“You do not have to sit outside in the dark. If, however, you want to look at the stars, you will find that darkness is necessary. But the stars neither require nor demand it.”

Widely attributed to Ralph Waldo Emerson on the internet; however, a presumably definitive source of Emerson's works at http://www.rwe.org fails to confirm any occurrence of this phrase across his works. This phrase is found in remarks attributed to Charles A. Beard in Arthur H. Secord, "Condensed History Lesson", Readers' Digest, February 1941, p. 20; but the origin has not been determined. Possibly confused with a passage in "Illusions" in which Emerson discusses his experience in the "Star Chamber": "our lamps were taken from us by the guide, and extinguished or put aside, and, on looking upwards, I saw or seemed to see the night heaven thick with stars glimmering more or less brightly over our heads, and even what seemed a comet flaming among them. All the party were touched with astonishment and pleasure. Our musical friends sung with much feeling a pretty song, “The stars are in the quiet sky,” &c., and I sat down on the rocky floor to enjoy the serene picture. Some crystal specks in the black ceiling high overhead, reflecting the light of a half–hid lamp, yielded this magnificent effect."
Misattributed

Variant: Only in the darkness can you see the stars.
Context: But I know, somehow, that only when it is dark enough, can you see the stars.

Heechee Rendezvous (1984)

Frankenstein, trying to explain to his fiancee why he experiments the way he does
Frankenstein (1931)

Source: Inferno

Source: Queen Margot, or Marguerite de Valois

Spaceballs