COLOR PERCEPTION
All
objects that we observe are focused sharply by the lens system of the eye on
its retina. The retina which is located at the back side of the eye has light
sensitive organs which measure the visual sensations.
The retina is connected with the optic nerve
which conducts the light stimulias sensed by the organs to the optical centre
of the brain. According to the theory formulated by Helmholtz the light
sensitive organs are of two types rods and cones.
The rods
provide brightness sensation and thus perceive objects only in various shades
of grey from black to white. The cones that are sensitive to color are broadly
in three different groups. One set of cones detects the presence of blue color
in the object focused on the retina, the second set perceives red color and the
third is sensitive to the green range. Each set of cones, may be thought of as
being ‘tuned’ to only a small band of frequencies and so absorb energy from a
definite range of electromagnetic radiation to convey the sensation of
corresponding color or range of color.
The
combined relative luminosity curve showing relative sensation of brightness
produced by individual spectral colors radiated at a constant energy level is
shown in Fig. It will be seen from the plot that the sensitivity of the human
eye is greatest for green light, decreasing towards both the red and blue ends
of the spectrum.
In fact the maximum is located at about 550
nm, a yellow green, where the spectral energy maximum of sunlight is also
located.
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