I have been using MAX/MSP to control LED lights through DMX (acronyms everywhere). In other words, using my computer as an interface to control lights with the sound of my flute playing. I wanted to close the circle (process my flute playing) with the lights, and for that, I used light sensors. With that system, I can make feedback loops between light and sound. I have made a few pieces with this already, and I have not exhausted the possibilities yet. This is going to keep me busy for a while.
On the video I am using photocells (photoresistors) to modify the sound. I haven them connected to the computer through an ESP32. The response of the sensor changes with the brightness of the light. At the same time, the lights are connected to the computer as well, so they respond to the sound.
I am using the microphone to create feedback with the transducer on the table, thus having two feedback loops at place (light/sound and mic/transducer).
In other projects I used an RGB sensor, which is a similar thing but has the possibility of understanding colors, which is very useful considering how much I have been using color-changing lights in the last few years.