/ 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.


I have three ‘corncob’ mains-fed LED lamps in conventional fittings in a bathroom and they are cold white, none too bright, and they cause a strobing effect. If you watch the water from the shower at night you can see the individual water droplets and if you make a sweep motion with a splayed hand across your feild of vision the hand/fingers appear to be moving in a jerky fashion. I suspect that the mains is processed by some sort of half-wave circuit and the lack of thermal inertia in the light source (compared with a thermal filament) accentuates this ‘flicker’. We sacrifice smoothness of DC supply for cost and efficiency it seems.

Well yes Motco as far as direct DC supplies are concerned this was mooted on several industrial engineering websites even to the point of mains derived DC.
Most of the cheaper and usual supply of LED bulbs are SMPS fed from miniaturized circuits in the base of the bulb . Philips among others sell non SMPS bulbs and even series/parallel connected multi LED versions direct from the mains using a ful;l wave diode network including smoothing .
Even better LM317 regulators are used but they are in the stuff sold to industry not the public and Philips has an online guarantee to businesses that they guarantee them for 3 years no quibble return if they dont last ,shows you the difference between business and public .
They also sell element types of LED bulbs and direct AC LED,s no DC conversion .
none of them produce RF radiation .
Radio “Hams ” round the world are very angry over this as calls to stop it are met with deaf ears and complain loudly when on car mobile and approach LED traffic lights especially worse when they strobe .
I know the strobe effect you talk about after I got both eye lenses replaced in the dark looking at an red LED and moving my head I got bad strobing -multiple LED,s in my vision its died down a lot now.
Good to have more people like yourself with technical knowledge here.

For those like yourself and Wavechange here is a top class well known worldwide Electrical Engineers ( Professionals ) website with the same comment and reply –

This effect is not seen with most LEDs because the driver operates at too high a frequency and the phosphor used to produce white light from blue LEDs helps provide a smoother light output. The strobing effect will be seen if they operate at 50Hz with half-wave rectification or 100Hz with full-wave rectification. Some ‘corncob’ LED lamps have been reported to be unsafe because of exposed live parts. Despite the strobing effect and lower efficiency, I don’t think you will have problems with radio interference.

Some LED rear lights used in cars obviously operate at low frequency because strobing can be seen if you wave your hand in front of them. I’ve seen the strobing effect with traffic lights but I don’t think they all do this.

Yes, Wavechange, I first noticed the strobing effect when driving on a motorway at night back in the late 1990s or early 2000s. Because an alert driver is constantly scanning between mirrors and the road scene, transverse movements across the field of view inevitably cause tail lights to pass rapidly across the field (relatively), and seeing multiple images from up-market cars (in those days) was almost alarming. The reds from leds seem to have a higher blue content than incandescent lamps, and those cars like my (now ancient) BMW Z3 that have an LED high level centre brake light and filament main brake lights give the illusion of separate circuits for each. This is because the LED goes from OFF to full ON instantly to the human eye, and the filament has a perceptible ‘rise-time’ and decay that they almost appear independent.
I wonder whether those people who dislike fluorescent lighting now find LED office lights yet more headache inducing than even their hated strip lights?

I’m convinced that some of us are more affected by flickering than others, Motco. Peripheral vision is most affected. In the days when CRT monitors were standard I could look into a room and spot the one at the default refresh rate of 50Hz. Most people did not see this but I was not alone. I was also aware when fluorescent tubes with a choke ballast were nearing failure, when they stop emitting as much light on one half cycle. I’m unaffected by LED lighting running at high frequency. A portable radio on the LW band held next to a LED bulb will show if it’s operating at high frequency.

Wavechange – many years ago I bought a miniature wide-band RF tracer from Maplin I mentioned it here years ago.
It covers LF right up to 2Ghz , it cost me £15 , on checking for tracers nowadays most of the ones for sale at a reasonable price are in the USA -one cheap one in the USA was $20 -here it was £70 but if you think that is bad I found the exact -identical one to mine for sale in the UK with just a name change-same size same internals price -are you ready for this ?? —–ONE HUNDRED and SIXTY POUNDS– wow !
Dont tell me this country isn’t “r****** off customers royally that’s just pure greed .

