Different types of switches?

Question

is there a switch that could be put in a circuit that breaks the circuit if there is no light? if so what is it called

Answer 1

a photocell

Answer 2

a photo diode changes resistance with light, it does not "break the circuit"

A photodiode puts out voltage with light, it also does not "break the circuit"

You can use a photodiode to drive a sensitive relay and use the relay contact to close when there is light.

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Answer 3

Photo sensitive diode - it works much like an LED in reverse. If there is light on the diode, it allows current to pass. This is what is used in solar panels to produce electricity.