[RFI] LED traffic signals

Donald Chester k4kyv at hotmail.com
Fri Dec 14 15:43:08 EST 2007

I  live in the country with no traffic lights nearby, so this isn't a problem with me, but I keep hearing about RFI generated by the new l.e.d. traffic signals.  Apparently, the noise is due to a switching power supply used to feed the lights, and the power line leading to the unit acting as an antenna.

Someone I know has one of those LED stoplights about 100 yards from his house.  It wipes out the AM BC Band when you are in the car sitting at the light, and he says he can hear it up and down the band and  weaker signals on 75 and 160 at night are GONE.  He figures there isn't anything he can do about it at all, except move.

I wonder if anyone has checked to see if those led traffic lights have been certified to meet Part 15 standards.  Since they are becoming ubiquitous in almost every city and town and there are traffic lights literally everywhere, this could grow into a major rfi problem that rivals or surpasses BPL.  

Perhaps the AM broadcast industry would get involved, since this stands to hurt them severely.  Over 90% of the prime time radio audience during morning and evening hours is made up of commuters, and most listeners will simply switch over to FM if they start getting interference at every traffic light.  This could become the death knell for AM broadcast radio, with its odds for survival already marginal at best. Those switching power supplies could easily be fixed with a little filtering.  I'm not even sure that shielding would be required.  

This is a problem that needs to be addressed NOW before the overwhelming majority of traffic signals nationwide are replaced with noisy l.e.d. ones and the problem becomes impossible to remedy.

Don k4kyv

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