It can be used for tracing LED RF leakage .

I am seeing more examples of overpriced products on sale. Even out of print books are sometimes offered at ridiculous prices, and I’m referring to ones that are fairly readily available rather than rare ones.

It would be interesting if you can find any significant differences between emissions from different brands of LED bulbs, Duncan.

The problem is I have only two LED bulbs in the house and neither of them produce large amounts of RF . My local council gave them away free at the time ,they are very big and old fashioned .

I had a look at one used as a bedside light its a Philips -master -square plastic base thats hot but they go on forever even when left on 24/7 no instability etc.
Four individual tubes grouped together ,going by the label they look like they were made by Philips in Europe as opposed to “manufactured out ” elsewhere Wavechange.

It might be worth looking at the newer ones. I have a house full of LED lamps now and don’t have problems with radio interference, and yes they were made in China, including the ones branded Philips. The one that did cause a slight problem was made in a European country.

Back on topic, I have just replaced my old Denon kitchen mini-system in which the DAB function had died, with a Panasonic similar. The FM (stereo) reception is still hissy when the lights are on, but on DAB it works perfectly even on a randomly tossed wire aerial.

Being unable to listen to your favourite radio station due to interference is bad enough but I had not appreciated that it could be a safety issue. In another Convo, Duncan mentioned that the US Coast Guard had issued a safety alert about the danger of LED lighting interfering with marine band VHF radio: https://www.dco.uscg.mil/Portals/9/DCO%20Documents/5p/CG-5PC/INV/Alerts/1318.pdf?ver=2018-08-16-091109-630.

Wavechange , I am at present unable to find the original document from Germany on testing of various brands of LED light bulbs but I think the Elektor magazine has the report but– while I joined up with them to access the report they require me to upgrade from “free ” to becoming a “paid for ” member .

The German organisation –DARC is providing Elektor with data -Deutscher Amateur-Radio-Club .
Other LED problems include lights on towers that aircraft cannot see (with night goggles ) see-
I will keep trying to obtain the original test document .

From memory it displayed images from wide-band spectrum analysers and graphs as well as a list of makes of led bulbs tested .

I can now access Which ? with Waterfox some “bot ” slyly turned OFF javascript for Which ? while leaving most other websites “okay ” — it took a while to find it and turn it back on.

I hope that real safety issues are systematically investigated and resolved. Thinking back, I remembered earlier mention of potential safety issues being mentioned by amateur radio groups. Here is a page that mentions this Convo: https://www.ukqrm.org.uk/lighting.php

DerekP says:
26 January 2019

Ultimately, I guess international standards bodies will have to play their part in reducing the impact of LED lamps on matters such as maritime and aviation safety.

The standards are there and what is lacking is independent testing to ensure that products comply.

DerekP says:
26 January 2019

wavechange – are you saying that some manufacturers and retailers are telling lies about compliance with applicable standards?

I’m not making any such claims, Derek. From posts in Which? Convos and elsewhere, there is evidence of a problem and some amateur radio enthusiasts have investigated the problems in some depth. I suspect that the problem is because brand owners do not always test compliance with standards when they buy from other manufacturers.

Measuring radio-frequency interference requires specialist equipment and perhaps one of the easiest examples of non-compliance is the lack of adequate isolation between mains voltage and low voltage circuitry in many phone chargers etc. There are YouTube videos that give examples of this problem.

In the UK -EN-55015-2006 Standards apply , I cannot post the URL for the website as its not HTTPS but I will post some of the wording-

Interna­tional stan­dard EN 55015:2006 is applicable to:

all light­ing equip­ment intended to be used for light gen­eration and illumination purposes and intended to be used with batteries or connected to low voltage mains network;
lightning part of installation or multifunctional equipment if one of the main purposes of usage is illumination;
accessories that are usable only with lightning equipment;
IR and UV radi­a­tion equipment;
scoreboards, advertising signs;
lighting equipment intended to be used outdoors;
lighting equipment intended to be used in busses and trains;

International standard EN 55015:2006 have no classification of equipment it covers.
Insertion loss requirements must be met in frequency range 150kHz-1.605MHz (limited applicability).
Conducted emission requirements for mains ports must be met in frequency range 9kHz-‹30MHz.
Conducted emission requirements for load terminals and control terminals must be met in frequency range 150kHz-‹30MHz.
Radiated emission requirements must be met in frequency rage 9kHz-‹300MHz.

