Thanks! She's actually indoors in a room, and the light source behind her is a lamp. There are other lights in the room, such as in front and behind her.I assume the "rain lines" running through her hair vertically are the watercolor drip interaction you described, I think that's probably my favorite feature of the painting overall. It really amplifies the sensation of her being backlit by the sun. I bet if you got them to run in the direction of the light it would be even moreso, not sure how much control you have over that.
Anyway, very cool, thanks for sharing.
Excellent artwork, but that's not Frank Fiegel. https://www.snopes.com/fact-check/frank-rocky-fiegel-popeye/