/ 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.

Mike Smith Engineering says:
22 March 2013

Having spent many years within the EMC world cheap LED lamps do indeed emit high levels of conducted and radiated emissions. However there is a more sinister problem associated with the use of LED lamps which is the strobe effect on rotating kitchen equipment such as food mixers etc. which can appear stationary though moving at speed. This the same problem as with fluorescent lighting on machinery in factories in the 1950’s which was remedied by ‘lag lighting’, which cancelled out the effect. A case of history repeating itself!

Bob Bohannon says:
25 March 2013

Interesting on the effects of flicker. You are correct that 50 Hz flicker caused machinery to look stationary, this was solved by using high frequency ballasts.

I’m not an electronics engineer, but the problem with LEDs is probably the dimming method which is often pulse width modulation (PWM). I assume too slow and you see the stroboscopic effects.

PeterG says:
22 March 2013

Have replaced 4 GU10 220v halogen with 8 LED downlighters in the kitchen completed about 2 weeks ago. Crown DAB 220v radio with telescopic aerial sits about 3 foot underneath the nearest one and continues to work perfectly.

The lighting is perfect for a kitchen and much brighter and cleaner.

The LEDs units were Megaman dimmable reflector PAR16 – 500cd WFL35 CRI Ra (80). 25000hrs; 4000K cool white 410 lumen 6W GU10. They don’t come cheap, each bulb will set you back about £13. Clearly this product does meet EMC EN standards.

You get what you pay for with LEDs, if you are replacing a 50W GU10 halogen you will need at least a 500cd (candela) or 400+ lumen LED light to get anywhere near the same output. The number of LEDS is irrelevant, the more there are the more likely they are cheap and inferior and more likely to fail.

Changing the subject slightly I wonder how many people realise that many of our modern traffic lights are now only about 6 LEDS with a 400cd light intensity, operating at 11 watts during the day and dimming to around 4 watts at night. All with a lifetime of 7+ years and EMC approved. (yes I am in the traffic business)

Peter G, coloured lights – traffic lights as you say, car indicators and tail/stop. airfield and aircraft and other coloured signals are ideal applications for LEDs now their output is increased – they have stable colour, long life, are dimmable without changing colour and allow good optical control.
I remember when designing airfield lights where we used tungsten lamps with glass filters – the red filter glass changed colour with heat, and the lamp became whiter as the power increased, making keeping the signal colour acceptable quite tricky.

White LEDs are improving greatly, but good quality ones of good colour do not come cheap. Generally avoid large numbers of low power ones crammed together; better to go for higher power ones ( 1 to 3W each) which are likely to have decent heat sinks to get the heat away.

Malcolm – I am far from happy with the way LED lights are used on some cars. It’s unpleasant to be behind a stationary car where the driver keeps their foot on the brakes or the indicators are on for an extended period. It is truly amazing that manufacturers cannot see the problem and fortunate that not all models with LED lights share this problem.

I used to make the same complaint about drivers whose brake lights stayed on at traffic lights but now I am one of them! The problem is that many modern cars have electronic braking when stationary at traffic lights and so on. There is little choice for the driver.

Your previous contributions made sense, tonyp. 🙂

Here is not the place to discuss the deficiencies of modern handbrakes but like LED lamps that create interference it’s another example of unsatisfactory design.

Please accept my apologies, wavechange, I didn’t realise that you were controlling the content of this thread. I was merely trying to point out that your comment about drivers keeping their feet on the brake pedal may not always be correct.

The Highway Code instructs drivers to take their foot off the brake when stationary to avoid dazzle, and has done since before LED lamps or electric brakes were first fitted to vehicles.

All discussions about any LED lights and interference are on the table – we’re interested in all your opinions!

John Dalton says:
28 March 2013

I’m intrigued about use of LEDs in cars – have they at last changed the old “Construction and Use Regulations” which REQUIRED side lights to be 6W – ie. specifying the power consumed rather than the light emission in lumens? A 6W LED would be blindingly bright!

Unfortunately we would have to buy a set of the regulations if we wanted to inspect them, John.

I contacted Mercedes after being being blinded when stuck for ages behind a car with particularly intense brake lights. I was told that they use LEDs to provide longer life (fair enough) and to save energy (I had not realised that Mercedes had grasped this concept). The person I spoke to seemed unconcerned that I found it uncomfortable to have these blinding lights in front of me. I have no problem with LED lighting on vehicles as long as it is sufficiently diffused and the viewing angle is adequate. The way that some manufacturers seem to adorn their cars with strings of LEDs suggests that they cars should come under the regulations for decorative lighting.

