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The human eye and the colourful world
The human eye is an 
organ that reacts to light 
and has several purposes. 
As a sense organ, the 
mammalianeye allows visi 
on. Rodand cone cells in 
the retina allow conscious 
light perception and 
vision including color differentiation and the 
perception of depth. The human eye can 
distinguish about 10 million colors.
WORKING OF HUMAN EYE 
The individual components of the eye work in a manner 
similar to a camera. Each part plays a vital role in providing 
clear vision. So think of the eye as a camera with the cornea, 
behaving much like a lens cover. As the eye 's main focusing 
element, the cornea takes widely diverging rays of light and 
bends them through the pupil, the dark, round opening in 
the center of the colored iris. The iris and pupil act like the 
aperture of a camera. 
Next in line is the lens which acts like the lens in a camera, 
helping to focus light to the back of the eye. Note that the 
lens is the part which becomes cloudy and is removed during 
cataract surgery to be replaced by an artificial implant 
nowadays. 
The Camera The Human Eye
The human eye and the colourful world
The iris control the amount of light entering the 
eyes. The iris automatically adjust the size of the 
pupil according to the intensity of light received by 
the eye. If the amount of light received by the eye 
is large (as during the day time ),then the iris 
contracts the pupil (makes the pupil small) and 
reduces the amount of light entering the eye. On 
the other hand , if the amount of light received by 
the eye is small(as the room is dark)the iris 
expands the pupil (make the pupil large ) so that 
more light may enter the eyes. 
 The adjustment of the size of pupil takes some 
time .
The human eye and the colourful world
The human eye and the colourful world
The retina of our eye has a large number of light – 
sensitive cells. There are two kinds of light-sensitive 
cells on the retina: rods and cones .
Rod cells, or rods, 
are photoreceptor cells in 
the retina of the eye that can 
function in less 
intense light than the other 
type of visual 
photoreceptor, cone cells. 
Cone cells, or cones, are one 
of the two types 
of photoreceptor cells that 
are in the retina of 
the eye which are 
responsible for color 
vision as well as eye color 
sensitivity; they function best 
in relatively bright light, as 
opposed to rod cells that 
work better in dim light.
Accommodation (eye) 
Accommodation (Acc) is the process by which the 
vertebrate eye changes optical power to maintain a 
clear image or focus on an object as its distance 
varies. 
Accommodation acts like a reflex, but can also be 
consciously controlled. Mammals, birds and reptiles 
vary the optical power by changing the form of the 
elastic lens using the ciliary body (in humans up to 
15 dioptres). Fish and amphibians vary the power by 
changing the distance between a rigid lens and the 
retina with muscles.[1]
The human eye and the colourful world
The human eye and the colourful world
Myopia 
Myopia commonly known as near-sightedness 
(American English) and short-sightedness (British 
English), is a condition of the eye where the light 
that comes in does not directly focus on the retina 
but in front of it, causing the image that one sees 
when looking at a distant object to be out of 
focus, but in focus when looking at a close object.
This figure shows an defect 
called myopia. In this case, the 
parallel rays of light coming 
from the distant object are 
converged to form an image in 
front of the retina due to 
which the eye cannot see the 
distant object clearly. Myopia 
is corrected by using 
spectacles containing 
concave lenses. When concave 
lens is placed in front of the 
myopic eye as shown in figure 
then the parallel rays of light 
coming from the distant 
object at the far point of 
myopic eye. Since the rays of 
light now appear to be 
coming from the eye’s far
Hypermetropia (Hyperopia) - Long Sighted 
The defects of eye 
called hypermetropia is 
caused : 
i. Due to low 
converging power of 
eye-lens, 
ii. Due to eye –ball 
being too small.
Hypermetropia means long sight and 
is where the image of nearby object 
is formed behind the retina. This 
could be because the eye is too 
short, or the cornea or crystalline lens 
does not refract the light enough. 
A hypermetropic person may have 
blurred vision when looking g at 
objects close to them, and clearer 
vision when looking at objects in the 
distance. By placing a convex (plus 
powered) lens in front of a 
hypermetric eye, the image is moved 
forward and focuses correctly on the 
retina.
Presbyopia 
Presbyopia is a condition associated with 
aging in which the eye exhibits a 
progressively diminished ability to focus on 
near objects. Presbyopia’s exact 
mechanisms are not fully understood; 
research evidence most strongly supports a 
loss of elasticity of the crystalline lens, 
although changes in the lens’ curvature 
from continual growth and loss of power of 
the ciliary muscles (the muscles that bend 
and straighten the lens) have also been 
postulated as its cause.
This defect is corrected in the same way as 
hypermetropa is by using spectacles having 
convex lenses.
