Peg, sounds like (actually, no sounds), you have a winner!
Have you ever played with Room EQ Wizard?
It’s a free audio analysis package that runs on Windows, Mac, or Linux.
40 years ago I could have charged just to let other audio geeks watch it do tricks.
I used to look at PWM before I found better software and eventually a more modern O-Scope.
I did a POST about it a few years back:
I’m sure you’ve got a mike or two lying around.
It would be interesting to see if you could get a frequency plot from you light by holding a mike against it.