For as long as people have been taking photos, there has been a need to determine how bright a scene is. Any method of recording light can only work in a relatively narrow band without over or under exposing the image. To find the correct exposure that will record the image without over or under exposing it too much, photographers need to know how bright the scene is. An extremely talented photographer may be able to guess a near-enough exposure, but a light meter is a far more accurate and convenient way to do it. - Kelly W.