I assume that LED lighting in cars does not cause interference problems. It operates from low voltage, so there is no need for interference-generating power supplies.

Ignition systems in petrol-engined cars used to cause radio interference and the early capacitative discharge ignition systems of the seventies made the problem worse, but manufacturers have overcome the problem. Hopefully a little effort will do the same for domestic LED bulbs and their power supplies.

Roger says:
22 March 2013

Old-style incandescent light bulbs are purely ‘resistive’ technology. Apply a constant voltage of the correct value from an electrical power source that can deliver (at least) the required current and your bulb emits light as the current heats the element until it glows.

For DC (typically battery fed) bulbs, the electrical flow is in one direction only, so no radio frequency (and therefore radio frequency interference = RFI) will be emitted.

For AC (mains powered) bulbs, the 50Hz oscillation of current flow in the wires feeding the bulb, creates magnetic flux – building and collapse of magnetic fields around the wire as the current flows back and forth like a tide. The rate of oscillation (current flow reversal) is 50Hz in the UK (50 times a second) – this creates RFI, at 50Hz.

No modern radio or TV will detect it, they are ‘listening’ for signals at much faster frequencies and are ‘deaf’ to such slow pulsing. Many DAB radio broadcast frequencies are in the 220MHz area of the electromagnetic spectrum. 220MHz is an oscillation occurring 220 million times a second, no wonder a mere 50 times a second seems slow !

LEDs with excellent (and improving) light output / Watt, superb longevity and indifference to on/off switching, have been released into a world where electrical power is supplied in differing levels of constant voltage eg 12V dc, 240V ac and so on.

LEDs aren’t happy with that, but require constant current instead. To convert from the normal constant voltage supply to constant current supply, so the LEDs will work, requires a ‘power transformation’ circuit, the commonest of such circuits are called ‘switch mode’ circuits.

Unfortunately the wide-ranging frequencies that can be output purely as an unwanted by-product from switch-mode circuits, includes the range of frequencies we use for transmission of broadcast radio programmes eg 220MHz, and therefore detected by our broadcast receivers !

By the way LEDs are not the only household items that use similar power transformation circuits, so don’t just blame the poor LED, unless it really is the RFI emitter amongst several in your house, that is to blame !

Differing designs of switch mode circuit can lead to differing levels of RFI being output as a by-product of the power transformation. The stronger the emission the further it will carry and cause interference.

Differing care by various manufacturers captures that RFI in shielding to prevent (or reduce) the RF escaping from the process, to a small amount or none at all. So a whole range of power transforming circuits, driving LEDs amongst other items ‘out there’, line up on a spectrum from ‘clean’ to ‘very dirty’ in terms of how much they emit RF which potentially interferes with your broadcast receivers ‘listening’ out on certain frequency ranges (the tuning range of your receiver).

Analogue (pre-digital) receivers ‘coped’ with the interference but their sound output was compromised by a background or sometimes over-powering, foreground white noise.

Digital equipment tends to either be able to ignore RFI (you don’t even know its happening), or is completely knocked out by the RFI, giving the appearance the receiver has failed when in fact it has been disabled by the RFI from a nearby switch-mode circuit’s by-product !

Sadly as our electronic technologies evolve to become ever more complex, negative interactions between them become ever more numerous and occur in an increasing range of subtleties.

Broadly speaking CE-approved equipment is on the whole ‘cleaner’ in emitting little or at least, less, RFI. But as other contributors have noted, even selecting CE-approved kit, is not an absolute guarantee of quality in respect of RFI !! If you are suffering from RFI and you have identified the piece of kit that is the cause – complain to the manufacturer and ask for re-dress.

Sarah says:
23 March 2013

I recently installed some very expensive warm white solid state LEDs in my kitchen in 2 zones of 12 and 4. When they are switched on they interfere with DAB and FM to to a lesser extent. I have been in contact with the manufacturer and at first they blamed a weak radio signal, but then admitted they have had this problem a few times before. The lights conform to emission regulations and I believe in singles would not interfere with the radio signal, but LEDs need to be used in multiples because the light does not spread so i suspect they then surpass the emissions regulations when aggregated together. The zone of 4 causes less interference than the zone of 12, and both together often knocks the signal out altogether. The manufacturer has tried to be helpful but the transformers on each light would need to be replaced to stop the problem and they have not come up with an alternative so we are going to try Internet radio instead. The thing that annoyed me most of all is that the manufacturer knew of the problem but did not design the problem out, which is entirely possible to do.

