This document discusses color and color perception. It explains that color is the visual property corresponding to categories like red, blue, etc., derived from the spectrum of light interacting with the eye. The document then provides the wavelength ranges for colors in the visible light spectrum. It describes how objects reflect or absorb different wavelengths, which determine the color perceived. Cones in the retina detect light wavelengths and send signals to the brain to perceive color. The document notes common uses of color in signs, with red indicating danger and green indicating safety instructions. It emphasizes the importance of adequate color contrast in human factors engineering for visibility, identification, aesthetics, and avoiding stress or fatigue.

2. Color:-
 It is the visual perceptual property
corresponding in humans to the
categories called red, blue, yellow,
green and others. Color derives from
the spectrum of light(distribution of
light power versus wavelength)
interacting in the eye with the spectral
sensitivities of the light receptors.
Color categories and physical
specifications of color are also
associated with objects or materials
based on their physical properties
such as light absorption, reflection, or
emission spectra.

3. Electromagnetic radiation is characterized by its wavelength (or frequency) and its intensity. When
the wavelength is within the visible spectrum (the range of wavelengths humans can perceive,
approximately from 390 nm to 700 nm), it is known as "visible light".
The colors of the visible light spectrum[1]
color
wavelength
interval
frequency
interval
red
~ 700–
635 nm
~ 430–
480 THz
orange
~ 635–
590 nm
~ 480–
510 THz
yellow
~ 590–
560 nm
~ 510–
540 THz
green
~ 560–
490 nm
~ 540–
610 THz
blue
~ 490–
450 nm
~ 610–
670 THz
violet
~ 450–
400 nm
~ 670–
750 THz

4. HOW DO OUR
EYES SEE
color

5. When light hits an
object – say, a banana
– the object absorbs
some of the light and
reflects the rest of it.
Which wavelengths
are reflected or
absorbed depends on
the properties of the
object.
For a ripe banana,
wavelengths of about
570 to 580
nanometers bounce
back. These are the
wavelengths of yellow
light.

6. TELL ME WHAT YOU SEE the
color of object?
THE COLOR WHICH THE
OBJECT REFLECTS OR
ABSORBS ?

7. When you look at a banana,
the wavelengths of reflected light
determine what color you see.

8. The light waves
reflect off the
banana's peel and
hit the light-sensitive
retina at
the back of your
eye. That's where
cones come in.

9. Cones are one type of
photoreceptor, the tiny
cells in the retina that
respond to light. Most
of us have 6 to 7 million
cones, and almost all of
them are concentrated
on a 0.3 millimeter spot
on the retina called the
fovea centralis.
When light from the
banana hits the cones, it
stimulates them to
varying degrees. The
resulting signal is
zapped along the optic
nerve to the visual
cortex of the brain,
which processes the
information and returns
with a color: yellow.

10. COLORS USED AS SIGNS :-
 Danger signs: RED.
 Caution signs: YELLOW.
 Safety instruction signs: GREEN.
 Directional signs: BLACK.
 Informational signs: A variety of colors may be used,
except for red, yellow, or magenta (purple).

11. DANGER SIGNS :-
Danger signs should only
be used when immediate
hazard exists. There will
be no variations in the
type or design of signs
posted to warn of
specific danger. All
personnel will be
instructed that danger
signs indicate immediate
danger and that special
precautions are necessary

12. CAUTION SIGNS :-
Caution signs should be
used only to warn against
potential hazards or to
caution against unsafe
practices. All personnel
will be instructed that a
caution sign indicates a
possible hazard against
which proper precautions
will be taken

13. DIRECTIONAL SIGNS :-
Directional signs should
be used in sufficient
numbers to indicate the
way to stairways, fire
escapes, exits, and other
locations. Many other
safety media are
available for use in
military maintenance
shops.

14. Safety instruction signs:
GREEN.

15. Contrast:-
 Contrast is the difference in luminance and/or color that makes an object (or its
representation in an image or display) distinguishable. In visual perception of the
real world, contrast is determined by the difference in the color and brightness of the
object and other objects within the same field of view. Because the human visual
system is more sensitive to contrast than absolute luminance, we can perceive the
world similarly regardless of the huge changes in illumination over the day or from
place to place. The maximum contrast of an image is the contrast ratio or dynamic
range.

16. Changes in the
amount of contrast
in a photo

17. Images of different contrasts:-

18. Examples:-

20. Color in Interior Design:-
Changing a room’s color
can affect the mood

21. Importance of color contrast in HFE:-
 If its contrast is poor it leads to poor visibility.
 If machines are not numbered with correct colors there will be lagging in time, as it
takes lot of time to identify the machine.
 Manufacturers should see that the colors are aesthetically good.
 When the products are coded with colors they should see that the colors are not to
bright or too low to see them.
 When a worker who continuously works on a machine ,which is not correctly coded
with colors then he would be stressed or feel fatigue or irritated which directly
shows affect on production.

22. Taking color contrast into account is must in Human
Factors Engineering.