Hopper said the painting "was suggested by a restaurant on Greenwich Avenue where two streets meet. I simplified the scene a great deal and made the restaurant bigger." Hopper posed for the two men in a mirror and wife Jo for the girl. Nighthawks was probably Hopper’s most ambitious essay in capturing the night-time effects of manmade light. This interior light comes from more than a single lightbulb, with the result that multiple shadows are cast, and some spots are brighter than others as a consequence of being lit from more than one angle. Light was the most powerful and personal of Hopper's expressive means. He used it as an active element in his paintings to model forms, define the time of day, establish a mood, and create pictorial drama by contrasting it with areas of shadow and darkness.
Hopper made many small sketches of concepts and details of his pictures before working on the final paintings. Many of the sketches for this painting still remain. To see the original : https://www.wikiart.org/en/edward-hopper/nighthawks