The Medway Handyman wrote:
Hi All

Had a job today, lady recently moved in, hall light had packed up.

Turned out to be a faulty dawn to dusk sensor. White plastic thingy about
80mm long, 30mm dia with a male bayonet one & a female the other. Removed
it, Robert is your fathers brother. Got me thinking though!

How do these things work? I can see the logic of 'it's dark, switch on' but
how do they stay on?

I assume they have a photo cell of some kind? Why doesn't the light coming
from the bulb trigger the sensor and turn the bulb off? Daylight would
trigger it and the bulb is much closer & brighter.

They turn off for .5 sec every half an hour or so, to see if it's still
dark.