Why must a camera be light-tight when a photograph is being taken?

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Diagram showing the negative-positive photographic process: a scene is captured on film in a camera, developed into a negative, projected onto paper with an enlarger, and developed again to produce a positive print. — technology of photography Figure 1: Sequence of negative–positive process, from the photographing of the original scene to enlarged print (see text).

A camera must be light-tight to ensure that the only light reaching the image-recording medium—such as a sensitized film, plate, or digital sensor—is the light specifically admitted through the lens.1

The camera box serves the essential purpose of holding and protecting this recording medium from all extraneous light. Because the technology of photography relies on precisely controlling the amount of light that exposes the medium, any light leaking into the camera from other sources would interfere with the image, leading to overexposure or unwanted artifacts. By maintaining a light-tight environment, the camera ensures that the shutter and aperture can accurately regulate the exposure, allowing the lens to project a controlled, sharp image onto the image plane.12