Abstract
The experiments in which the strengths of pattern and of fusion differing in kind from brightness were used as measures indicated that the visual system could distinguish between illuminance and reflectance. From this result and an observation of gray papers by a microscope, it is assumed that luminance has two aspects, one refers to the macroscopic density of photons and another to the proportion of the reflected microscopic areas to the absorbed microscopic areas so that brightness constancy occurs in relation to each of the patterns of the various sizes from a macroscopic pattern visible to the naked eye to a microscopic pattern not visible. It is also mentioned that the strength of fusion is rare but promising as a measure for analyzing brightness.
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