Andrew says:
23 March 2013

It’s possible that you get what you pay for. I bought some cheap generic LED bulbs from LED Hut and yes, they did cause radio interference on long and medium wave AM stations. It sounds like a buzz at twice mains frequency (i.e. 100Hz). It is generated by the switched mode power supplies built into the base that turn the high voltage from the mains into the low voltage DC needed to light the LEDs.

Unfortunately, these switched mode power supplies generate radio waves modulated at twice mains frequency as a byproduct. This is you hear on you rAM radio set. In the case of DAB, you cannot normally hear it but if the the signal is weak or the interference is too strong reception falls off the “digital cliff” and you hear either burbling noises or you hear nothing.

The power supplies in the bulbs should contain filters that remove these radio frequencies, but in cheaper ones these may be inadequate or not present at all.

“Which” needs to do a survey of all readily available LED bulbs to see which ones emit least radio frequencies, particularly since the World Health Organisation has recently classified radio frequencies as being a Group 2B carcinogen.

Andrina Nisbet says:
23 March 2013

I do not receive digital radio here in Yell, Shetland, but low energy bulbs also affect LW and FM radio signals.
The bulbs which affect the radio are Memolux 20w bulb and Everready 7w Candle bulb. They do not seem to affect MW radio signals.

Barrie P Spink says:
23 March 2013

I am a Radio Amateur and are regularly working with weak signals that are swamped by interfering signals generated by phone chargers and similar power supplies, computer power supplies, LED bulbs, solar panel installations and CFL’s. Almost all these interfering items seem to have one thing in common, the necessary filtering circuitry has been omitted from the electronic circuitry. We send details off to our national society (The Radio Society of Great Britain) who have the means to test the items and publish the results in our monthly magazine. In many cases the items do not conform to the regulations and should be dealt with by Trading standards, other cases the equipment is very new and the regulations have not caught up with it. Either way there could be many millions of the items out there.
The case of some solar power installations is typical, to keep the price of the installation down the interference suppressing components are missed out, the premise being that if there is a complaint then they can always be retro fitted later but at whose expense.
For interference to Radio and TV OFCOM and the BBC offer a service to trace and advice on a cure for this kind of problem.

The only complaint route seems to be through trading standards who are hopelessly under-resourced to deal with this sort of problem. They also, I believe, generally need multiple similar complaints before they might react – not very likely to happen.
You could take these issues up with the Lighting Industry Association (www.thelia.org.uk/) who represent reputable manufacturers and will be keen to eliminate non-compliant products that normally come through importers.
Alternatively perhaps Which could collate makes of offending LED eqipment (electronic controllers particularly) and take the issues up through LIA or Trading Standards.

My non-dimmable LEDs (3000k 12v LED bulbs) cut the signal to my DAB radios including the radio upstairs even though all the LLEds are downstairs completely. They are generic bulbs.

The dimmable (same maker) GU10 3000/4000k (a mix) LED bulbs do not nor cause any interference whatsoever.

Susan Tritton says:
24 March 2013

I have noticed considerable interference with my (analogue) radio – particularly on long wave. The interference is from low energy fluorescents…. a present “culprit” is GET H292603 2700K Warmwhite.

You could struggle to long wave reception because so many modern devices cause interference. It is easy to explore sources of interference with a battery-operated portable and using this sort of radio rather than a plug-in radio will give some protection from interference carried in the mains supply.

If I wanted to listen to long wave Radio 4 transmissions I would probably listen via the Internet:

Kevinuk says:
24 March 2013

I have a GE 4W LED, controlled by a dimmer, immediately behind a Samsung 37″ LCD TV and have not experienced any problems.

Peter D. Smith says:
25 March 2013

I have just replaced a 50 watt halogen GU10 -one of a cluster of three mounted in an earthed
metal framework- with a Meridian type GU6WW white light ‘high power’ LED, having a consumption of 5.4watts at 230 A.C. 50 Hz.and a claimed life of 35,000 hours.
This LED lamp causes a buzzing noise in my radio when on FM.
The radio, situated about 1 metre away, is a Sony FM-MW/LW type ICF-M50RDS which I only use on FM. There is no interference on A,M, MW/LW
I also have a DAB radio- Sony type XDR-S55DAB- which I placed about 1 metre away from the LED lamp but did not get any interference.
Both radios run from the A.C. mains- not from their internal batteries.
HOWEVER- I have CURED the interference on the FM radio by connecting the ribbed
aluminium shell (heatsink) of the lamp, to the earthed metal lampholder.
I did this by pushing a scrunched up small ball of aluminium kitchen foil between the lamp shell
and the lampholder (There is no danger of it touching the Live and Neutral mains connections).

