You need to be discharging the capacitor somehow; I suppose it was meant to measure the charge, even then measuring the cut off of the sine is not hard. It's ju

You need to be discharging the capacitor somehow; I suppose it was meant to measure the charge, even then measuring the cut off of the sine is not hard. It's just all retrofitting design - led into incandescent bulbs, LED drivers into sine cutters - all to preserve the existing lighting fixture. I have some near ceiling lights that allow dimming via a remote control (infra red or 433MHz) or fast switching on/off (remembering their state afterwards). There are other ways to communicate, e.g. using the zero cross - the dimmer can send whatever signal to the lights downstream - the latter would read it and set the brightness.