A first. For me anyway.

[Swollen Tongue]

Had a call today to meet a comcast tech at a certain location. He was getting interference on their phone customers on that street after dark. Found a street light that was cycling on and off. when the light would cycle off, that is when the interference would start. When the light cooled and came back on, the interference would stop. Nothing on the pole but a light and a duplex. nearest comcast trunk or drop was 150 to 200 feet away. Backlot lines in this area but this light was on the road. He said it wasn't affecting the tv at all, just their phone service. affecting quite a few of their customers.Just installed a new bulb and problem was fixed. Just would like to connect the dots on this one.

[T-Man]

Was that a sodium vapor bulb and fixture?

[Swollen Tongue]

Yes 100w high pressure sodium.

[BigClive]

It would be the high voltage spikes from the ignitor trying to reignite the lamp. It's a series of high voltage spikes that would create a sharp buzzing noise. Very audible on a phone but way below the frequency of a TV signal.

[T-Man]

Old sodium bulbs (ones that have been in service a while) develop a very small sodium leak and the bulb starts to be unable to support the arc which makes the light, they cycle off and cool down then come on again and take time to get to full brightness. The bad bulb will have dark residue toward the ends of the arc chamber. There is a pretty high voltage from the fixtures transformer (Igniter) to get the arc to jump the gap at the start of the cycle, once the arc is made the voltage lowers to support the arcing. Like Clive stated it's the igniter making the static while trying to restart the lamp.

[Swollen Tongue]

It would be the high voltage spikes from the ignitor trying to reignite the lamp. It's a series of high voltage spikes that would create a sharp buzzing noise. Very audible on a phone but way below the frequency of a TV signal.

I've seen a YouTube video on this before and this is a reasonable explanation. In the video, the interference was limited to a fairly small area. Only thing is we have lights all over the system that cycle. Just hard to understand how this one could cause this much interference to this many customers and at the distance involved. Don't know how many were affected, Comcast guy said the whole area.

[BigClive]

It could be that there was a grounding issue with the fixture that was allowing leaky ignitor current to interfere with adjacent low voltage wiring.