A second DAC output controls a DIAC-based (X1) light-dimmer circuit. This dimmer circuit operates like any other light dimmer, except that the DAC controls it instead of a potentiometer. A photodiode ...

While the potentiometer will work, it will not provide automatic gain control; you can get that if you replace the potentiometer with a light bulb or a MOSFET. (View schematics for both ...