Log e refers to the logarithmic value (to the base 10) of the relative brightness that a photographic film is exposed to during sensitometric testing. It is used to quantify the film's response to light and to create characteristic curves that show how density changes with exposure.
Understanding Log e is important for photographers, lab technicians, and imaging scientists who need to evaluate film performance, exposure latitude, and tonal response. By analysing these logarithmic values, professionals can make informed decisions about exposure, development, and print quality for both black-and-white and colour photographic processes.