Information capacity of radiation detectors and of light

Data are presented on the information capacity and on the information efficiency of a beam of light and of several kinds of detectors including heat detectors, a multiplier phototube, an image orthicon, four photographic films, and human vision. The information efficiency is the information capacity divided by the number of photons that are needed to achieve the capacity, and is measured in bits per photon. The photographic films are discussed in separate sections from two points of view: that of maximizing the information capacity in bits/cm2, and that of maximizing the information efficiency. The other detectors and the beam of light are discussed only from the point of view of maximizing the information efficiency, because there is no upper bound to the information capacity that is related to practical use. The paper is primarily a review of the results of four previously published papers, but some new material is included: The results in Tables I and II on the information capacity of a beam of light are more extensive and more accurate than those previously published, and an explicit proof is given for the fact that it is not necessary to employ a radiation signal having spatial structure to obtain the greatest information efficiency with an image-transducing detector; a time varying radiation signal incident at a single point of the responsive surface is sufficient to achieve the maximum possible information efficiency.