In article ,
The Wanderer writes:
On Fri, 1 Apr 2005 01:29:52 +0000 (UTC), Andrew Gabriel wrote:

It's probably just timer driven, but using an automatic daylight
adjustment for the 'on' time, which is a standard feature of
timeswitches which used to be used before photocells took over.
It sounds like the timeswitch has lost 2½ hours. They usually
had a spring backup to cover powercuts, but that will run down
eventually.

Err, no, there are such things as 1/2 night controllers......

Which is exactly what I described in the text you quoted in full.
I used to have a mechanical one (could be set for 1/2 night, full
night, and a few other plans). Quite a remarkable piece of
mechanical engineering. Mine didn't have the spring reserve option
fitted, but I believe streetlamp ones normally did.

There was also a chip which could do something similar developed
some ~30 years ago. It switches on at dusk and tries to switch off
at a fixed time. It does this by measuring the length of the dusk
to dawn period to estimate the time it gets dusk, and thus works
out how long the light needs to be on after dusk in order to switch
off at a fixed time. When reset following a power cut, the first
night it will leave the light on all night as it has no idea how
long the dusk to dawn period is. On subsequent nights, it will
have learned the dusk to dawn period and calculates when to switch
the light off. The learning would cover a few days of data so that
one dark afternoon would not throw it wildly off track. However,
this appeared on the schene just as councils were reconfiguring
all their streetlighting to run all night and converting from
expensive error prone daylight adjusting mechanical timeswitches
to cheap reliable photocells, so I'm not sure there was ever much
uptake of it. I bought one and played with it on a breadboard
layout, but I never deployed it in any finished design.

--
Andrew Gabriel