Is there such a thing as an "eye" sensor that detects light instead of darkness?

Question

I want to add a light to the bathroom that automatically comes on when you flip the switch to the main light (without rewiring the bathroom). Is there such a thing?

... like the nightlights that automatically come on when it's dark... but the opposite.
So that the light comes on with the main light.

Answer 1

Probably not, since once it turned on, it would keep itself on. It might also be difficult to adjust to compensate for ambient light.

Any home center should have a selection of motion-operated lights ranging from night lights to sensors that attach to a regular lamp. Might that be do the trick, since you're presumably always going to have a human in the bathroom when you want the light turned on?

Answer 2

I'm sure there is but whether it exists in a form which you can afford and install I doubt. Haven't seen one.