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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.