LEDs as sensors, newbie needs help!

Charge transfer -adc module
I suspect I have seen a post on this somewhere here but I have searched here for "charge transfer " and "LED charge transfer " and "adc module " and the only thing that comes up is the above post.

I have done the same searches on DuckDuckGo and not seen anything I could directly associate with an LED or even a capacitor apart from Franklin flying a kite?

Would you please elaborate on this hopefully with a reference point so I can see what you are talking about.