Q&A: LED bulbs and radio buzz

I recently bought four LED lights to replace CFLs in the kitchen. I’m very happy with the light output and colour, but unfortunately there is one side effect—when they are turned on they make my clock radio in the bedroom buzz. What is this caused by and is there anything I can do to stop it? I would just put these globes in a spot where I don’t need to use them in the morning, except that they are the only screw fittings in the house. Another LED in the pantry has no effect.

This is a common problem: many LED bulbs produce electrical noise as they have switchmode drivers inside them to convert the power supply voltage down to whatever voltage and current is needed for the LEDs. The electrical noise can be radiated as radio waves from the house wiring, causing interference, or it can travel back through the wiring as electrical noise, causing the same problem. I suspect your problem is the former.

There are a number of solutions, of which several are quite simple. The first is to get some clip-on ferrite beads, these are the sort of thing you see at the end of some computer leads, basically a lump in the cable, but in clip-on form rather than moulded in. Examples can be seen at www.bit.ly/ferrite1 and www.bit.ly/ferrite2. You simply clip them over the cable as close to the light fitting as possible.

If that doesn’t fix it entirely, using a larger ferrite and winding two or three turns of the cable through it will increase the effectiveness of the ferrite.

You can also put small value capacitors directly across the socket, but this involves electrical wiring, so you’ll need to find an electrician experienced at mains wiring, and you must also use the correct capacitors (X2 types of appropriate voltage rating). A simpler and more electrician friendly option would be to have mains filters connected at the fittings. A typical example of a suitable unit (which could be fitted inside a junction box) is Jaycar Electronics part number MS4001.

But definitely start with the clip-on ferrites, they are simple to install and no electrician needed, assuming the wiring is accessible from inside the ceiling. Just be careful if installing them that you ensure the wiring is in good condition – old wiring can have degraded insulation and be very dangerous. If in doubt, contact an electrician.
Lance Turner

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