1. LIGHT AND THE HUMAN EYE
Liezel Oosthuizen
200932201

2. WHAT IS LIGHT?
 Light is a form of energy, that can be detected by our sense of sight.
Scientists also call light electromagnetic radiation (EM) and travels in
straight lines. Light is visible which humans can see and this light is
known as visible light.
 Did you know?
 Dogs can see only shades of grey.
 Some insects can see light from the ultraviolet part of the spectrum.
 How fast does light travel?
 About 300,000 kilometres per second.

3. THERE ARE 3 WAYS THAT LIGHT FALLS ONTO AN
OBJECT:
 1. Block it with something which is also known as the - FORMATION OF A SHADOW.
 The formation of a shadow is: When an object forms a shadow against a wall when a light shines on
it.
 2. Reflecting it by changing its path with a mirror - This is called a REFLECTION.
 Reflection is: When a light ray hits an object and bounces off. When you think of reflection, think
about mirrors. They reflect all of the light. That is the reason you can see yourself in a mirror.
 3. Bend it - Change its direction by making it pass into another transparent material of
different density, like glass or water. This is called REFRACTION, and it's how lenses work.
 Refraction is: The bending of light as it passes from one transparent substance to another, like air to
water, it then changes speed and direction. That change in direction is called refraction. Light is
refracted only when it hits a surface at an angle. A light ray slows down when it bends towards the
normal. The normal is a line drawn perpendicularly to the reflecting surface of the point of
incidence.
 Light is produced, controlled, and detected in so many ways around you!

4. concave
LENSES
convex
 What are lenses?
A lens bends light in a certain way. Most devices that
control light have one or more lenses inside of them.
 There are TWO basic lens types:
 CONVEX - CONVEX or POSITIVE lenses will
CONVERGE or FOCUS light and can form an IMAGE.
 CONCAVE - CONCAVE or NEGATIVE lenses will
spread out light rays.

5. THE SPECTRUM OF COLOURS
• Can you split light???
YES! White light consist of a number of colours and these colours disperse its
colours with a triangular prism .
• Primary Colours
The following information can be given regarding the colour of objects:
• Green plants are green because they absorb all other colours of the spectrum except the colour
green.
• A red flower reflects the colour red and absorbs all other colours.
• A black object absorbs all the light that falls on it.
• A white light reflects the light that falls on it.
• E.g. When you wash washing. Will the dark/black washing dry first or will the white coloured
washing dry first?
• *The black washing will dry first, because the colour black absorbs light quicker.

6. THE HUMAN EYE
• Look at all the objects around you. How is it possible that you can see
everything?
• Its is actually light rays that are reflected by the objects.
• The sight of your eye processes tons of information and allows us to see
different colors, movements, shapes and dimensions of different
objects in the world by processing light that the eye emits or reflects.
The eye is able to detect a sharp- or dim light.
• With the absence of light the human eye will not be able to sense an
object.
• The human eye is the size of a ping-pong ball and sits inside the skull in
a hollow eye socket.
• The eyelid protects the front part of the eye. The lid helps keep the
eye clean and moist by blinking several times a minute.
• The front white part of the eyeball is known as the sclera.

7. HOW DOES LIGHT TRAVEL THROUGH THE HUMAN EYE?
 The light ray from an object enters the eye first
through tick clear tissue called the cornea, which is
right in front and this part also protects the eye. It’s
like a window that allows light to enter the eye.
 The outer part of the eyeball which protects the eye
is white of colour and it is called the sclera.
 After that the light moves then through the pupil,
which is the black circle in the middle of your eye.
It also helps light to travel through the lens.
 When the light rays move through the pupil, the iris
helps the pupil to change shape, depending on the
amount of light entering the eye opening.
 The iris has two sets of muscles: A bright light
makes the muscle contract and the pupil becomes
smaller, which lets less light through and the other
muscle helps the pupil become bigger when a dim
light shines through the eye and this means more
light can move through towards the lens.
 The lens focuses light rays on the back of the
eyeball called the retina.
A bright light.
 When light passes through the lens the image falls on
the retina and actually appears upside down. Your
brain does the work and turns it the right side up so
that you can identify what you see.
 The optic nerve sends important messages from the
eye to the brain so that you can identify an object
correctly.
A dim light.

8. HOW THE LENS CHANGES IT’S SHAPE WHEN LIGHT
COMES FROM DIFFERENT DISTANCES
 A Far Object:  Close object:
 The ciliary muscles  The ciliary muscles
relax away from the contract towards the
lens. This pulls on the lens. This makes the
ligaments and they ligaments slack and
pull on the the elastic lens goes
lens, making it less back to its rounded
rounded. shape.
Rays from a nearby
Rays from a distant are object are focused on the
focused on the retina by a retina by a more rounded
flattened lens. lens.

9. HOW LIGHT TRIGGERS AN IMPULSE TO THE BRAIN
1. Light hits a
receptor cell in the
retina.
2. A light-sensitive
4. The light-sensitive chemical in the cell
chemical is remade. breaks down.
3. The breakdown of
the chemical triggers
an impulse to pass to a
nerve cell connected
to the brain.

10. INTERESTING FACTS
 Most people blink their eyes every 2-10 seconds.
 Every time you blink your eyes, they will be closed
for 0,3 seconds. That means that your eyes will
be at least closed everyday for 30 minutes just by
blinking your eyes.
 If you only have one eye, you will see everything
two dimensional.
 Every 1 in 10 men are colour blind. Colour blind
people can only see certain colours. In certain
cases they can only see black, grey and white.

11. PICTURES OF THE HUMAN EYE AND ILLNESSES:

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