What is the name of the light sensor?

Question

Do it yourself

It is necessary to determine whether the light is on in the room or not (you do not need to determine the brightness, there is no natural light in the room) and signal this via WiFi (cutting to the wiring between the switch and the light bulb is not an option). What is the name of the sensor/device for this? I want to google and maybe buy.
As an option, options with a "solar battery" from a calculator, a smartphone with a camera, etc. loom in my head, but it's interesting to google whether there are more or less cultural ready-made solutions inexpensively.

Answer 1

Do you need a ready-made device that will detect the presence of lighting in the room and signal via WiFi? Or will you do everything yourself, and you only need a device to determine the lighting in the room?
If the first is rather a thread in the direction of gardeners to dig, then google "wifi light sensor". If the latter, then you need a photoresistor.