/ Home & Energy, Technology

The energy-saving LED bulb that switched off the radio

An LED bulb lighting up the darkness

We get sent some weird and wonderful tales of products going wrong, but one story piqued our interest so much that we just had to send it to the lab to test it out. Can you help us shed more light on the mystery?

Last year we received this intriguing message:

‘I recently changed six halogen down-lighters to more energy efficient LED bulbs. Unfortunately when the lights were switched on, the DAB signal on my radio was wiped out!’

To try and figure out this conundrum, we sent a batch of cheap, generic 12V LED bulbs to our lab and found that when a digital radio was placed within a few metres of the switched-on bulbs the signal went fuzzy. When the radio was placed within a few centimetres of the LED bulbs, it cut out all together.

The plot thickens

LEDs are ultra energy efficient light bulbs that can last up to twenty years and have been hailed as the future of home lighting.

It seems our members are not the only ones who have had this problem. There are other accounts of LED bulbs affecting radios, with AVForums also collecting stories. Nick Tooley shared his experience:

‘I had the same problems with LED bulbs wiping out DAB reception and tried several types of bulbs, but to no avail.’

And it seems that the issue may not just be limited to digital radios – TVs may also be affected. After fitting LED down-lighters in his kitchen, Jackord noticed the following problem:

‘While the lights are much better, we then by accident noticed that the digital TV would not work (I was complaining that we had no reception at all, did not make any sense, began to think that there had been some sort of catastrophic disaster which stopped the TV stations from broadcasting…lol) then someone turned off the ceiling lights in the kitchen and, hey presto, on came the TV.’

Shedding light on cheap bulbs

So what bulbs are affected? We tested three 12V generic LED bulbs and we also compared them to branded 240V GU10 LEDs and some halogens. We found only a very minor interference with our radio signal. So at this stage, the issue seems to be limited to cheap knock-offs rather than branded goods.

We’ve only done preliminary tests on this problem, so can’t make any concrete conclusions on why this is happening or how widespread this bizarre problem is.

That’s where you come in. We need your help – have you had this problem? If so, please enlighten us in the comments below, including what model bulb you were using and where you bought it.


Here is a Youtube clip of my problem shot four years ago.

The portable is on FM despite saying DAB on the front, and the ReVox tuner is fed from a four element roof mounted FM aerial. I realise the ReVox is out of the ark, but that model was once used by a HiFi magazine as the bench mark against which all others were tested. I suspect that there is little or no chance of improvement so DAB it is!

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Thanks Motco. That’s good evidence of severe interference. 🙁

It would be interesting to know whether the tuner picks up interference with the outside aerial disconnected because it is possible that the tuner circuitry rather than the aerial may be picking up interference due to lack of screening.

You might be interested in the Convos about the forthcoming switch-off of FM radio, this one being the most recent: https://conversation.which.co.uk/technology/fm-dab-radio-switch/ Even early DAB sets could become useless with the migration to DAB+, although the BBC has shown no sign of doing this.

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Sorry for being a heretic but I have seen problems with lack of screening in expensive hi-fi equipment. The circuitry of my Hacker RP38A portable radio (definitely not hi-fi but quite expensive in its day) picked up interference from TVs and CB radio much better than cheaper radios. 🙁

I think Motco has an A76 Mk II tuner, which should go on for a few years yet.

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I made the point that it’s not hi-fi, but I have seen interference pick-up by hi-fi separates. If Motco unplugs the aerial we can find out whether the interference is coming in via the aerial or the circuitry.

Of course interference would not be a problem if LED lighting complied with the relevant standard.

Duncan, the problem is easiest to describe by likening the noise to the hiss that is heard on cheap FM tuners on stereo reception (but not on mono) especially with weak signals. The sound is hiss-free until the LED lights are switched on and then a very obtrusive noise starts.

It is an A76 tuner and I also have a B795 linear tracking turntable, and an A77 four track open reel machine. I was quite keen on sound quality before my ears aged along with several other faculties! The tuner is not quite perfect at the moment; the stereo decoder is not operating. I have a service manual but have not yet got around to ploughing through the diagnostics. I suspect the old electrolytic capacitor(s) may well be to blame. My enthusiasm for HiFi equipment is now much reduced so I have not spent money on equipment since I realised my hearing stops at about 10kHz (I estimate) and is certainly not improving. A DAB tuner provides a sound quality good enough.

Duncan has not been seen here recently.

I think you have been unlucky with your choice of LEDs. If they were simple bulb replacements it would be very easy to replace them with ones that don’t cause interference. The simplest variety use a capacitor feeding a string of LEDs, which is crude, has a lousy power factor but does not cause interference. High frequency switching drivers using inductors are more efficient but can cause interference if poorly designed. It’s usually DAB rather than FM interference that is the problem.

