# Traffic Lights and Radio

**URL:** <https://boards.straightdope.com/t/traffic-lights-and-radio/160592>\
**Category:** Factual Questions\
**Created:** [March 11, 2003, 5:01pm UTC](https://boards.straightdope.com/t/traffic-lights-and-radio/160592 "2003-03-11T17:01:30Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Arken](https://avatars.discourse-cdn.com/v4/letter/a/dfb087/32.png) [@Arken](https://boards.straightdope.com/u/Arken)\
**Post date:** [March 11, 2003, 5:01pm UTC](https://boards.straightdope.com/t/traffic-lights-and-radio/160592/1 "2003-03-11T17:01:30Z")

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I’ve lately been listening to an FM station (the frequency is 90.1) which is about 60 miles away. Unfortunately, it doesn’t always come in clearly and I get a lot of static on it. Recently though, I’ve noticed a strange phenomenon… when I am sitting at a red light, the static is much stronger. When the light turns green, there is a noticable lessening of the static. At first I thought it was simply that I moved my car when the light turned green and was back in range to pick up the station more clearly, but I’ve definitely experienced this before moving the car on an empty street with no other cars moving that might affect the signal. What gives? Why would the traffic light be using an FM frequency even if it did use radio to somehow control the change? Wouldn’t it be more logical to use a frequency which wouldn’t affect a driver’s radio?

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**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\
**Post date:** [March 11, 2003, 5:15pm UTC](https://boards.straightdope.com/t/traffic-lights-and-radio/160592/2 "2003-03-11T17:15:19Z")

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Can you tell if one color light (probably red) is made of LEDs, while the other is a regular incandescent?

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**Author:** ![Arken](https://avatars.discourse-cdn.com/v4/letter/a/dfb087/32.png) [@Arken](https://boards.straightdope.com/u/Arken)\
**Post date:** [March 11, 2003, 7:21pm UTC](https://boards.straightdope.com/t/traffic-lights-and-radio/160592/3 "2003-03-11T19:21:04Z")

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I really wouldn’t know how to tell. The lights in this town were for the most part all reinstalled recently and now have a sort of high-tech countdown on the crosswalk and such. Would that make them LEDs?

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [March 11, 2003, 7:30pm UTC](https://boards.straightdope.com/t/traffic-lights-and-radio/160592/4 "2003-03-11T19:30:11Z")

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LED traffic lights are made of a dense pattern of distinct separate dots of light. Once you’ve seen them they’re fairly easy to recognize.

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**Author:** ![Arken](https://avatars.discourse-cdn.com/v4/letter/a/dfb087/32.png) [@Arken](https://boards.straightdope.com/u/Arken)\
**Post date:** [March 11, 2003, 7:32pm UTC](https://boards.straightdope.com/t/traffic-lights-and-radio/160592/5 "2003-03-11T19:32:59Z")

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> [@](#):
>
> \*Originally posted by Q.E.D. \*  
> \*\*LED traffic lights are made of a dense pattern of distinct separate dots of light. Once you’ve seen them they’re fairly easy to recognize. \*\*

Okay then… as far as I know, pretty much all of the lights in this town are LED. This also happens at multiple lights, not at just one light in specific.