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Led lights interfere with TV reception


etu

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We were watching the TCU and Texas Tech game last week while camping in our 5er in Cloudland Canyon in NW Georgia. I turned on a light to read and when I turned on the led light it killed my tv signal (winegard antenna). Turned the light off and the program came back on. I tried several other similar led lights but none of the others affected the TV. I replaced the led in that recepticle with the original standard bulb and it did not affect the TV. Btw the game was a great one and Cloudland is a nice state park.

Anyone know why this could happen?

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Based upon my experience in the field, which is a bit dated since I've been retired now for some time, I'd guess that there is probably a problem with the circuit of the leds. If your light is like most, it has more than one led and several other components, all mounted on a circuit board that inserts into the light socket. It is probably a problem on that board that was not always thee, but possibly is a design problem. If it never happen in the past, I'd look for a replacement led assembly. I have only once heard of that sort of thing with an led light in the past but it used to be fairly common for florescent lights. What is probably happening is that the led assembly is generating and transmitting rf interference.

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The "GRV T10 921 194 24-3528 SMD LED Bulb lamp Super Bright Warm White AC/DC 12V-28V" bulbs that I bought from Amazon all produced significant interference on some analog cable TV channels. The amount of interference varied with the cable channel and the distance of the light fixture from the TV. There was not any visible interference on the satellite channels. Other brands/designs of LED bulbs placed in the same light fixtures do not produce any visible interference.

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I had a similar problem. I'd be watching TV in the living room and all the sudden the station would go off. I finally realized it always happened when my wife went up to the bedroom and turned the light on. It only happens on certain stations. We just live with it as it's only the one set of LED light that do that.

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LED lights are not simple glowy things like incandescent light bulbs. To get the benefits of LED, you have to be pretty smart.

 

Smart, in this case, usually means pulse width modulation:

 

http://www.eetimes.com/document.asp?doc_id=1281013

http://www.k0bg.com/rfi.html

 

Even if you don't get a "dimmer" knob to play with, does not mean that the factory did not implement the PWM dimmer circuit and simply nail down the knob's value with a single-value resistor.

 

Want to set PWM in action? Next time you are behind a car at night, shake your head back and forth as fast as you can while keeping your eyes open. Standard incandescent bulbs in the vehicle in front of you will appear as the smudges of light that you'd expect. LEDs driven with PWM will appear as discrete dots of light. In effect, you are engaging in stop-motion stroboscopic vision as the LEDs flash ON OFF ON OFF ON OFF ON faster than you can detect (like a TV or movie being too fast for you to see the individual picture elements change).

 

Even funner? Bite a popcicle stick between your teeth and pluck it like a guitar string. As it vibrates your skull, you might see the secret morse-code message that those crafty EEs are embedding in brake lights!

 

Anyway, PWM, as implemented by lazy ignorant trolls, is a generous provider of all sorts of bad radio frequency interference.

 

 

All the best,

 

David

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Thanks for the explanations. I was worried something weird was going on in the wiring. Glad to know its just the bulb. Ill try replacing that led with another and see if it matters. Glad I realized the connection and switched that led out. I'd been real disappointed to miss that TCU and TX Tech game. When the loser scores 52 pts you know you've seen a lot of good football.

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Just read on an agtalk forum this explanation about some led lights causing problems with radio reception in farm equipment.

 

"Some early imported LED's gave off a lot of radio interference. Newer ones meet new standards and have a label 'Class B' and will not cause has much problems. If your LED's don't have the "Class B' label, replace them"

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As etu & TCW mentioned, the voltage regulators in the LEDs designed to operate over a wide range of voltages (12 - 30 volts or so) can cause EMI. The newer designs produce less, but if you want the quietest, look for the non regulated 12 volt LEDs. I have non regulated, 12V panel LEDs in my trailer & they have had no failures over the last 4 years. They are usually less expensive, and there is the possibility that high (for example battery equalization) voltages will damage them, but they are cheap enough that buying a few extras & replacing them is practical.

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If you have a LED lamp that you're going to trash, you might want to dissect that little beast and let us know what you find inside.

 

You might find a little chip with numbers like one of these:

 

NCV7691
ASL1010
TPS9260
Not that there's much to do with that information, other than impress folks at happy hour.
If you tell the manufacturer/seller why you're trashing it, they might be less likely to fob this kind of thing off on an unsuspecting public, too.
Anyway, it's not you, it's them.
:)
David
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