my feeling is that the "total ambient light" changes extremely rapidly for the first and last hour (or even 45mins) of each day and hardly any at all (from a "noticeable" perspective) the rest of the day.
Likewise when you fade a led up from zero, most of the perceived change in brightness happens between zero and 125 (8bit resolution). Because persistence of vision, it is harder to notice a change in brightness as the PWM goes above 125 towards 255.
Your first point is quite valid, I am probably overthinking the whole thing by trying to create a curve that is noticeable in the sense that you would perceive the initial rise in brightness as brighter than it is. To me our eyes react more sensitively to brightness different than dimness. If the observer was present since the sunrise it would seem to gain brightness quickly or walking in to the simulation at 10am it might seem already at full brightness as there is no frame for reference, whereas as the light dims it seems less obvious until a certain point. Like when you are rushing to get a project done outside before dark and don't realize how dark it is until you go inside the house and come back out, lol.
As far as your second point, I guess I didn't think of the perceived change in brightness as being non linear on the PWM side as well
So I am stuck trying to weigh the variables between trying to provide a noticeable difference in brightness without having to observe for large amounts of time and providing adequate light for healthy growth during the photo-period without stressing the plants or fish by blasting them with full light for the whole photo-period. While at the same time, showing that you can provide a healthier photo-period with less or the least amount of light. I figured I would have to do some extensive testing of different fade curves to get the best result which is why it originally made sense to me to use a matrix that I could plug values into the sketch as well as trying to write code to set simple parameters like on and off time by just using push buttons or a touch screen