How Does a Light-Detecting Book Light Circuit Work?

[Poincare1]

Firstly, the book light works fine. I'm also attaching a circuit diagram.


I don't really understand why the emitter of the transmitter (its marked with an E) takes in the current. Could someone explain to me how this circuit works?

 

[MATLABdude]

Firstly, the book light works fine. I'm also attaching a circuit diagram.


I don't really understand why the emitter of the transmitter (its marked with an E) takes in the current. Could someone explain to me how this circuit works?

There's a circuit diagram?