LIGHT AND THE HUMAN EYE

Liezel Oosthuizen

200932201

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.

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!

LENSES

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.

convex

concave

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.

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.

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 irishelps 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.

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.

A bright light.

HOW THE LENS CHANGES IT’S SHAPE WHEN LIGHT

COMES FROM DIFFERENT DISTANCES

A Far Object:

The ciliary muscles

relax away from the

lens. This pulls on the

ligaments and they

pull on the

lens, making it less

rounded.

Close object:

The ciliary muscles

contract towards the

lens. This makes the

ligaments slack and

the elastic lens goes

back to its rounded

shape.

Rays from a distant are

focused on the retina by a

flattened lens.

Rays from a nearby

object are focused on the

retina by a more rounded

lens.

HOW LIGHT TRIGGERS AN IMPULSE TO THE BRAIN

1. Light hits a receptor cell in the

retina.

2. A light-sensitive chemical in the cell

breaks down.

3. The breakdown of the chemical triggers

an impulse to pass to a nerve cell connected

to the brain.

4. The light-sensitive chemical is remade.

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.

PICTURES OF THE HUMAN EYE AND ILLNESSES:

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