Various radio websites who arent friends with led lights but have all the technical equipment to show RF interference all agree Dimmable led lights are the worst culprits.
My own view on this is the action of the SMPS circuits which have interference suppressants which only cover non sinusoidal waveforms of a set frequency range but dimmer circuits change the angle again so that you have two variants to deal with not one thereby increasing the output and frequency range beyond the scope of the suppression components .

Would it be this site, Duncan? If using some browsers you will have to apply an advanced security exception to see the site.

Hopefully the relevant authorities will deal with safety related radio frequency emissions problems and building products to a price is less of a driver than with household products.

The reason that household LED lamps contain electronic components and operate at high frequency is that this is more efficient than using passive components such as resistors or capacitors as droppers, even though the latter would not cause interference. Having a house equipped with LED lamps and no problem with radio interference, I know that radio interference need not be a problem.

Thanks for the information about the relevant standard.

Yes Ian Waterfox blocked it as “improperly configured ” -meaning its possible its been modified by a hacker but I got the URL as HTTP on Yandex.

Quite a few browsers are now simply throwing these warnings and prohibitions at anything that isn’t https, sadly.

Your right I usually click on technical websites and I cant understand why some of them are being blocked as they are far from being popular so hackers wont waste time software programming them .
I can only come to the conclusion its to limit “information retrieval ” ?

DerekP says:
26 January 2019

I believe the main purpose of https is to prevent “man-in-the-middle” attacks.


Correct Derek , as a matter of interest what if I told you that Which? pays a certain German search engine a few pence every time somebody clicks on Which?-Conversations –and I can prove it ?

DerekP says:
26 January 2019

I now have 3 Morrisons’ “pound shop” GU10 400 lumens LED lamps installed in my bathroom.

I am pleased to report that they aren’t interfering with my analogue FM radio.

Interference mainly affects DAB radio, though I have a lamp that affects FM but not DAB. My impression is that problems with radio interference are less common than with early LED lamps.

DerekP says:
26 January 2019

Thankfully, I have no need for DAB radio.

Here is a company that supplies test results on LED lights for manufacturers with digital spectrum analyser displays in real time .
Please note the graph measurements at the LHS are MINUS DB and that in DB terms the lower the minus DB the HIGHER the interference .
Please note the frequency range – 30Mhz-300Mhz and that some bulbs go higher in interference than the top frequency stop ,also note the harmonics.-
Still looking for the big report.

If you know German Wavechange here is DARC but its a different gathering of info -many pdf,s –

An open view of two led lights –

DerekP says:
27 January 2019

Duncan – thanks, some interesting stuff there.

PS – on the black graphs the units are dBm (power values relative to 1mW) and the values displayed are negative, but values higher up the graph still seem to represent greater noise. E.g a value of -60 dBm indicates more noise than the lower value of -80 dBm.

Derek-yes it does seem confusing /not logical that a lower number indicates a higher noise level but if you think when you buy a good quality hi-fi amplifier when you look at the spec. you will see –
THD = 0.001% which is minus 100DB –the combined noise and distortion is at a minute level .
Normally the public are used to positive noise levels – IE- plus 80 DB for an airplane /road drill etc .-
dB Power ratio Amplitude ratio
100  10000000000 100000
90 1000000000 31623
80 100000000 10000
70 10000000 3162
60 1000000 1000
50 100000 316 .2
40 10000 100
30 1000 31 .62
20 100 10
10 10 3 .162
6 3 .981 ≈ 4 1 .995 ≈ 2
3 1 .995 ≈ 2 1 .413 ≈ √2
1 1 .259 1 .122
0 1 1
−1 0 .794 0 .891
−3 0 .501 ≈ ​1⁄2 0 .708 ≈ √​1⁄2
−6 0 .251 ≈ ​1⁄4 0 .501 ≈ ​1⁄2
−10 0 .1 0 .3162
−20 0 .01 0 .1
−30 0 .001 0 .03162
−40 0 .0001 0 .01
−50 0 .00001 0 .003162
−60 0 .000001 0 .001
−70 0 .0000001 0 .0003162
−80 0 .00000001 0 .0001
−90 0 .000000001 0 .00003162
−100 0 .0000000001 0 .00001

Note- figures expressed in power ratio/amplitude ratio –NOT percentage.

