I'm debugging an issue with flickering lights in a house with older wiring (1950s, braided sheath, two wire, no grounding).

I have a lamp with a solid state switch (touch lamp) and LED bulb inserted. I also have a white noise machine plugged in to the same 2-prong outlet. Flipping the the rocker switch on the white noise machine creates a momentary flash of light on the LED bulb when the lamp is off.

I called an electrician and he said it was likely just the LED bulb being sensitive.

I believe I'm okay from a safety perspective:

  1. another lamp with a cradle switch does not flicker (i.e. there is no arcing, and only lights with solid state switches are leaking current)
  2. nothing is warm to the touch and there are no smells.

But I'm curious and confused why this is happening. It does not happen in the part of my house with newer wiring. I took an oscilloscope to the outlet and see momentary voltage spikes up to 50V on the neutral wire when toggling the white noise machine. When I hooked up the lamp to the neutral from a different circuit it does not flicker (though I forgot to test the case where Hot is on the other circuit and Neutral is on the suspect circuit).

What is going on here? Is this due to lack of grounding in the outlets? Is this high impedance in the wiring?

  • What happens to the white noise machine when you turn the light on/off?
    – FreeMan
    Sep 15 at 14:47
  • nothing, but it's spinning mechanical noise maker so brief interruptions in power are likely not detectable. We had to take the LED lights out of our overhead fans because they would flicker on throughout the night in a similar fashion (they also have solid state switches internally controlling the light).
    – jdizzle
    Sep 15 at 15:31
  • 1
    Is the touch lamp designed and rated for LED "bulbs"? When the neutral wire surges voltage upward, does the hot also surge downward? I assume you are using ground as a reference. Any surge suppressors in the area? Sep 15 at 17:04
  • 1
    Use caution measuring line voltage with a scope, i have seen the front end blown out without an isolation transformer. The voltage bump from the white noise generator is probably enough to cause the flash you probably would not see anything with an incandescent lamp. The input for touch lamps are usually capacitive I am surprised that if it flashes it doesn’t stay on so it may be the spike it self generating enough potential on the cathode to cause the flash.
    – Ed Beal
    Sep 16 at 1:04
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    I swapped the LED bulb in the touch lamp with an incandescent bulb. It still flashes, though it's very dim. The white noise machine says it takes 18 Watts. We have multiple of these devices and have never had any sort of issue like this until we moved in this house with older wiring (we recently moved, and this is the identical setup to the old room which had no issue). Is it possible this is an issue with a poorly connected neutral on this circuit?
    – jdizzle
    Sep 16 at 2:15

Sounds like a faulty touch switch. Is the lamp properly grounded? You may consider putting a dimmable LED bulb in as the driver is made to handle voltage variations. You may still get flickering but shouldn't be a safety issue.

You also may consider replacing the lamp.

  • Lamp is only two wire, so no grounding. The reason it’s odd is because it never happened before and we’ve had other flickering issues since moving in.
    – jdizzle
    Sep 19 at 11:32
  • Their usual metal bases aren't they? Might be time to get a new lamp. 😱
    – DrSparks
    Sep 19 at 20:48

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