Quote:
Originally Posted by Lancs Lad
I wonder how much electricity was consumed to run every individual timeswitch clock motor in every individual lamp column in every town, 24 hours a day?
Can you imagine! It must have mounted up....! I'm amazed the 1970s National Grid coped with it!
No wonder dusk/dawn photocells were adopted so readily
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It was not that great, the clocks were about 1 watt each. I don't know how many street lights there were, maybe a million (one for every 50 people) or perhaps two million street lights.
A million watts for time switches sounds a lot but is only 1 megawatt, large power stations of that era had several generators each of hundreds of megawatts capacity.
The early photocells used as much power as a time switch, but only in daylight, they consumed almost nothing at night.
The lamp was switched by the contacts of a thermal relay the heater of which was wired in series with a photocell.
In daylight the cell had a low resistance and most of the mains voltage would be across the heater of the thermal relay which would absorb a watt or so and keep the contacts open.
In darkness, the cell had a high resistance, passed virtually no current, and the relay cooled down, and thus closed the contacts and lit the lamp.
The modern all electronic photocells consume only a minute wattage.
Most streetlights are individually controlled, but in some areas group or central control is used, thereby saving costs, complications and losses at each street light, but adding to infrastructure costs.