The Flash Photography Field Guide

Intensity

Intensity is the measure of how bright light is. In photographic terms, we usually think of this in terms of EVs, or more usually, the ƒ-stop or aperture it requires for the scene to be recorded accurately at a given ISO or shutter speed.

For many years—certainly before the advent of digital photography with its instant feedback—the intensity of light was a crucially important factor. Photographers would spend a long time metering the light with handheld meters, or using their experience of their own camera and its TTL metering system, plus the sensitivity of the film emulsion they were using, to make a judgment on what camera settings to use. Then they had to wait for the film to be processed to see if they had judged it accurately. ...