we have an issue were our downlights have a dim glow when switched off.

electrician has been back to replace downlights but no success. glow doesnt happen every night, often a big gap in between glowing. tested the wiring and shows anywhere up to 3 volts through the active wire when switched off.

is it normal to have up to 3 volts running through the active wire? and is this enough to cause an LED downlight to glow.


  • Was the hot feed run to the switch first, or to a light first? Is the switch a regular wall switch, or something with fancy "smart" functions? – ThreePhaseEel May 2 '19 at 23:49
  • the switches are the clipsal iconic range. just used as normal switches but i believe some smart functions can be added. to be honest i dont know if the feed is to the switch first or the light first. – Deelicious May 2 '19 at 23:59
  • I always question when things like "Electrician was called out and replaced the lights" are said. There's no way the lights could possibly be at fault here, and any electrician should know that or they shouldn't have the job. No electricity = no light. If there is a glow, there is electricity, so it has to be a switch or similar issue. – JPhi1618 May 3 '19 at 14:50

"Smart" switches use solid state (electronic) switching devices called "triacs" in most cases. The problem with triacs is that they don't completely turn "off" because the solid state nature of them has a very tiny amount of "leakage current" through them. When used on incandescent or even CFL lamps, that leakage current is irrelevant because the circuit can't really do anything with it. But LEDs take so little energy to illuminate that this tiny amount of leakage is enough to keep them glowing a little bit. The only way to stop it is to have a hard "contact type" switch that makes an air gap to isolate the LEDs off line. But those are typically not your "smart" switches. I have heard people say they can add one incandescent lamp to a fixture and that problem goes away, but I've tried it and it causes other problems if you try dimming.

  • The smart switch might be a two-wire device, deriving its electrical power by being in series with the lamps. As @JRaefield states, that's enough to keep the lamps on. One light in my house requires two 7-watt lamps in series (3.5 W load) across the load to work with a two-wire "sound switch". – DrMoishe Pippik May 3 '19 at 1:37
  • 1
    triac leakage current is typically only a few hundred micro amps, which a bleeder resistor should swallow up most of. I've not seen off+dim from a triac controller, each time it was from a non-neutral-using active switch (like a dusk-to-dawn or motion) or from parasitic inductance (removing switch doesn't stop dim+off). – dandavis May 3 '19 at 21:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.