American Standards Association (ASA) was a scale used to indicate the light sensitivity, or speed, of photographic film. Higher ASA numbers signified greater sensitivity to light, with doubling the ASA number indicating twice the film speed. This standard allowed photographers to choose appropriate exposure settings for different lighting conditions and helped ensure consistent results across cameras and film types. Although the ASA system was widely used for much of the 20th century, it was replaced by the ISO scale in the 1980s, which combined ASA and DIN systems into a unified international standard. Understanding ASA provides historical context for film photography and the evolution of film speed ratings.