Eclipses and perceived brightness

Factual Questions
1

Viewing the solar eclipse yesterday, I was struck by how little the day seemed to darken, even when the sun was ~85% occluded. It’s been a long time since I paid attention to an eclipse, and I expected a sort of twilight. I think I was remembering a total eclipse from when I was much younger.

I’m pretty sure that the reason it seemed to get only a little bit darker instead of getting much darker is that perceived brightness isn’t linear, but I’m trying to find a scale for that, and not having much luck. I found a few references to this effect on some lighting fora, but they’re not very clear, and seem to talk about resolution of changes in brightness rather than an absolute scale. Can someone point me to a reference that shows that 15% of full solar light should seem to be about 80% (or whatever it is) as bright?

2

I can’t point to any factual studies, but consider how your eyes adapt to evening light. If you’re working outdoors, it usually still seems fairly light well after sunset, but if you then go indoors and turn the lights on, it looks very dark outdoors all of a sudden. In other eclipse threads I’ve pointed out how you don’t get a real noticeable darkness until very close to the moment of totality. The light fades out pretty gradually during the partial phases, so your eyes can adapt easily and you don’t notice it.