Thanks for the links, Duncan. dBm is explained on Wikipedia, with examples of positive and negative values: https://en.wikipedia.org/wiki/DBm

As can be seen from the article showing dismantled lamps, LEDs can either use passive components or contain electronic components and inductors as drivers. The latter system is more efficient in converting power to light but can generate RF interference. The one GU10 lamp that I attempted to dismantle had the components embedded in some potting compound and I could not establish anything about the circuit design.

I don’t read German. 🙁 DARC is the Deutscher Amateur Radio Club and it’s necessary to be registered to access all the information on their website. We can at least see that some lamps pass and others fail a test.

Many people are using LED lighting and still able to listen to their radios, but the best advice still seems to be to test a single example of a lamp before buying lots of them.

DerekP says:
27 January 2019

Duncan, I think it is quite simple arithmetic to say that -80 is a lower number than -60.

For example, believing that I have £50 in my bank, I write a guaranteed cheque for £20.

To my horror, I discover that I’m already overdrawn by £60, so when my cheque is paid, my balance reduces from £ -60 to £ -80.

Back on topic, if switching on an LED lamp increases the ambient r.f. power at some frequency from -80 dBm to -60 dBm, that is an increase of +20 dBm or a one hundred fold increase – and could readily “jam” the reception of any lower powered signals there.

Your right Derek I could have put it simpler , its a built in “fault ” in my brain you are not the first to say that.

Your right about “jamming ” a hand held vhf transmitter receiver of a couple of watts can cause the same trouble to local radio reception.
Yes audio circles use – 20 -40 -60-80 -100 DB when designing audio equipment.

I’ve just bought 3 240v LED ‘Candle’ bulbs, 5.5W 470 Lumens made by GE. They interfere with my hearing aids and give me a constant buzzing in my ears. Is this avoidable?

It’s worth experimenting with different LED bulbs, Robert. You or your neighbours may have other types that don’t cause a problem. Best of luck.

LED bulbs come in dimmable and non-dimmable types. Sometimes these are clearly marked on the bulb but not always, as is the case with the 1521 lumen Philips bulb I found in the bulb drawer. That’s annoying when the lower powered lamps of the same style are dimmable.

It’s necessary to use a dimmer designed for LED bulbs because one designed for old incandescent bulbs including halogen ones may result in the LED not dimming, flickering or possibly failing.

Looking at the rating in watts with the lumen output, non-dimmable bulbs tend to be more efficient in lumens per watt. I have also noticed that 1500+ lumen lamps, which are supposed to be equivalent to 100W incandescent bulbs are rarely dimmable, and guess that the less efficient circuitry produces too much heat.

If the circuitry in dimmable and non-dimmable LED bulbs is different, I wonder if this affects radio frequency interference.

The circuits are different Wavechange I think I posted on this a short while back .
I also said the interference was working on 2 levels –
one , the fundamental + the harmonics of the SMPS which does not produce perfect DC =
DC + AC .
two, when varied additional harmonics are created at the cut -off frequency of the new DC + AC setting .

The worst interference is the pulsing action generating high RF outputs .

The next question is — why does it affect hearing aids when the frequency range is –
20Hz- 20Khz (or less ) ?
That is easily answered in modern hearing aid –because they are run by a CPU processor which using PCM at a high frequency as well as wireless transceivers .

My own hearing aids are an example -processor controlled– adjust one and the other adjusts as well but each within the same range they were manually set at to keep the balance right (each ear can have different levels due to different hearing loss in each ear.

So yes that’s why Robert gets interference.

For those doubting me read and look at a modern hearing aid processor.-

It was your recent post that set me thinking about this, Duncan. I cannot find any information about the circuitry in LED lamps currently on same in the UK. I’ve only attempted to dismantle one LED – a GU10 dimmable one – but the circuitry was potted and not accessible. I no longer have an oscilloscope to look at RF interference. I certainly appreciate the potential of drivers operating at high frequency to create interference.

