The Derrington, Krauskopf and Lennie (1984) color space is based on the Macleod-Boynton (1979) chromaticity diagram. Colors are represented in 3 dimensions using spherical coordinates that specify the elevation from the isoluminant plane, the azimuth (the hue) and the contrast (as a fraction of the maximal modulations along the cardinal axes of the space).

It’s easier for me to think of a color in **cartesian** DKL coordinates with the dimensions:

- Luminance or L+M, sum of L and M cone response
- L-M, difference of L and M cone response
- S-(L+M), S cone responses minus sum of L and M cone response

The three classes of cones respond a bit to almost all colors, but some reds excite L cones the most, some greens M cones the most, and some blues S cones the most.

I’ve created the below movie (thanks Jon Peirce and PsychoPy) to show successive equiluminant slices of DKL color space, plotted with cartesian coordinates. These render correctly on my CRT screen, but the colors will be distorted on any other screen. Nevertheless it helps you get a feel for the gamut (colors that can be represented) of a typical CRT at each luminance, where -1 is the minimum luminance of the CRT and +1 is its maximum. The letters R,G,B and accompanying numbers show the coordinates of the phosphors (each gun turned on by itself).

Derrington AM, Krauskopf J, & Lennie P (1984). Chromatic mechanisms in lateral geniculate nucleus of macaque. The Journal of physiology, 357, 241-65 PMID: 6512691

MacLeod DI, & Boynton RM (1979). Chromaticity diagram showing cone excitation by stimuli of equal luminance. Journal of the Optical Society of America, 69 (8), 1183-6 PMID: 490231