This dark activated switch can trigger a relay to operate an AC lamp at Sunset ... of the house when the occupants are out of station. The circuit utilizes the light sensing property of LDR to ...

Impulse relay turns on with an electrical impulse at the control input and turns off again with another impulse.

Although the author used a “modified” laser diode lifted from his cheap laser pointer, you can use any (suitable) readymade laser diode module ... of this circuit section is a 5mm photoresistor ...