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In my experience a fully-centralised switch is actually quite uncommon.

In many locations they use light sensors, and if you live above a street oriented the right way you can see quite a cool effect of the lights going off sequentially down the street as the light goes below the threshold.

In other locations that I'm familiar with, they use a ripple relay, where a particular signal is transmitted over the power lines (a "ripple") in a way that doesn't affect unaware equipment, but signals the target equipment (relays on the supply to the streetlights) to switch. Similar technology is used to provide day/night rates where one circuit is only energised during off-peak hours.

I don't see any reason the ripple relay couldn't be bypassed to provide a second always-on feed for the Wi-Fi gear, but it might be that the ripple relays are not at every lamp post but instead at the substations or roadside cabinets, in which case there would indeed be some cost to run the extra circuits.

I previously worked at a company that made the light-controlled switches that control individual street lights. We shipped a lot of them, so I assume they are common. They are visiable and you can often spot them. They look like a plastic bulb on top of the light fixture.

At one point we came out with a slim line (low profile) design. When I asked why, they said that good ol' boys in Texas were riding in pickups and shooting the switches as a game. The low profile model was a harder target to hit. :-)

I am surprised Google was surprised, perhaps you were working with more modern infrastructure? Commercial areas?

I ran into this same problem in a the first 3 municipalities around 15 years ago when we tried deploying a street light solution.

> In my experience a fully-centralised switch is actually quite uncommon.

Just to offer a counter-point, in my experience it's often that they are managed in big groups, and individual control is uncommon.

Quite often at the right time you'll see big swathes of lights turning off, sections of neighbourhoods, as far as you can see down a reasonably straight road, etc.

From what I understand, it's usually just a timeswitch in the circuit breaker box at the side of the road.

Hard to say; it could be time control or ripple control of relays at substations, which would explain neighbourhoods turning on/off at the same time. It's still not fully centralised, and the more "decentralised" (I cringe when I write that word these days) it gets, the cheaper it gets to provide an always-on supply to the lamp post.

Thanks, that was quite an interesting read.

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