RF noise from LED flashlights

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RF noise from LED flashlights

Postby Toomas Losin » Sun Sep 07, 2014 2:43 pm

As I was listening to 1110 last night I had the lights out and was using an LED flashlight. I happened to put the light near the radio, which caused the radio to emit a blast of noise.

The flashlight (a Fenix LD01, an excellent small light using a single AAA), like many quality LED flashlights, uses an electronic regulator to maintain brightness as the cell discharges, and supports multiple brightness levels. Some quick testing showed that the brightest mode was quiet but as the dimmer modes were selected the noise level increased; the dimmest mode was the noisiest.

What's surprising is that this noise happens despite the entire body of the flashlight being machined from aluminum except for the glass front. The noise stopped when the flashlight was about 15 cm from the radio.

I tested some of my other LED flashlights and found the same was true. The dimmest levels produced the most noise. The noisiest light had a plastic body which, obviously, isn't much of an RF shield.

Another example of consumer gear producing crud on the AM band. I wonder if LED flashlights are required to be tested for RF emissions?
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Re: RF noise from LED flashlights

Postby skyvalleyradio » Mon Sep 08, 2014 11:17 am

Toomas - thanks for the info about LED flashlights & RF. I've just ordered one of these but will be careful not to use it when DXing with one of my portables. I have one 6v lantern with regular light bulb that I can use. Today, I purchased a few 10w LED light bulb replacements for my 60w desk lamps since they were on sale. I will see if these cause any RF interference when the portables are placed near them.
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Re: RF noise from LED flashlights

Postby jon » Mon Sep 08, 2014 11:34 am

When LED household light bulbs first came on the market at a relatively reasonable price for a useful amount of light output, I did some testing in the daytime on a decent AM receiver and a fairly quiet frequency that actually had a station on it (1180), and didn't detect any interference at all. Mind you, I stick to the major brands, mostly Philips as they are the easiest to find.

Toomas is probably right about the voltage regulator circuitry being the problem. I now have a lot of both household and flashlight LED bulbs, and haven't yet noticed any problems, but I will investigate further. None of my flashlights have, to the best of my knowledge, any regulator/brightness circuitry in them, and you can see them fade as the batteries get depleted.

My problem is AC Adaptors, including the new ones that provide USB power. That is where I plan to concentrate my efforts in the immediate future. Thankfully, most only need a couple of feet distance from the antenna for the RF interference on AM to disappear to nothing.

As for regulation, my understanding is that the FCC and Industry Canada both have a specific list of devices that they keep an eye on, and flashlights and light bulbs were never on that list, even the noisy fluorescent tubes of the 1960s. They peaked at 600 KHz and could make CJOR unpleasant to listen to half way across a house.
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Re: RF noise from LED flashlights

Postby Howaboutthat » Mon Sep 08, 2014 2:20 pm

Am I missing something?
Is this DXing by the light of a flash light a cult thing, or is there a reason you can't sit in a room with a normal light and turn the knob?
Houston, We're dealing with morons!.
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Re: RF noise from LED flashlights

Postby jon » Mon Sep 08, 2014 4:52 pm

I'm know that Toomas can speak for himself, but I know quite a few DX'ers who live in "impossible" RF environments, due to RF interference and/or RF blocking (steel rebars in concrete). The only way they'll ever hear anything interesting is away from home, or during a power failure. Since AM skip is generally limited to night-time hours, a source of light is usually a must.

Then, of course, there are those West Coast DX types who thought that the old CanCon favourite "Paradise by the Dashboard Light" was about driving out to the ocean and listening to ZCO come in from Tonga.
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Re: RF noise from LED flashlights

Postby Eldon-Mr.CFAY » Mon Sep 08, 2014 5:06 pm

Greetings, Thanks Toomas for mentioning that. I have an LED Desk Lamp which is battery operated and at least 5 LED Flashlights some in plastic enclosures. I have not had any problems with them generating noise when I am dxing here. However most of the time they are not within 6 inches or 15 cms. from my portable radios at all. I will check them out by placing near the portable AM dx radios here and see what happens. I think the closest I have had a flashlight or LED Lamp was maybe two feet. I just have the LED Lamp adjusted from that distance so it puts enough light towards where the radio is that I am using with a notepad for writing.

Again thanks for mentioning that Toomas. I know various types of electrical lighting connected to the AC outlets can cause some severe interference to listening and dxing on the AM band. So can my laptop computer here if the radio is within 30 cms. or a foot distance of it.

Take care and hope the electrical noise is low where you are if you are dxing!!!


