Interesting that these maps are always binary: light or dark, when the intensity of light varies based on how high the sun is in the sky. Is there a version of this map that takes that into account?
The page could be modified to present a gradient, since it only requires calculating the sun's altitude and solar time, which is not that complicated.
Meaning: you get full visual acuity with just a little light. Further increases often don't even register.
In numbers: typical overcast daylight is around 1,000 lux. Full sunlight is above 100,000 lux.
e.g. https://www.nrel.gov/gis/images/solar/solar_ghi_2018_usa_sca... but on the daily.