Change from light to sound.
Light that we see.
May be mixed with the audio signal.We normally can not detect it.
But this be Light Wave Receiver circuit can tell it, perform take sound signal from the light by modify from the light into pieces hear at a loudspeaker.
By the circuit uses LM741 , be IC op-amp the multi-purpose IC.
It use for enlarge sound signal , change the way Photo transistor into pieces give hear loudspeaker way well.
You can take the test light.
Screen color TV receivers, lighting, home lighting and so on.