Abstract

A rationale and methodology is developed which allows the systematic and definitive testing of a scalar luminance-additivity law (Abney’s law) within any photometric system which operationally defines luminance equality. For example, under the postulate that all stimuli have the same luminance at absolute threshold, the following inference is made: If a subthreshold field of λ_c is set so that it is some proportion p of the energy required to bring itself to a just-visible level, then the energy of any other wavelength λ_i which must be added to the same λ_c subthreshold field in order to bring the λ_c+λ_i mixture to threshold should be the proportion 1−p of the energy required to bring λ_i to threshold when no mixing is involved.

In an experiment concerned with such mixtures, it is found that a scalar additivity law does not even approximate the facts of luminance addition at threshold, with complete failure of additivity being apparent under some conditions. Moreover, the data suggest the presence of an inhibitory effect in which a light is less visible when combined with subthreshold light of a different wavelength than when presented alone.

© 1965 Optical Society of America

Some Comparisons between Foveal Spectral Sensitivity Data Obtained at High Brightness and Absolute Threshold

H. G. Sperling and W. G. Lewis
J. Opt. Soc. Am. 49(10) 983-989 (1959)

Heterochromatic additivity, foveal spectral sensitivity, and a new color model*

Sherman L. Guth and Howard R. Lodge
J. Opt. Soc. Am. 63(4) 450-462 (1973)

Effects of Continuously and Discontinuously Moving Stimuli on the Luminance Threshold of a Stationary Stimulus

S. M. Luria
J. Opt. Soc. Am. 55(4) 418-425 (1965)

Relation of Increment Thresholds to Brightness and Luminance*

Tom N. Cornsweet and Davida Y. Teller
J. Opt. Soc. Am. 55(10) 1303-1308 (1965)

Intensity–Time Relationship at Threshold for Spectral Stimuli in Human Vision*

H. G. Sperling and C. L. Jolliffe
J. Opt. Soc. Am. 55(2) 191-199 (1965)