Colorimetric data as revised by Judd can be transformed to Konig funda
mentals L, M, S, representative of the long-(LWS), middle-(MWS), and s
hort-(SWS) wave-length sensitive cone spectral sensitivities. The fund
amentals are normalized so that two cone types, M and L, sum to the lu
minous efficiency function, Y-J. The height of the S fundamental is un
defined in this transformation. A constant luminance chromaticity plan
e can be derived by calculating L/Y-J and S/Y-J, with the area of S se
t equal to that of Y-J. This chromaticity space is convenient for calc
ulations of real stimuli. The axes of this space, when adjusted to ref
lect cone adaptation to the equal-energy spectrum have been shown to m
atch the null axes of the major retino-cortical processing streams. Th
e relative cone troland chromaticities can be multiplied by the retina
l illuminance level to give L, M, and S trolands. In this metric, chro
maticity data can be plotted as threshold-vs.-illuminance functions. C
one excitation is derived from cone trolands, by dividing by the maxim
al sensitivity of the fundamentals. Cone excitation units are used to
derive models of retinal processing. The cone quantal excitation rate
is a scaled version of the cone excitation. (C) 1996 John Wiley & Sons
, Inc.