During the day time, we can see things clearly. But we switch on the lights to see them at night. If we close our eyes we cannot see anything even during day time or at night with lights on. Why is that? So, let us find what requirements should be fulfilled to have “vision”.

 

How can we see?

Even though you close your eyes, the hand still gets light. Then, why didn’t you see the lines on the palm which you observed when your eyes were opened? To have a good vision, not only light but also the eye is important.

Therefore the main factors which are needed to see are;

1. 1. Source of light
   2. Eye

Sources of light

The main natural source of light is the sun. At night, we use bulbs, lamps, candles and other artificial sources to get light because there is no sunlight. Other than that, we get light even from the moon and stars at night.

We get light from these objects because they emit light. Such objects which emit light are known as sources of light.

Luminous and Non Luminous Objects

We can’t see anything when we enter a dark room. But if we light a bulb or a candle we will be able to see the candle and the bulb as well as other objects in the room. The reason is that the light emitted by the candle or the bulb enters our eye.

The objects which can produce their own light is called luminous objects.

Also there are some organisms which can produce there own light. Some types of mushrooms, glow worm, fire fly are some examples.

Objects which do not emit light are known as non luminous objects. To get a vision of such an object, a light ray of a luminous object must fall on it. Some non luminous objects are moon, planets, bed, chair etc.

Transmission of Light through Objects

When we look through some liquids, we can see both the objects and the light clearly. The reason is that light is transmitted well through such liquids. They are called Transparent objects. Glass and transparent colourless polythene are examples for transparent objects.

When we look through oil papers, unclear water, coloured cellophane papers, although the light can be seen, the objects cannot be clearly seen. Such objects are known as Translucent objects.

When we look through most of the objects we cannot see either the light or the object. For example, cardboard, wood, metal, paper, tar and etc. They are known as Opaque objects.

Light Rays and Light Beams

The narrow path in which light is transmitted known as a light ray. To show a light ray, we use a straight line with an arrow.

A light beam is made up of a collection of light rays. You have seen the light beam which is emitted from a torch when it is switched on.

We use several straight lines with arrow heads to show a light beam.

Applications of light

Light is a major need for proper vision. With the development of technology, we have changed the behavior of light and obtained many uses. Let us categorize the applications of light as follows.

For the production of food in plants

Unlike other living organisms, green plants can produce their own food. The energy needed for the process of food production is obtained from the sunlight. You all know that all other animals directly or indirectly depend on plants for food. Because of this, we consider that production of food in plants is the main advantage of light.

Light to give a clear vision

Earlier, people received light from natural objects such as the sun, the moon and stars. But after the invention of fire, man was able to produce light from various sources. With the development of technology, the light bulb was invented to get light. As a result there are many types of bulbs in the market.

Illumination

At present, most of the countries in the world use different coloured and patterned bulbs to illuminate various occasions. Large light sources are used in market places, populated streets and shopping complexes for advertisements.

As signals

Light houses release a powerful beam of light which gives the signal to the sailors that the land is close. In traffic lights, you may have seen the colours red, green and yellow. They individually give a message to the drivers and pedestrians. More attention is gained through the use of light to give such signals. Red is a colour which shows a danger.

For communication

Communication in the modern world is well developed. For this, different types of light rays are used. Telephone messages are transmitted through optic fibers. They are used to connect computer networks and high standard audio visual equipment.

In the medical field

At present, doctors use laser rays to treat eye patients, in heart operations and to treat wounds in the digestive system. This has increased the efficiency of treatments. With the use of optic fibers, the interior parts of the body are easily observed.

For entertainment

In musical shows and fairs, light is used in a large scale. They use spot lights of different colours to light up the stage. Even lights are used, in toys designed for children.

To produce light artificially we have to spend money. Therefore, unnecessary usage of light is a wastage of energy and money. So, we must always be cautious enough to stop the wastage of light and at the same time we must use it without making a disturbance to others