y) between the reflectance of 8 to 14 standard colors as illuminated by the test light and a correlated light source of equal luminance and a flat, smooth emission profile, after chromatic adaptation to each light.
the warm/cool contrast and the opponent dimensions
relative visual response to illuminants A and D65
Fluorescent lights generally have reduced CRIs. They emit a broken spectrum that has an undulating shape across the spectrum and contains very high, sharp spikes at specific wavelengths (right). These hardly match the smoothly curving, domed curve of a blackbody spectrum, and the surface color reflectances at the "spike" wavelengths are grossly inflated in the total color appearance, producing a greenish or bluish cast that has an especially dulling effect on warm colors. "Cool white" fluorescent lights have a CRI from 65 to 85, "daylight" fluorescents around 80, and "warm white" fluorescents from 55 to 75. Metal halide bulbs range from the mid 60's to the mid 90's; and those beloved sodium vapor lamps, which transform all colors into a yellowish, cadaverous gray, have CRIs close to zero.
The best light sources are those that make all colors all hues at all levels of chroma and lightness appear "natural" or completely untinted. These are broadband, smooth spectral power distributions with chromaticities close to the daylight spectral path: incandescent lights (tungsten or halogen lights), propane lanterns, carbon or xenon arc lamps, burning magnesium. Incandescent or tungsten halogen bulbs all have a CRI of 100 and deliver a "true" color balance.
How can a light source that has an off white or "warm" color (such as a 120 watt incandescent bulb at 2860°K) still have a CRI of 100? As long as the light approximates a high temperature blackbody source, it generates light across the entire spectral range without spikes or gaps, and our eyes will be able to preserve the perception of "white" illumination by chromatic adaptation. That adaptation is the origin and principal basis of our warm/cool color sensitivity.
The Univerity of Nebraska-Lincoln hosts a simple blackbody curve simulator that calculates the emittance spectrum and peak energy for a blackbody from 3000°K to 25,000°K. Mitchell Charity has posted several useful pages on blackbody colors with links to additional resources.
the warm/cool contrast in paints
I have explained why lightness and chroma are responsible for the "advancing" (spatial depth) or "arousing" (mood) effects attributed to warm colors, and why the warm/cool contrast is a visual adaptation to changes in natural light. The last piece of the puzzle is to explain how the warm/cool contrast appears through our perception of surface colors such as paints.
Unfortunately no modern color model represents the warm/cool contrast as a distinct dimension of color perception, so the answer has to expressed in terms of paint reflectance curves and their colormaking attributes.
spectral emission curve of a fluorescent "daylight" bulb with a CCT of 4370°K
from Wyszecki & Stiles (1982)
Green Is Neither Warm Nor Cool. If we compare the visible spectrum to the daylight color spectrum shown above, we immediately notice a glaring omission: there is no "green" in the daylight color spectrum.
The reason is that most noon daylight phases, with CCTs between 5800°K and 5000°K, are actually slightly green in hue (right, and above). Green is also the range of maximum reflectance in chlorophyll (which absorbs only short and long wavelength light) and therefore is the color of landscape vegetation. Green is not perceived as a sky color.
This green hue is briefly visible in the positive afterimage caused by glancing at the sun or staring at its reflection in a dark glass or water; but we are adapted to accept it as "white" light. (The afternoon sun appears yellow because atmospheric filtering has reduced its brightness and begun to shift the color toward red.)
As a result green is neither warm nor cool, because it is (at high luminance) associated with solar light and our perception of the white point or an equal balance