Color
Color is not a physical property of the things we see—it is the consequence of
light waves bouncing off or passing through various objects.
The color of an object or surface is deter-
mined by its reflected or transmitted light.
Color is not a physical property of the things
we see—it is the consequence of light waves
bouncing off or passing through various
objects. What is perceived as color is the
result of materials reflecting or transmitting
energy in particular regions of the visible
spectrum.
Green glass transmits the green portion
of the spectrum, absorbing almost all of the
other regions; yellow paint reflects the yellow
portion, absorbing almost all other wave-
lengths (figure 4.1). White or neutral gray
materials reflect all wavelengths in approxi-
mately equal amounts.
Pure spectral colors are specified by
their wavelength, which is usually expressed
in nanometers. A nanometer (nm) is one bil-
lionth of a meter or about thirty-nine bil-
lionths of an inch.
The reflectance chart (color plate 9)
shows that butter absorbs blue light and
reflects a high percentage of all other colors;
these other colors combine to produce what
we call yellow. Green lettuce reflects light
with wavelengths primarily in the 500–600-
nm region and absorbs all of the energy at
other wavelengths. A tomato is red only
because it reflects visible energy at 610 nm
while absorbing almost all of the other wave-
lengths.
A light source that emits radiant energy
comparatively balanced in all visible wave-
lengths appears “white” in color. Passing a
narrow beam of this white light through a
prism separates and spreads the individual
wavelengths, allowing the eye to distinguish
among them. The resulting visual phenome-
non is called acolor spectrum(color plate
2).
“White” light sources emit energy at all
or almost all visible wavelengths, but not
always in an ideal proportion. Almost all
sources are deficient at some wavelengths
yet still appear to be white. This deficiency
influences the perception of colors; the
effect is known ascolor rendition. It causes
the graying of some colors while enhancing
the vividness of others.
To provide accurate color perception, a
light source must emit those wavelengths
that a material reflects. Lighting a tomato’s
surface with a white light source makes the