Dimming LEDs is often done by switching on and off rapidly – by varying the length of the on period and the off period the (effective) light output is changed. In fact this I believe can also be used to control a non-dimming LED. I sometimes see what appears as a string of images from car tail lights and amber road works lights which I presume is down to this.
LEDs are constant current devices (d.c.) – light output is governed by the current pushed through them – best using a constant current electronic controller which would not produce flicker.

I understand that LEDs are pulsed to make them appear brighter than if fed with a constant current.

Some people seem to be much more responsive to the flickering revealed by movement, mentioned by Malcolm. I’m one of them.

john wall says:
25 March 2013

I have had the same experience with some LED light bulbs.

I bought quite expensive bulbs to fit into downlighter sockets for 12 volts bulbs, also some cheaper ones for downlighter 230 volt bulbs

The 230 volt bulbs cause no interference with my digital radio.The 12 volt ones interfered so completely that output was stopped completely – these were Kosnic bulbs at ~ £15.00 each!.
I contacted Lustrum and they checked on their bulbs for 12v and experienced no problem with a digital radio. I bought these at about £6.50 each! and they work fine with NO interference. They did warn me that using thes bulbs with a regular transformer the bulbs would be (might be) destroyed. I took a chance and so far – 3 months all is OK.

Chris C says:
25 March 2013

I purchased a Roberts Ecologic1 at the same time that I replaced the bathroom lights with LED’s from LEDHut. I just accepted that there was no reception in the bathroom but following your article I tried with the lights OFF. The radio worked fine! Bathing in the dark from now on

Roderick Goodall says:
25 March 2013

I live in an apartment in a grade 2 listed building where satellite dishes cannot be installed. I use BT Vision with the Hub in one room and the vision box and TV in another. The ethernet connection between Hub and Vision box is via the apartment’s 240 volt wiring and BT’s latest ethernet power sockets. The replay system on i player, or pay for view becomes very broken and disjointed, to the extent that it is not watchable, if we have 3 table lamps on in the sitting room. These are connected to wall sockets in the sitting room positioned between the TV and Hub. The lamps are fitted with long life bulbs.
Turning them off, immediately restores the picture and sound to a watchable standard.
A Sony blu-ray player is similarly degraded.

Dave B says:
25 March 2013

Classic EMC troubles. (ElectroMagnetic Compatability.)

Just about all LED lights use “switching regulators” that work at a high frequency, carving up the incoming mains (or low voltage DC) so they can regulate the current through the “lamp” in an efficient mannor. It is the resulting noise, an unwanted by product of the way they work, from these switching converters that is getting out into the environment, and causing the problem with broadcast (and other) radio. It’s a form of polution if you like, just that in this case it’s affecting the “Spectrum” that is also used by radio services.

The better (usually higher cost) LED fittings, have filters to keep the noise in, also, the converters themselves are better designed so as not to create too much noise in the first place.
Compact Flourescents can also cause trouble in the same way, but also radiate the “noise” in the form of varying light levels, way beyond what our eyes can detect, but other system (some infrared remote controled entertainment systems for example) can detect it, and it affects the way they behave, or misbehave when the light is on.

There is also an issue, where low voltage halogen lamps are often replaced by LED “bulbs”. The “Electronic Ballasts” (more switch mode power regulators) often misbehave with a low power load, and create a noise that their filters are not designed to handle, so causing even more noise for DAB and FM. Sometimes, if you put back one Halogen lamp, the problem is reduced, in that case, it’s almost certain it’s the fittings low voltage ballast that is causing the noise, as with a low power load, it is not working within it’s designed regulating range of power levels. Some will even flash once, then shut down, resulting in darkness!

The comments re CFL standard lamps affecting BT Vision, is also an EMC related issue, in this case the lights may be injecting high levels of noise into the mains wiring, affecting the Power Line Networking adapters that some/many BTV systems are using to connect between the box and the router. Quite why, they use significant power too when you think they are often left switched on 24/7, may have data security issues if not setup correctly, and while CAT5/6 cable is cheaper uses less power and works better anyway, but you have to hide it somewhere, so people take the easy (if expensive) way out, and use PLT, just so they don’t have to hide wires.

Power Line Networking adapters too, can interfere with radio services, the early ones mainly with Shortwave broadcast’s and similar, but the later GigaBit systems, can (do!) cause extensive interference to not only FM radio, but DAB too. Domestic mains wiring was never designed to carry high speed data, and does actually make a good unintentional antenna, especially with systems like the infamouse “landing light” where two or more switches control one set of lamps. The problem with that, is there are lots of wires that are “Live” without any corresponding Neutral, so radiating any power line noise, data, whatever rather well, too well. It’s a two way street however, as “interference” can also get in that way, from passing taxi’s, local radio transmitters and the like, disrupting the PLT systems.

