Lichtwert

Lichtwert, literally “light value,” is a logarithmic unit used in photography to express the brightness of a scene as it relates to exposure. In German-language photography and film technology, it is the term most often used for what is called Exposure Value (EV) in English. The Lichtwert reflects how much light is available for a correct exposure and depends on the aperture, shutter time, and the reference ISO.

The standard relation for Lichtwert is LW = log2(N^2 / t) when the reference ISO is 100, where N is the f-number (aperture) and t is the exposure time in seconds. When the camera or meter uses an ISO other than 100, the exposure value at that ISO can be expressed as EV = LW − log2(ISO/100). In practice, Lichtwert values on a light meter indicate the amount of light that would produce a proper exposure at ISO 100.

Usage and examples: Light meters or camera manuals in German-speaking contexts display LW values to guide exposure planning. For example, with an aperture of f/8 and a shutter speed of 1/60 s, LW ≈ log2(64 / 0.0167) ≈ 12. A bright sunny scene might yield LW in the mid to high teens at ISO 100.

Differences and context: Lichtwert is essentially the German term for exposure value with ISO 100 as reference. In modern international usage, EV is more common, and devices may display EV values or ISO-adjusted equivalents. Nevertheless, Lichtwert remains a standard term in German photography literature and older equipment.