73s Eldon
Bye . . Mr. CFAY "Frequently On The Frequency"
The CFAY Website: http://cfayradio.wordpress.com
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Re: RF noise from LED flashlights

Postby Toomas Losin » Mon Sep 08, 2014 5:41 pm

skyvalleyradio wrote:Toomas - thanks for the info about LED flashlights & RF. I've just ordered one of these but will be careful not to use it when DXing with one of my portables. I have one 6v lantern with regular light bulb that I can use. Today, I purchased a few 10w LED light bulb replacements for my 60w desk lamps since they were on sale. I will see if these cause any RF interference when the portables are placed near them.

I have a couple of models of Philips 800 lumen LED bulbs and all emit some RF noise but at different levels, even the same models, so they become quiet at different distances, from 20 to 50 cm depending on bulb. Still, many times I've had RF noise and on impulse I've turned off the lights but to no effect, so the LED bulbs weren't the source; however, knowing they do emit RF makes them suspects each time.

I doubt you'll notice a flashlight problem. I don't normally notice any noise if I use an LED flashlight around a radio; one has to bring it close to hear the noise, and some are quieter than others. But, I figure that all that quiet crud will add up to raise the noise floor.
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Re: RF noise from LED flashlights

Postby Toomas Losin » Mon Sep 08, 2014 5:46 pm

Howaboutthat wrote:Am I missing something?
Is this DXing by the light of a flash light a cult thing, or is there a reason you can't sit in a room with a normal light and turn the knob?

I'm not sure why I had the lights off in that room but I find that DXing in the dark or dim light does have a mystique to it. That possibly comes from starting the hobby while camping outdoors at night when skywave magically brings in the signals. It's like the darkness and DXing go together. It's like Old Time Radio belongs to the night because Network Replay aired late at night. Ahh, memories of the good 'ol days!
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Re: RF noise from LED flashlights

Postby dial twister » Mon Sep 08, 2014 6:22 pm

Howaboutthat wrote:Am I missing something?
Is this DXing by the light of a flash light a cult thing, or is there a reason you can't sit in a room with a normal light and turn the knob?



I was always warned that you'd go blind if you played with your knob in the dark. :oops:
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Re: RF noise from LED flashlights

Postby PMC » Tue Sep 09, 2014 10:26 am

Is this bit on LED's or RF... every human body generates RF noise, assuming it is a breathing specimen :lol:

Many good things will come from LED's.
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Re: RF noise from LED flashlights

Postby PMC » Tue Oct 07, 2014 11:26 am

Thought this CBC news piece fits in the topic of LED

http://www.cbc.ca/news/technology/nobel ... -1.2789832

====
Isamu Akasaki, Hiroshi Amano and naturalized U.S. citizen Shuji Nakamura revolutionized lighting technology two decades ago when they came up with a long-elusive component of the white LED lights that in countless applications today have replaced less efficient incandescent and fluorescent lights.

"They succeeded where everyone else had failed," the Nobel committee said. "Incandescent light bulbs lit the 20th century; the 21st century will be lit by LED lamps."

Red and green light-emitting diodes have been around since the mid-20th century and have been used in applications such as watches and calculators. But scientists had struggled for decades to produce the shorter-wavelength blue LED needed in combination with the others to produce white light when the three laureates made their breakthroughs in the early 1990s.
====
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Re: RF noise from LED flashlights

Postby Toomas Losin » Tue Oct 07, 2014 10:08 pm

Blue LEDs have indeed come a loooong way.

A few months ago I tore down a new Philips LED bulb which uses blue LEDS to light up a phosphor layer to produce white light. Those Royal Blue LEDs produced the most intense blue light I've ever seen. The room around me looked very weird bathed in pure monochromatic blue, and that blue light caused some materials to fluoresce. Be careful of the blue light hazard; don't stare into such bright blue light or play too much with it.

For a cheap but educational hack: Take a DVD or CD and use it as a diffraction grating to see what colours the light from different bulbs actually have. Compare incandescent with CFL and LED, or even street lamps. Good for an evening of fun!
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Re: RF noise from LED flashlights

Postby PMC » Thu Oct 09, 2014 5:14 pm

Toomas Losin wrote: Compare incandescent with CFL and LED, or even street lamps. Good for an evening of fun!


They stopped rolling up sidewalks in your neighbourhood ?? :lol:
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Re: RF noise from LED flashlights

Postby Toomas Losin » Thu Oct 09, 2014 9:10 pm

Nope, I still have my sense of wonder. :-)
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Re: RF noise from LED flashlights

Postby PMC » Fri Oct 10, 2014 9:34 am

LED's could be put into sidewalks, theyare in walls now... some neighbours light up their yards with solar powered LED's, sold at Canadian Tire. Have seen the same on balconies.
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