Variation of photographic sensitivity with different light sources

Abstract

The variation of photographic sensitivity (as measured by the index 10/E m ) with different sources of light of equal visual intensity, but having different distributions of energy, was experimentally obtained. Ordinary, orthochromatic, and three new fast panchromatic plates were investigated. Distinction was made between two types of sensitivity comparisons. Thus it was found that: first, the ratio of the sensitivity of any one of the panchromatic plates to that of the ordinary plate was greater with incandescent lighting than when “sunlight” was used, and second, in all cases the panchromatic plates were less sensitive to incandescent lighting than to “sunlight.” Approximate factors are included (for the particular emulsions studied) by which visual exposure meter readings should be multiplied when certain types of illuminants are encountered.