1 Answer 1

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Reading between the lines ...

Where I live, a normal domestic lightswitch works like this

 Fusebox                  Ceiling                   Switch
 =======                  =======           live    ======
   Live  ----------------------o------------->------o/ o-.
   Earth --------------------o--------------------       |
   Neutral ----------------o | o----------<--------------'    
                           | | |      switched live
                           |   | 
                           \/\/\
                            bulb

(At "ceiling" there is a junction box / rose where wires are joined)

Because there is no neutral in the switch backbox, there is no way to complete a circuit there and power any active component like a PIR motion detector.

Incandescent bulbs have a low resistance when cold and off butr develop a high resistance when hot and on.

You can exploit this feature to power a gadget in the light switch, instead of a simple switch you add a high resistance load across the switch, this allows a small current to pass through the incandescent lightbulb when the switch is off. This small current is not enough to light the bulb (the wire inside is not red hot, it might glow a tiny bit though, depends on current)

     Switch
     ======
         /
 ----+-o/  o--+---.
     |        |   |
     '-/\/\/\-'   |
        PIR       |
                  |
 -----------------'

However, any kind of LED lamp is not going to have the characteristics of an incandescent bulb which are being exploited here. Your PIR motion detector is unlikely to work if the lamp is not incandescent.

If it does work, it would be because the LED lamp's internal driver circuit can work from lower voltages and currents - so you are likely to see some unwanted visible effects. It might be that some manufacturers use a type of LED-driver circuit that would allow your PIR switch to work but you may have to buy a lot of different LED lights to find one that does. You might never find one that does. Without knowing the internal details of the specific LED lamp it is difficult to make any predictions.

I notice that the advert you link to has a link to a replacement part whose description says it does work with LEDs. It is reasonable to infer the vendor is aware that the discontinued one does not.

Note on terminology:

Your Q was hard for me to understand because you are using terms in a way that is non-standard (at least in my part of the world)

trickle charge - is a small current used to slowly charge a car battery.
active wire - is not a term I've seen used in relation to household power.
outlet - usually means a 3-pin wall socket (not a light switch back-box or patress)

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  • Thanks. I should probably rephrase my question to - is there any way to use the sensor I listed with LED bulbs without installing a neutral wire? some people have mentioned things like putting an incandescent light somewhere along the line, but I haven't been able to make sense of that advice. It seems to me that all I need is something inline before the LED that deals with the trickle power.
    – skybreaker
    Aug 7, 2013 at 11:12
  • @skybreaker: You could try putting either a 15W 230V pygmy incandescent bulb or a 7W 230V nightlight incandescent bulb in parallel with the LED unit (not in series with it).
    – RedGrittyBrick
    Aug 7, 2013 at 12:57
  • what would be the issue with putting it in series?
    – skybreaker
    Aug 7, 2013 at 16:47
  • 1
    @skybreaker: 1) In series it wouldn't provide a low-resistance path to neutral for the PIR. 2) In series it would drop the voltage available to the LED lamp to the point where the LED lamp might illuminate dimly or not at all.
    – RedGrittyBrick
    Aug 7, 2013 at 17:41
  • @skybreaker: the purpose of the bulb in parallel with the LED unit is to allow a SMALL flow of current to persist when the switch cuts out the high current levels. When the switch is off, it has control logic in parallel with the switch to take in enough power to keep itself operational (does not need much). An incandescent bulb lets this through (without lighting) while the LED unit cuts out.
    – Skaperen
    Oct 6, 2013 at 18:20

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