Light measurement.
Another newly used method is called light measurement or direct light measurement, while the former is called, by contrast, object measurement. That's what light measurement is all about, that a diffuser is placed in front of the instrument, which comes in different varieties and is held in front of the subject of the photo facing the camera. The transparency of the glass should be selected in such a way, so that the instrument pointer again points "correctly". Light measurement is therefore independent of the reflection coefficient of the object of the photo and in many cases leads to more "objective" indications than the measurement of the object. We can use it to replace the gray table method, which we might call the indirect measurement of light. This method is also applicable to more extensive motifs, to check the uniformity of illumination, which we cannot assess accurately by eye.
Modern, well-equipped film or photographic ateliers should also have lux meters, which are adapted to check illumination and general light intensity better than exposure meters. The light intensity value measured in the plane of the object is approx. 10.000 lux leads, for example, to the Vioosek irradiation., at the aperture 5,6 on color films with a sensitivity corresponding to 16°DIN. We haven't come to the end of our considerations yet. Using reversible color films, which we are now almost exclusively switching to, light meter correction is still required. We have to reckon with two cases of deviations, which so far concerned basically black and white materials with one difference, that reversible films, due to their modest range of usable exposures, react much more strongly to it.