"The operating principle of the optocoupler is fairly simple. As the intensity of the LED varies, so does the internal resistance of the LDR (resistance decreases with increasing light).
I've used them in audio.
So have I -- AGC.
There are versions with lamps and with LEDs, with a photocell as the output.
Ok, actually it should be even easier than I thought. I just need to increase the intensity of the LED and with my DSO (Digital Storage Scope) display the output (and save it to file.)
Sounds about right?
Do It !