There's a great rumination of the mid-century pulp-gothic romance at the My Romance Story blog. It's no small wonder the genre came back into fashion in the 60s during the battleground of the modern feminist movement; the classic storyline of very flawed and/or 'evil' men victimizing or constraining a clearheaded heroine has obvious commentaries of the social climate of the time.
I've recently been interested in the depictions of the genre; I see many, many old paperbacks while bookscouting. In the Romance Story blog, the writer claims it is somewhat of a misnomer that most or all such novels sported a woman -in-nightgown fleeing from an old mansion with one window illuminated. She says very few did, but I have literally seen hundreds of such covers, both in person and on the web. Even with the ones that strayed from this exact cookie-cutter template, the covers still contained the elements of such.
With some covers, a woman may not be fleeing in a nightgown, but confidently poised in evening wear outside a large house. If there is no light in a window, there is a huge full moon as light source, or she may be carrying a candle. But, there are almost always the 3 elements of house, light, woman. Sometimes men are present, and sometimes the scene even takes place indoors, or immediately in front of the house. In these last 2 cases, the woman is usually in dire straights, either being attacked, or slumped over, post attack.
I suppose it's a rather straightforward and easy reading: women being oppressed somehow by a man. But maybe more thoughtfully, as we see with the art, by a huge, looming, antiquated house. This carries obvious ideas that were at the forefront in the 60s--women getting out of their houses and into the working world. There are also ideas of family life here, and probably can be seen to symbolize all the dynamics and changes that were going on regarding motherhood, birth control, divorce, etc. The ubiquitous single light source in the scene can be seen both emphasize that something drastic has taken place, and to light a path.