LED panels are more of a challenge, but if you took a portable radio to a lighting shop with a display you might be able to find a solution.

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In Duncan’s absence, a little clarification on FM stereo noise, and a practical suggestion.

The hiss on stereo and not on mono is characteristic of weak signal to the tuner. Stereo FM has a signal to noise four times worse than mono so requires four times stronger signal to be as noise free as the equivalent mono. I thus deduce that the LEDs are getting in either at the aerial or at least in circuits before the quadrature detector/stereo separator.

The LEDs or more likely the wiring to them could be broadcasting FM increasing the noise at source/diminishing the signal. If your mains wiring extends to the roof area near the antenna, then it is entirely possible that the high frequency goes all the way up there too. If you can get to the power wire to the lighting unit, try clipping a ferrite ring around it – as near to the light as you can reasonably get, Amazon actually do a range quite cheaply – search out “ferrite clip-on”. This will at least substantially reduce any copper-born radiation.

That’s a thought, Roger. Round here it is common for TV aerials to have masthead amplifiers, fed by a mains power supply. If Motco’s roof-mounted FM aerial is near a TV masthead amplifier it could pick up interference.

Sorry Duncan, I had not seen you post recently.

Agreed, Wave – and cheap mast head amps could be more susceptible – so likely worth a bead at that end too.

I have got a near-masthead amp wavechange (in the loft) but it is a long way from the FM aerial.

Oh well, best of luck with the ferrite sleeves.

Duncan, I admit that I am only an occasional visitor to these forums (fora?) but I am truly grateful for your interest and amazed at your in-depth knowledge of what was only ever a minority market product, and is now verging on antiquity! I should give more attention to the tuner especially as it seems likely that FM transmissions could be switched off in the medium term. You have aroused my interest again and I shall look at my service manual for values and locations and acquire a selection of components so as not to have a dismantled unit lying around while they are sourced. I also have a pair of ReVox (re-badged Beyer actually) headphones but the polyurethane ear-pads decay by hydrolysis into crumbs of dry dust. Replacements are available at ridiculous cost despite the brand more or less disappearing back into Studer, but like you, I rely on hearing aids these days and they are not really compatible with cans. Mine are NHS ‘finest’ Oticon digital aids set up by a delightful Polish lady named Agnieszka at Wycombe Hospital after an extensive audio survey of my hearing. You are right when you say that the range of frequencies that they enhance is far wider than my hearing has had for many a year. In fact it is like having my own in-built graphic equaliser in my ears! The idea that aids amplify is inaccurate – in my case anyway, they actually emphasise the regions of the audio spectrum that the patient has lost.

The turntable, like the tape deck, was remaindered stock so didn’t cost full retail price or I wouldn’t have either of them. A Sony shop in High Wycombe had the turntable in its window for some weeks before I decided it had reduced as far as it would ever do, and the deck was heavily discounted by a Tottenham Court Road HiFi shop when the B77 was launched. Nevertheless I suspect that if I totted up the cost over the years it might well exceed the figure you suggest. Fortunately I was quite well paid at the time – penury came later!
Thank you for your valuable help, I enjoy indulging in a forum that is not testosterone fuelled anger like one of the motoring forums I visit to feed my horsepower addiction. Too late I’m sure but may I wish you a belated Happy Christmas, and hopefully a timely Happy New Year.

Here’s a small Christmas present, Motco – a service manual with circuit diagrams for the A76: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&ved=2ahUKEwjp-9fZvs_mAhUVM8AKHevUA74QFjALegQIAhAC&url=https%3A%2F%2Fwww.vintageshifi.com%2Frepertoire-pdf%2Fpdf%2Ftelecharge.php%3Fpdf%3DRevox-A-76-Service-Manual.pdf&usg=AOvVaw2_M96KSXyTD93e_yIXu9BR

Back in the 70s it was common to supply manuals with Hi-Fi equipment or provide customers with them on request. Happy days.

Thanks wavechange! I have got a printed copy – somewhere… The downloaded one you kindly linked me to will save me disrupting the whole house looking for the paper copy!

Light bulbs emit radio waves, as not all the electricity is converted into visible light (radio waves and visible light are simply different levels of the same electromagnetic energy).

That said, problems with radio inference only occur with some but not all LED lamps. No other lamp types seem to suffer this problem. It follows that the most likely cause of the problem is cheap and nasty driver circuits, as opposed to the actual light emitting diodes themselves.

That is right Derek. However some self-ballasted compact fluorescent lamps also caused interference.

Radio interference from CFL (compact fluorescent lamps) was known before LED lamps arrived but was not a common problem. There were fewer manufacturers and presumably they took more notice of the regulations to limit the amount of radio interference emitted by products.

It’s difficult to know if a LED lamp has a cheap & nasty driver, as Derek puts it.