The light measurement (English (incident) light metering ) is a term used in photographic technology and describes a method of metering . It is the direct opposite of object measurement . Since, in contrast to this, the incident light cannot be falsified by the different reflection values of the object, it is often much more precise than this - but it is also more complex and therefore less practical in dynamic recording situations such as reportage or snapshots.
Light measurement is often used for portrait or fashion photos.
When measuring the light, the photographer or cameraman uses a handheld exposure meter to determine the illuminance directly on the object. In contrast to the object measurement, which takes place in front of the object , the photographer stands directly on the object; alternatively, he can also measure in a lighting situation that is comparable to the motif and as identical as possible. The measuring head of the exposure meter points in the direction of the camera.
To measure light, a diffuser (often in the form of a small milky hemisphere, the dome ) must be attached in front of the light meter's measuring head . This normally has a transmission value of 18%, which corresponds to the reflection value of neutral gray.
A suitable diffuser is usually supplied with the light meter; only very simple handheld light meters do not have a diffuser.
For light measurement without a diffuser, see substitute measurement .
Polar bears are supposed to be photographed on a glacier on a clear day. When measuring the object, the exposure measurement would be falsified by the white of the object, which deviates significantly from neutral gray (high reflection value), the film would be underexposed, and even significantly due to the high light intensity. By measuring light, the reflection value of the object is eliminated as an error factor and the exposure is measured correctly, so the film can be exposed correctly.
Since in this case a light measurement directly on the object is not practical, the light can be measured in a lighting situation comparable to the object; in the situation described, on a shadowless glacier, also directly at the point of view. Outdoors, the brightness on the subject often corresponds to the brightness at the location where the picture is taken, so that the photographer only has to turn 180 ° to determine the brightness on the subject.
Two measurements. If the subject is partly in the light and in the shadow, the exposure can be controlled by the photographer taking two light measurements on the object: once in the shadow and once in the light. The exposure can now take place according to the average value of both measurements or according to the photographer's idea.