Now open your eyes again. If it is daytime, you will see that light is all around you.
What is Natural light?
The light sources that are not created by people are called natural light sources. They include the sun and the stars.
During the day, the rays of the sun light up the earth.
Sometimes, if there are no clouds, you can see the stars twinkling in the sky at night.
There are other sources of natural light, too. In some parts of the world, you can find insects called fireflies. They give off a pale, greenish-yellow light that flashes or glows in the dark.
Even deep down in the sea, some of the fish are able to produce flashes of light in the darkness. And if you live in the extreme northern or southern regions of the world, you might be able to see the aurora, a dazzling display of colored lights that flicker in the sky at night.
What is Artificial light?
These are called artificial sources of light.
Electric lights, oil lamps, and even candles are all artificial light sources. You can find your way in the dark by using a flashlight powered by batteries.
Television and movies are made by using light.
And city streets are often full of artificial lights—vehicle headlights, brightly colored advertisements, street lights, and neon lights.
Light does more than just enable us to see. We use beams of light to cut metals into complicated shapes, or to perform delicate surgical operations! Light even helps us to remain healthy.
When sunlight shines on our skin, our body makes a vitamin called vitamin D, which helps our teeth and bones to grow healthy.
Light and heat
Take a look around the room you’re sitting in. How many different things can you see that are able to give off, or emit, light? You could do a survey of the light sources in your home. Make a list of the light sources in each room of the house. Against each item on the list, write the color of the light and whether it gives off heat as well.
You ‘II probably find a lot of different objects that emit light at home. Do most of these give off heat?
Another kind of light called a fluorescent light is used to change more of the electrical energy into light and less into heat. Try holding your hand close to a fluorescent light. Does it feel as hot as the ordinary light bulb?
How does light travel?
The thin beam of strong light travels in a straight line until it hits this hand. This light is reflected off the hand and then travels in a different direction. Crossing the road would be easy!
Can light travel around corners?
This and other diagrams in this book show light rays as straight lines. The arrows indicate the direction in which the light travels.