Reducing Radio Frequency Interference in LED Lights

By , November 2, 2015

Back in March of this year, I mentioned on the blog that our radio had developed interference when we turned on some of the cabin lights. A reader asked if we’d tried ferrite chokes. His question sent me on a rather interesting quest which has recently concluded happily for us.

It took me this long because none of the people I asked had ever heard of ferrite chokes, also known as ferrite beads, choke cores, and a handful of other terms. I researched them as well as I could on my own, and eventually ordered some from out of town. Hopefully, my newly gained education and experience in this matter will benefit others as well.

Apparently, LED lights can cause radio frequency interference, commonly referred to as RFI. It seems that cheaply made LED bulbs can cause havoc with radio reception.

The antenna takes a couple wraps through a ferrite choke  (Photo: Mark A. Zeiger).

The antenna takes a couple wraps through a ferrite choke (Photo: Mark A. Zeiger).

If you’ve ever priced LED lights for the home, you know that only the cheaply made ones offer affordable prices to the budget minded. Also, there doesn’t seem to be any way to learn which bulbs are better made than others except to try them out. The most economical and sensible method seems to be to buy the bulbs you think might work best, and correct any interference they may produce through other means. I discuss our LED lights extensively on the blog, culminating with Saving the Best for Last? One More LED Bulb.

Unfortunately, the literature on correcting RFI with ferrite chokes either lacks detail, or provides way too much for the average consumer. I downloaded a 12 page PDF article on the topic, only to discover that I could comprehend about one page’s worth of information! The problem and its various solutions was addressed in such dense technical language I couldn’t cut through it. Even the plainest passages, which spoke of where to place a ferrite choke on a wire, were expressed in symbols that hold no meaning for me, not having a background in electrical engineering.

Just about all I gleaned from the incomprehensible paper was that ferrite chokes work best if the wire they’re attached to wraps around the choke several time. The effect of the choke equals the number of wraps squared!

I also learned that ferrite chokes come in a dizzying variety of sizes and shapes, designed to cancel different frequencies of radio waves. I read this after I’d randomly chosen my chokes, largely for the price.

I could do little more than my usual, stumble forward with half an idea of what the job requires of me.

Before the ferrite chokes arrived, I’d already run our stereo’s antenna through the cabin wall to the outside. This did little more than increase static on the radio, sometimes even when we had no lights on at all! When the chokes came, I started with trying to improve radio reception so that I could tell if I happened to effect improvements in the system.

I wrapped our antenna wire about 3 times around a choke, and the reception cleared immediately. Not only that, but turning on the lights no longer had any effect on our reception.

Problem solved!

I don’t begrudge the extra ferrite chokes. I got a set of 10 for less than the cost of a single choke I found first in my search. I’m set as we expand our use of LED lights in the house.

Now, just as the days grow noticeably shorter, we can listen to the radio in the morning and evening with the lights on. In the months leading up to this adjustment, we lit the cabin with oil lamps at these times so that we could hear the news and other programs clearly. I’ll miss the ambiance, but since we generate our own electricity, but have to buy lamp fuel, those little ferrite chokes represent a considerable cumulative savings for our homestead. We’ll likely use oil lamps often this winter, but at least we’ve reduced this one significant draw on our resources.

2 Responses to “Reducing Radio Frequency Interference in LED Lights”

  1. Survival Skvez says:

    The issue isn’t the LED themselves, it’s the power supply for the LED (however you may have these in a combined unit and consider them to be the one thing).

    LEDs are non-linear devices, to feed the exact Voltage that gets the correct amount of power to them for optimum light without damaging them through too much power is difficult. So what most manufacturers do is they fed too much Voltage but rapidly switch it on and off so the average power remains at the sweet-spot. The LED is fine with this but the rapid switching of the power on and off produces the RFI. More expensive power supplies will try and damp this RFI at source, cheaper ones will do a less good job of this or just not care.

    It’s always better to (try to) suppress RFI at the point it is created rather than where it is causing the interference. Add the Ferrites to the power cable as close as practical to the LEDs lights themselves.

    You want the high radio frequencies on your antenna so I’m surprised that adding the ferrite to your antenna didn’t stop the noise but also stop the radio signal! The RFI must be a higher frequency than the frequency of the radio station you are listening to. It is not recommended to add ferrites to your antenna. But if it works for you in this instance keep doing it (I just don’t want someone else reading this thread being misled).

  2. Mark Zeiger says:

    Skvez, thanks for going into the details. Since most LED light “bulbs” come as a combined unit, I didn’t want to get too specific about why this is happening. Practically speaking, screwing an LED cluster “bulb” into a socket creates a problem to be solved.

    I started by putting the ferrites as close as I could to the bulbs, but heard no difference. Adding it to the antenna was a sort of “hail Mary” pass, but it worked.

    As my Website disclaimers point out, I’m not a certified expert on most of what we discuss here. The blog relates what we experience, and offers advice based on that experience only, unless I specifically research a topic. I think a judicious re-reading of the post reveals that I’m not saying this is what anyone should do, I’m just reporting on how we solved our problem.

Leave a Reply

Panorama Theme by Themocracy