Physics of Light
Light:
Electromagnetic energy whose wavelength is
between 400 nm and 700 nm
COLOR
Visual description of an observer by which he distinguishes two fields of same size,
shape and structure by difference in spectral activity.
- Purely sensory phenomenon and not a physical attribute
- Perception of colour depends upon spectral composition of light:
- coming from an object &
- emanating from surrounding
- State of light adaptation of subject
Primary Colors : Red, Green,Blue
Secondary Colors : Cyan, Magenta,Yellow
Color sense
Ability of the eye to discriminate between different colors excited by
light of different wavelengths
Function of cones
Better appreciated in photopic vision
In scotopic vision all colors seen as gray-called Purkinje shift
Young Helmholtz Maxwell Theory
Trichromatic theory
Postulates three different receptors maximally sensitive to
wavelength in different regions of visual spectrum.
Three peaks are
440 to 450 nm – blue spectrum
535 to 550 nm – green spectrum
570 to 590 nm – red spectrum
Color sensation
Determined by relative frequency of impulses from each cone
system
A given color consists of admixture of 3 primary colors in different
proportion
Yellow color perception is due to simultaneous stimulation of red
and green
Color Interpretation
White Color
Stimulation of all red, green & blue cones
gives white color
No single wavelength of light matching to
white color
For getting white color all the cones must
be stimulated at the same equally
Color Blindness
Three types
- Trichromats
- Dichromats
- Monochromats
Color Blindness
When a single group of color receptive cones is missing from the
eye, the person is unable to distinguish some colors from others
Between 525 and 675nm wavelength green, yellow, orange, and
red colors are perceived
Appreciated by the red and green cones
Any of the two cones is missing, the person is unable to distinguish
these colors
Known as red green color blindness
Loss of red cones is called a protanope
Visual spectrum is shortened at longer wavelength end due to
absence of red cones
Color-blind person who lacks green cones is called a deuteranope
Normal visual spectrum because red cones are able to detect the
long wavelength red color
Red-green Color Blindness
Is a genetic disorder occurs exclusively in males
Genes in female X chromosome code for the
respective cones
Females are carrier for color blindness
Color blindness almost never occurs in females
Reason:
X chromosome carry the genes so one of the X
chromosome might have gene of color vision
Color Vision Charts
Ishihara Chart
Friends Chart
Edridge-green lantern
Holmgrens wool matching method
