im making sofware that generates pretty html calendars displaying this in normal almanac type forms. I'm trying to make it easier to see "at glance" which nights are darkest, or when the darkness lasts longest, for things like astro-photography... or which nights are best lit for hunting.

The data is the easy part. Deciding how to show it in a way that makes sense and doesnt require effort to decode, that's hard. The sublime ease with which we read conventional calendars is amazing.