Ah sorry. Yes, in that context, my understanding of “well lit” would be making the images vivid, so they are clear and impactful - it could be with light or something else depending on your “visualisation style” (for me images are very burry, I just know what’s there because I build them with “internal logic” and a dash of emotion). I don’t recognize people because of detailed visual cues, only very basic ones, but rather I have a sense of their personality (I put a character in a locus/situation and they react a certain way… for example, Kyou is often angry and suspicious).
Also a photographer would tell you that light is very important (good light makes everything look beautiful, bad light is… really hard to work with). I guess in that sense it is for me: I prefer to choose “pretty and peaceful” places for my memory palace, for example.
(All of this is pure opinion and to take with a grain of salt, because I didn’t actually read that book)