Cataract 
A cataract is a clouding of the lens inside 
the eye which leads to a decrease in vision. It is 
the most common cause of blindness and is 
conventionally treated with surgery. Visual loss 
occurs because opacification of 
the lens obstructs light from passing and being 
focused on the retina at the back of the eye. 
It is most commonly due to aging, but has many 
other causes.
Over time, yellow-brown pigment is deposited in 
the lens, and this, together with disruption of the 
lens fibers, reduces the transmission of light and 
leads to visual problems. 
Those with cataracts often experience difficulty in 
appreciating colors and changes in contrast, 
driving, reading, recognizing faces, and coping 
with glare from bright lights.
The human eye and the colourful world
The human eye and the colourful world
Scattering of light 
Scattering of light Means to 
throw light in various random 
directions
Scattering of sun light passing through the canopy of a 
forest
Scattering of light
The human eye and the colourful world
The human eye and the colourful world
The human eye and the colourful world
The human eye and the colourful world
The human eye and the colourful world
A rainbow is an optical and 
meteorological 
phenomenon that is 
caused by both reflection 
and refraction of light in 
water droplets resulting in 
a spectrum of light 
appearing in the sky. It 
takes the form of a 
multicolored arc . 
Rainbows caused by 
sunlight always appearin 
the section of sky directly 
opposite the sun.
The Steps Involved in the 
formation of a rainbow 
1. Light from sun strikes raindrop. 
2. Some of the light is reflected. 
3. The rest of the light is 
refracted. 
4. White light splits into 
component colors. 
5. Light is refracted again as it 
leaves raindrop. 
6. Colors are further dispersed.
POSITION OF STARS 
AND 
TWINKLING OF STARS
The human eye and the colourful world
The human eye and the colourful world

The human eye and the colourful world
Why is the Sky Blue? 
1. The blue color of the sky is due 
to Rayleigh scattering. As light 
moves through the atmosphere, 
most of the longer wavelengths 
pass straight through. Little of 
the red, orange and yellow light 
is affected by the air. 
2. However, much of the shorter 
wavelength light is absorbed by 
the gas molecules. The absorbed 
blue light is then radiated in 
different directions. It gets 
scattered all around the sky. 
Whichever direction you look, 
some of this scattered blue light 
reaches you. Since you see the 
blue light from everywhere 
overhead, the sky looks blue. 
3.As you look closer to the horizon, 
the sky appears much paler in color. 
To reach you, the scattered blue light 
must pass through more air. Some of it 
gets scattered away again in other 
directions. Less blue light reaches your 
eyes. The color of the sky near the 
horizon appears paler or white.
The human eye and the colourful world
The human eye and the colourful world
 Cloud particles are large enough 
to scatter any color of light that 
falls on them. The repeated 
scattering of light, called multiple 
scattering, causes whitish light 
because enough light of all colors 
is scattered to your eye, and those 
colors combine to make white 
light. 
•When light beams 
interact with particles 
suspended in air, 
some of the energy is 
scattered, which 
means the light beam 
changes direction, 
and usually color as 
well. The amount of 
light scattered is a 
function of the size 
of the particle 
relative to the 
wavelength of light 
falling on it.
The human eye and the colourful world
At sunrise or 
sunset, however, 
when the Sun is 
low on the 
horizon, the light 
rays must pass 
through more of 
the atmosphere – 
and therefore 
bounce off more 
molecules – than 
at other times of 
day. This means 
that more blue 
light gets 
scattered away 
before the light 
reaches your 
eyes. 
Other colours – such as red, orange 
and yellow – can therefore continue 
to pass through the atmosphere 
unaffected, creating beautiful 
colours at the start and end of the 
day.
The human eye and the colourful world

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The human eye and the colourful world

  • 2. The human eye is an organ that reacts to light and has several purposes. As a sense organ, the mammalianeye allows visi on. Rodand cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can distinguish about 10 million colors.
  • 3. WORKING OF HUMAN EYE The individual components of the eye work in a manner similar to a camera. Each part plays a vital role in providing clear vision. So think of the eye as a camera with the cornea, behaving much like a lens cover. As the eye 's main focusing element, the cornea takes widely diverging rays of light and bends them through the pupil, the dark, round opening in the center of the colored iris. The iris and pupil act like the aperture of a camera. Next in line is the lens which acts like the lens in a camera, helping to focus light to the back of the eye. Note that the lens is the part which becomes cloudy and is removed during cataract surgery to be replaced by an artificial implant nowadays. The Camera The Human Eye
  • 5. The iris control the amount of light entering the eyes. The iris automatically adjust the size of the pupil according to the intensity of light received by the eye. If the amount of light received by the eye is large (as during the day time ),then the iris contracts the pupil (makes the pupil small) and reduces the amount of light entering the eye. On the other hand , if the amount of light received by the eye is small(as the room is dark)the iris expands the pupil (make the pupil large ) so that more light may enter the eyes.  The adjustment of the size of pupil takes some time .