I presume that digital hearing aids are becoming more common and if they are more susceptible to interference than the older analogue type this may become a more common problem.

As you like professionalism Wavechange here is a US manufacturing companies actual circuits for dimmable LED,s –

Of course there are simpler circuits see-

Notice that the website says there are many varieties and that the National Electrical Manufacturers Association are trying to develop a Standard circuit .

For those quizzing my use of US circuits well unlike politics /society etc electronics is the same both sides of “the Pond ” .

Thanks again, Duncan. I am fascinated by electronic circuit design for household products. 🙂

I suspect that Infineon is producing designs and selling components rather than manufacturing LED lamps, and maybe for high quality products rather than inexpensive household lighting – but I could be wrong. The commentary in the article is interesting too.

As I read it, the idea is for NEMA to produce standards for performance and testing of dimmable lighting rather than standardise on the circuitry.

I suspect that different manufacturers of dimmable LEDs use different circuitry, as mentioned in the second article. I have a bedside light with a built-in dimmer and that behaves quite differently with different dimmable LED bulbs. With a Diall (B&Q) lamp it works fine on the three brightness settings but flickers or does not work on some settings with any of the other dimmable bulbs I have tested.

That was a point made on a website I was checking Wavechange that it depends on the actual circuit as to whether certain LED bulbs will work in a dimmable circuit controller.

For everyone new to the conversation – here’s the which? page on common problems with LED lights including interference. We had similar issues with our light fittings recently. Our landlord wouldn’t believe us until we showed him this page. We now have newly wired light fittings which solved the problem.


Thanks Abby. It might be useful to put this link in the introduction or maybe start a new Convo on LED lighting, since quite a lot has happened in the six years since this Convo was launched. One useful piece of advice that I’ve not seen anywhere else is to avoid mixing conventional and LED bulbs because the latter could be damaged by overheating.

In your linked article and in the magazine it is reported that Which? did not find interference problems but from this Convo, some have had quite serious problems. I wonder if Which? ever contacts anyone who reports problems on Which? Convo. Some of us would be happy to help and feel a little more engaged with our organisation.

It would be useful if Which? asked the industry for their comments on LED interference.

From the document mentioned by Abby: Our LED research In 2017, we asked 1,728 Which? members to tell us about any LED problems they’d experienced in their homes. We then consulted industry experts, and our top Trusted Trader electricians, to shed some light on what might be causing each issue – and how to fix it. According to our survey, 90% of members who have LEDs in their home are happy with their bulbs and the quality of light they produce. More than half haven’t experienced any problems at all when fitting their LEDs. Early failures (28%), flickering (12%), buzzing (5%) and radio interference (2%) were the main problems encountered. For more advice, see our guide to buying the right light bulb.

This suggests that radio interference might be a less serious problem than it used to be, but if 2% are still experiencing problems that is still not good enough. A lot depends on whether users were asked if they had experienced radio interference or had a problem with recent LED bulbs.

I was thinking more of getting an industry view on what standards must be met, how they mitigate interference to meet them and to what extent they find and test non-compliant imports. The Lighting Industry Association in the UK and the European Lamp Companies’ Federation might be starting points

I recall that you have mentioned the LIA before, Malcolm, and I would welcome their input. It does not surprise me that some of the cheap lamps sold online are non-compliant but a fair number of the posts refer to well known brands – for example the recent post about GE bulbs causing problems with a digital hearing aid. If there is a problem with fake lamps being sold under established brand names, the industry will be aware of this and should able to offer useful guidance.

I wish the lighting industry would encourage companies to provide useful information so that consumers have the information that they need at the point of sale. For example, although packaging shows which lamps are dimmable it should state that a compatible dimmer is needed. Using the wrong dimmer may be responsible for many of the cases of flickering mentioned above and possibly some of the failures.

Neil says:
23 April 2019

Just fitted 2 4ft LED battens in the garage and they totally block DAB and FM signals on my radio

I suggest you return them to the retailer for a refund, Neil. Can you tell us the make and model?