Quote Originally Posted by auld argonian View Post
. . . film of the period didn't respond very well to the red end of the spectrum . . .
Such film was called "orthochromatic" and was almost the only black-and-white film available until the late 1940's, when it began to be supplanted by "panchromatic" film. The latter was approximately as sensitive to the brightness of red as the human eye is. The advent of panchromatic film ended the era of red darkroom safelights.

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