Some PLT systems too, have been demonstrated to cause trouble for the higher speed broadband services such as ADSL2+, sort of ironic realy, and daft in the extreme.

Ofcom (the regulator) knows all this, but chooses not to “regulate” according to the rules, they have the statutory power, but probably for cost savings choose not to. They are funded from central government, who in turn are funded by contributions from industry, who make/import these things.

Trading standards are toothless, as unless you and the supplier reside in the same area, they seem powerless to do anything.

EMC is also a highly technical area, is not easy to measure accurately in “Real Life” what is going on, and even when it can be done, each case is often very different to others in detail, and difficult to compare.

The industry as a whole as clearly set standards and tests to measure such things, but even then, items are only tested in isolation, not as a group, or part of a combination of items, so the real cumulative impact of a lot of “Power Saving” technology, is not yet known, in regards to the electromagnetic noise it creates, and the problems it causes to many radio based services.

The problem/issues are only going to get worse, very much worse, before it will be largly noticed by the public and something is done. Solar PV systems too can create huge levels of interference, as can many other modern systems. Replacement PC Power supplies (both desktop and laptop) are another source. Often illegaly imported and sold without any filters in the incoming mains feed, resulting in mayhem in some situations. You can’t tell from the markings on the box, it’s only when in use, or if you take them apart and inspect, you find the problems.

All the “left out” parts save money and lower costs of course. It’s even been said (wrongly) by some, that such filters are only needed to pass compliance testing. Thats the whole point, they are needed to keep the noise in / not let it out.

Feel free to contact me for much more info if needed, the supplied email is valid.


Dave Baxter.

David Snell says:
26 March 2013

The problem is the poor quality switch mode power supply unit in the cfl or led which Mr Baxter described as “switching regulators”.
They do operate at a high frequency and are notorious for producing RF interference when badly designed. Even if they are CE marked they may not be compliant with the EU EMC regulations.
The RSGB has an EMC committee who investigate these issues and I suggest you liaise with them.
I am sure they will welcome your support

Ken says:
26 March 2013

There are 2 problems, both originating at the switched-mode power supply built in to the bulb:
– conducted interference, carried on the mains wiring: this is likely to be fairly minor and, if it’s a problem, then a ferrite bead threaded on the mains lead as close to the lamp as possible should reduce it.
– radiated interference: a more intractable problem. Falls off quickly with distance from the lamp. Can’t easily be fixed except by the lamp manufacturer: the bulb should be lined with an earthed metallised coating. Most of such coatings are opaque, although translucent ones are available. They will make the bulb significantly more expensive.
There are regulations covering these issues: if the manufacturers do not comply, then legal remedies are available.

John Dalton says:
28 March 2013

I’ve tried putting massive ferrite rings with several windings of the cable supplying bad interference producing MR16 LEDs. Fed from a 12v magnetic (50Hz) transformer via a 6ft cable, I couldn’t stop the FM radio squelching effect. The best improvement I could get was cupping the transformer in my hand, and placing my bdy between it and the radio!

Heather says:
26 March 2013

As an interesting addition to the forum, as well as having the problem with 12v LED and digital radio in my kitchen, I also experience interference when I open the fridge door and the light comes on!

As I have posted in the forum about the phase-out of incandescents I installed four LEDs last August. Although the do not cause any trouble with my TV (I don’t have a DAB radio) they do buzz and so far three of them have failed. They were not cheap and were bought from a reputable supplier (SimplyLED) At around £15 each they were not cheap.

So far they have replaced one of them under guarantee and I am waiting to hear from them about the others that have failed since.

Thay claim that the problem might be due to voltage spikes – but I know for a fact that my grid supply is within tolerance as I have had it checked over a period of weeks with a recording voltmeter following problems with dropout on my solar-voltaic installation. There were no spikes and nothing out of tolerance.

If these LEDs are unable to cope with voltage variations of less than 10% then they are not up to the job.

Wayne Goff says:
26 March 2013

As already stated in many of these posts, almost all electronic equipment will emit spurious radio frequency energy, and to place goods for sale on the European market, these emissions must be controlled and not exceed defined levels as required by the EMC Directive 2004/108/EC. It may be worth conducting a limited EMC test programme to determine how much these LED lamps exceed the limits by. This could then form the basis of a complaint to the manufacturers/importers and Trading Standards.

I believe the applicable standards are the EuroNorm (EN) standards. I would suggest contacting TUV in Fareham or similar EMC test laboratory who will be able to advise on this subject and suggest a series of tests to perform.