How do street lights work?

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MurrayM

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#133655 29-Oct-2013 17:06

The street lights in my street have been on during the day time for the last week or so and it set me thinking about how street lights actually work.

I assumed that they use some sort of automatic system, either a timer to know when to turn on and off, or a light detector to turn them on when it's dark and off when it's light.

Does anyone know which system we use here in NZ?

And why would all the lights in my street (about four or five lights) be on during the day? If the lights had their own system then I could understand one or maybe two failing and turning the light on during the day. But for all of them to be on says that they share a system.

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#923678 29-Oct-2013 17:09

I think it's some kind of ripple control system like what is used to remotely switch HW cylinders off during peak demand.

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michaelmurfy

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#923679 29-Oct-2013 17:10

Depending on where you are it could be using one of 2 things:

1) Ripple Control - your local electricity supplier injects a signal down the line which turns streetlights on or off, this is normally generated by a big motor like [this]
2) Light Sensors - used in places where ripple control doesn't control the lights.

If the streetlight has been on for quite a while it's likely got a faulty light sensor, you should ring up the council and report it.

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ubergeeknz

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#923680 29-Oct-2013 17:11

It just means someone forgot to set the switch to "More Magic"

MurrayM

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#923681 29-Oct-2013 17:13

ubergeeknz: It just means someone forgot to set the switch to "More Magic"

When I was a kid I used to think that someone had a job to turn the street lights on and off. They would sit in an office somewhere and control all the lights in Auckland!

sbiddle

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#923682 29-Oct-2013 17:14

michaelmurfy:
If the streetlight has been on for quite a while it's likely got a faulty light sensor, you should ring up the council and report it.

Streetlight circuits normally cover quite large areas. Assuming it's never going off it could be a fault, or could be maintenance being done elsewhere, ie looking for blown bulbs and replacing them.

MurrayM

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#923683 29-Oct-2013 17:15

I'm on Auckland's North Shore.

So with ripple control would they control whole suburbs with a single motor, or would they need one motor for every, say, 100 lights?

Just wondering why it only affected all the lights in my street and none of the surrounding streets.

gregmcc

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#923689 29-Oct-2013 17:35

MurrayM: I'm on Auckland's North Shore.

So with ripple control would they control whole suburbs with a single motor, or would they need one motor for every, say, 100 lights?

Just wondering why it only affected all the lights in my street and none of the surrounding streets.

Yes it is possible to control a whole suburb, but a single failure could me a whole suburb without street lights, its eaiser to use a number of more local daylight switches, that way when it actually gets dark they turn on, when it is actually light enough they turn off, no other form of control is needed.

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MurrayM

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#923693 29-Oct-2013 17:38

gregmcc: Yes it is possible to control a whole suburb, but a single failure could me a whole suburb without street lights, its eaiser to use a number of more local daylight switches, that way when it actually gets dark they turn on, when it is actually light enough they turn off, no other form of control is needed.

So these ripple control motors would be located all over the place, in some sort of street-side cabinet? Or would the motors be housed centrally with lines going out to groups of street lights?

gregmcc

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#923701 29-Oct-2013 17:55

The ripple control (for hot water cylinders) will be located at substations and if it is used for street lighting control also at the substation, but usually street lights use the daylight switches, these are more unobtrusive and can be located in more local street side cabinets, they may control as little as one light or several streets, that way if one fails to come on or go off it's not a too major problem

SaltyNZ

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#923713 29-Oct-2013 18:33

MurrayM:
ubergeeknz: It just means someone forgot to set the switch to "More Magic"

When I was a kid I used to think that someone had a job to turn the street lights on and off. They would sit in an office somewhere and control all the lights in Auckland!

Ubergeeknz of course refers to this.

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SaltyNZ

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#923720 29-Oct-2013 18:41

When I did my electrical engineering degree, we had to do two semesters of the TAFE electrician's course practicals. We were a little annoyed to find that they had changed the rules the year before: the class one year senior to us could actually get their ticket on top of their degree. We would have had to to do an apprenticeship as well. But I digress...

One Thursday morning we walked into the practical room and someone turned on the lights as they walked in. A second or so after that, one of the starter caps burned out with a little bit of fireworks and then the lights went off.

In our practical class we had not only we Electrical Engineering students, but also the Bachelor of Technology students, whom we often described as 'electrical engineering for people who can't count.'

One of the B. Tech students, E, says 'Hey, why did the lights go out?'
Salty: 'Oh, the starter cap over there blew.'
E: 'Yeah, but why did the lights go out?'
Salty (frowning): '...Because the fuse blew?'
E: 'Yeah, but why did the *other* lights go out?'
Salty, pointing at the switchboard and speaking slooooowly: 'E, do you see that box on the wall over there?'
E: 'Yeah'
Salty: 'Well, inside that box is a little man. When one of the lights goes out because of a problem, he turns off all the other lights too.'
E: ಠ_ಠ

/CSB

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Geektastic

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#923724 29-Oct-2013 18:46

You have a council that provides street lighting? Nice.

Jaxson

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#923726 29-Oct-2013 18:49

Yeah just to help the original poster, street lights are grouped into circuits and there is an on/off switch that controls that group of lights. The switch to each group of lights can be one of a range of options, such as light sensors, timers or via the output of a central control system. Most street lights are lights only, they don't have daylight sensors on each lamp. There will be a switching point somewhere along the circuit.

Timers are bad as the on/off times change rapidly throughout the year, not just with day light savings either. It gets dark at different times as the seasons change.

So anyway, just thought I'd try to clear that one up for you. That's what they are all on at the same time, because they are grouped together and all switched on or off at one place. If they're on during the day, it's either a switch fault, a sensor fault or on for a reason, for fault finding purposes etc. It's usually one of those scenarios.

josephhinvest

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#923738 29-Oct-2013 18:55

I remember when I was young we lived in a small culdesac on the shore, which had one streetlight, with an optical sensor. So when we were Spotlight or Go Home Stay Home at night, you could stand and shine your torch into the sensor for a minute or two and the streetlight would turn off! Great fun.

Cheers,
Joseph

wasabi2k

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#923756 29-Oct-2013 19:35

There is a set of equipment at a switching station - there is a standard 42U rack there with a keypad and display. You can key a code into that to turn specific zones off and on. It makes an awesome thunking sound when you do it.

The control of this is also tied into the SCADA system - this is operated by a control room which can turn zones on and off as required from a computer screen.

The automatic turning off and on is controlled by a combination of light sensors and clocks - which adjust for daylight savings. The light sensors are in various locations around the place, not on every streetlight. Time is synchronised to a GPS NTP source.

I am sure I'm missing some details but that's all I can remember.

source: I worked on the SCADA system and got the tour of the equipment

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