I understand the difference between realism and imagination, but my personal opinion (and that and 50 cents might get me a cheap cup of coffee) is that even imaginative painting shouldn't break the laws of nature without an adequate explanation. And three distinct light sources in the sky in an open-air painting is (again in my opinion) cheating, unless it's the Second Coming or something. This, on the other hand, is incredibly dramatic but still playing fair (courtesy of Thomas Cole again):
Not three but FOUR light sources - but he explains them all: sun, moon, fire, and . . . volcano!!!