landscape surface colors.
blackbody and daylight color series
chromaticities of blackbody spectra under D65 adaptation; adapted from Charity (1997)
The major difference between the blackbody and daylight color series (when defined against a D65 "white" standard) is the visibly increased "green" component in the daylight colors from deep yellow to white, and from white through middle blue, which produces the noticeable yellow or cerulean tints around daylight colors close to white. These colors appear because "green" light shifts all "red" wavelengths toward yellow and all "blue" wavelengths toward blue green (cerulean).
chromaticities of CIE illuminants when eye is adapted to equal energy "white" (EE)
The yellow is visible in afternoon sunlight, especially in shafts of light into a darkened room, and in this range does not match the orange color of the blackbody spectrum. Ceruleans and very subtle greens are often visible in the sky close to the horizon, especially around sunset when the "violet" component of daylight is heavily filtered. At these times the low sky can appear to shade from a grayish deep yellow into scarlet (photo, right).
It is intriguing that green and rose hues (shown in the diagram immediately around the white point) appear in the afterimage colors of specular reflections, and commonly in the glint of iridescence or refraction colors in water and high altitude clouds near the sun, and the rose colors of dawn. These are subtle shifts in "white" color that are not within the daylight series of colors but are perpendicular to it (along a magenta/green dimension).
The artist can only marvel that the solar light and atmosphere can weave such a narrow chromaticity path and yet create so many landscape color changes and light contrasts. The color variations between dawn and sunset, or the sky seen from a seagoing ship and a mountain peak, or a desert sky before and after a cleansing cloudburst, or the light of spring and fall, or noon and twilight, or the colors of rainbow and iridescent sundog, are a source of abiding pleasure and fascination for landscape painters.
Lighting "Mood" Depends on Luminance. By focusing on the chromaticity of light we have ignored what is its most important attribute the intensity (illuminance or luminance) of the light source. The actual light color depends on light intensity, especially for chromaticities close to white, which means lights with the same CCT can have a very different visual impact depending on how bright they are.
The CCT does not literally stand for a specific color, only for a color tendency or color bias; the apparent color of a light will not necessarily match the "color" of its CCT. In addition, luminance affects our visual response. For objects at low to moderately high luminances, the blackbody color sequence seems to correspond to our experience of heated metals from the feeble red to yellow glow of heated iron. But metals heated above 1700°K appear to be a brilliant white, even though this "white" might be equivalent to an "orange" CCT of 2000°K or little more.
natural display of the
looking east during a Maine sunset
Solar light does not appear to be green, but either white or faintly yellow, for three reasons. First, our eyes easily adapt to the total daylight illumination as the standard for "white" light, and this adaptation is to a white point that resembles one of the CIE daylight illuminants, usually D65, that are slightly cooler or bluer than direct sunlight, which by contrast appears a pale amber or orange. (The effect is enhanced if a shaft of sunlight is observed within a darkened room.) Second, illuminating green, orange or red surface colors with more intense light appears to shift the color toward yellow, and to shift yellow surface colors toward white, as a result of changes in the proportional response of the S cones relative to the L and M cones at different luminance levels, and these shifts cause the illuminant to appear warm. Finally, the "white" appearance occurs for the same reason that very luminous hot metals, such as the filam