Some LED lighting products have been reported to emit noise, interfering with FM radio and DAB signals. While the Light Emitting Diodes themselves do not generate any detectable noise, the switching power circuitry driving the LEDs operate at high frequencies, which, when not properly filtered can result in electromagnetic interference.
Based on the reported experiences of some LED users, interference issues and, occasionally EMC violation, can arise as a result of radiated emissions in the 30MHz to 300MHz range by some LED products. The LED lights most commonly involved are of fixture type MR16 (more correctly GU5.3), however radiated emissions have also been observed in other fixture types including GU10, E27 and B22 designs. In the case of MR16 lights, the radiated noise signals would most likely be the result of the electronic transformers driving them rather than the lights themselves.
Electronic transformers are switched mode power supplies that switch the forward current on and off at high frequencies to minimize power dissipation. When these higher frequencies are not properly filtered, it can result in RFI emission. Signals most likely to suffer as a result of radiated noise include FM radio (broadcast band 87.5 to 108.0 MHz) and DAB radio (broadcast band 174 to 230 MHz).
The RFI emissions of a Dimmable A19 Globe manufactured by FEIT Electric was measured using a VHF antenna and a spectrum analyzer over the 30-300 MHz range. The LED light was found to emit significant broadband interference consistent with user's reviews, adding audible noise to FM and completely cutting out DAB stations. The instantaneous difference in the radio signal across the measured band when the light is operating and when it is switched off can be seen in the radio spectrum graph below. The peak interference generated over 30-300MHz is pictured in the figure above, the substantial noise generated over 94-110MHz (a frequency band containing popular Sydney FM radio stations) is highlighted in the red box.
Some FM radio interference has been reported on account of Click's 5W MR16 LED globe. The instantaneous change in the measured radio spectrum 1 metre from the LED light supplied by an OSRAM Redback electronic transformer can be seen in the figure below. The same light connected to a magnetic transformer was noted to also produce some, albeit significantly less, RFI.
The RFI emissions of a Dimmable Tube Light manufactured by EagleLights was also measured using the same test set up. In contrast to the previous two measurements however, the frames of the following figures reflect the maximum emission per frequency collected over one minute when the light was on, compared to when it was off. As evident from the graph below, it is an extreme case of the RFI that can be emitted by LED lighting products lacking adequate RF suppression.
A particularly severe case of digital TV/DAB signal disruption was caused by a Mirabella 5W MR16 LED light. High levels of RFI were measured regardless of whether it was supplied by an electronic or magnetic 12VAC transformer. The light's measured maximum RFI emission within the 30-300 MHz range can be seen in the figure below. The product has been reported by users to completely cut out digital TV and radio reception even affecting neighbouring houses. The experience of one such user spawned a whirlpool forum discussion
While there are cases of certain LED lamp products emitting RFI, most LED lamps, especially those from reputable lighting manufacturers, are designed with sufficient RF suppression so as not to exhibit this problem.
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