@harvey, ok.. one detail I didn't include is that the photocells (the resistor part of the OCs) are not in series. The LEDs are in series (on a 10 volt loop). But the photocell-sides are sprinkled into various parts of the clean and dirty circuits to restrict or permit the flow of signal. They are most definitely not in isolated series.
Then you'll get the resistance changed by whatever the parallel connections happen to be. Still ought to tell you a bit.