  • 8. The retina of our eye has a large number of light – sensitive cells. There are two kinds of light-sensitive cells on the retina: rods and cones .
  • 9. Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells. Cone cells, or cones, are one of the two types of photoreceptor cells that are in the retina of the eye which are responsible for color vision as well as eye color sensitivity; they function best in relatively bright light, as opposed to rod cells that work better in dim light.
  • 10. Accommodation (eye) Accommodation (Acc) is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. Accommodation acts like a reflex, but can also be consciously controlled. Mammals, birds and reptiles vary the optical power by changing the form of the elastic lens using the ciliary body (in humans up to 15 dioptres). Fish and amphibians vary the power by changing the distance between a rigid lens and the retina with muscles.[1]
  • 13. Myopia Myopia commonly known as near-sightedness (American English) and short-sightedness (British English), is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it, causing the image that one sees when looking at a distant object to be out of focus, but in focus when looking at a close object.
  • 14. This figure shows an defect called myopia. In this case, the parallel rays of light coming from the distant object are converged to form an image in front of the retina due to which the eye cannot see the distant object clearly. Myopia is corrected by using spectacles containing concave lenses. When concave lens is placed in front of the myopic eye as shown in figure then the parallel rays of light coming from the distant object at the far point of myopic eye. Since the rays of light now appear to be coming from the eye’s far
  • 15. Hypermetropia (Hyperopia) - Long Sighted The defects of eye called hypermetropia is caused : i. Due to low converging power of eye-lens, ii. Due to eye –ball being too small.
  • 16. Hypermetropia means long sight and is where the image of nearby object is formed behind the retina. This could be because the eye is too short, or the cornea or crystalline lens does not refract the light enough. A hypermetropic person may have blurred vision when looking g at objects close to them, and clearer vision when looking at objects in the distance. By placing a convex (plus powered) lens in front of a hypermetric eye, the image is moved forward and focuses correctly on the retina.
  • 17. Presbyopia Presbyopia is a condition associated with aging in which the eye exhibits a progressively diminished ability to focus on near objects. Presbyopia’s exact mechanisms are not fully understood; research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens’ curvature from continual growth and loss of power of the ciliary muscles (the muscles that bend and straighten the lens) have also been postulated as its cause.
  • 18. This defect is corrected in the same way as hypermetropa is by using spectacles having convex lenses.
  • 19. Cataract A cataract is a clouding of the lens inside the eye which leads to a decrease in vision. It is the most common cause of blindness and is conventionally treated with surgery. Visual loss occurs because opacification of the lens obstructs light from passing and being focused on the retina at the back of the eye. It is most commonly due to aging, but has many other causes.
  • 20. Over time, yellow-brown pigment is deposited in the lens, and this, together with disruption of the lens fibers, reduces the transmission of light and leads to visual problems. Those with cataracts often experience difficulty in appreciating colors and changes in contrast, driving, reading, recognizing faces, and coping with glare from bright lights.
  • 23. Scattering of light Scattering of light Means to throw light in various random directions
  • 24. Scattering of sun light passing through the canopy of a forest
  • 31. A rainbow is an optical and meteorological phenomenon that is caused by both reflection and refraction of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicolored arc . Rainbows caused by sunlight always appearin the section of sky directly opposite the sun.
  • 32. The Steps Involved in the formation of a rainbow 1. Light from sun strikes raindrop. 2. Some of the light is reflected. 3. The rest of the light is refracted. 4. White light splits into component colors. 5. Light is refracted again as it leaves raindrop. 6. Colors are further dispersed.
  • 33. POSITION OF STARS AND TWINKLING OF STARS
  • 36.
  • 38. Why is the Sky Blue? 1. The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air. 2. However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue. 3.As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.
  • 41.  Cloud particles are large enough to scatter any color of light that falls on them. The repeated scattering of light, called multiple scattering, causes whitish light because enough light of all colors is scattered to your eye, and those colors combine to make white light. •When light beams interact with particles suspended in air, some of the energy is scattered, which means the light beam changes direction, and usually color as well. The amount of light scattered is a function of the size of the particle relative to the wavelength of light falling on it.
  • 43. At sunrise or sunset, however, when the Sun is low on the horizon, the light rays must pass through more of the atmosphere – and therefore bounce off more molecules – than at other times of day. This means that more blue light gets scattered away before the light reaches your eyes. Other colours – such as red, orange and yellow – can therefore continue to pass through the atmosphere unaffected, creating beautiful colours at the start and end of the day.