How Street Lamps Turn Themselves on and Off
An essay on how street lamps turn themselves on and off.
How do street lamps turn themselves on and off with the sun? There are millions of street lamps across the world, and they are turned on and off every morning and evening. One of the earliest ways of doing this was to use time switches.
Time switches operate a section of lights in a neighbourhood, and turn literally is a switch that turns on and off at certain times. But the sun doesn’t set and rise at the same time everyday, so how do they have season changes? To overcome this problem it is arranged by a mechanical device which adjusts the ‘On’ and ‘Off’ tappets according to the month.
The more common time of street lighting systems is a photoelectric control unit, “PECU”, which is a switch controlling the supply of electricity to the lamps. In the PECU unit is a photocell containing a light-sensitive compound. When the sun is up, the light falls onto the photocell causing the electrons to flow from atom to atom, conducting electricity to the switch and therefore turning it off. When the sun is down, there is no light and so therefore the electrons are unable to move turning the light on. The only problem with the system is that it depends on the weather conditions so it may be combined with time switches in the future.
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10 Responses to “How Street Lamps Turn Themselves on and Off”
On May 5, 2009 at 12:26 am
Great work!! Very interesting read.
On May 5, 2009 at 8:34 pm
Interesting, thanks for sharing*
Blessings.
Sincerely,
-Liane Schmidt.
On May 7, 2009 at 11:34 am
Very cool. I never knew this.
On May 12, 2009 at 4:00 pm
Great informative article!
On May 13, 2009 at 4:37 pm
i found this most interesting. i have some garden lights that use solar power during the day; they absorb it and then at nightm, they illumin. so it’s fascinating to know that this was used since vicotian times. i had never heard of PECU either until now. this was one very good article. well done!!
On May 14, 2009 at 1:33 pm
Great article!
On May 14, 2009 at 7:15 pm
Nice one..
On May 21, 2009 at 9:17 pm
So your saying my idea about the gnomes is wrong?
Thanks,
Clay
On May 29, 2009 at 3:45 pm
This was very interesting to read. I always wondered how they changed the street lights due to seasons.
Thanks for posting!
On July 1, 2009 at 6:33 am
This is so interesting. Great write!
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