Let’s talk about the sources of light in this lesson.
Any source or object which emits its own light is a source of light.
Anything that gives off light of its own is said to be luminous. Every source of light is a luminous object.
Do you know what the Earth’s main source of light is? Yes it is the Sun. The sun is the main source of light on earth.
Without light from the sun, the world would be in darkness. Plants wouldn’t grow and no other life would exist on Earth. The sun gives us energy to survive. Light makes up only a small fraction of the energy that comes to us from the sun.
Light sources can be two groups.
Following is a list of light sources;
Natural light sources produce light naturally without any human involvement.
Artificial light is light made by humans.
Emitting light as a result of being heated is called incandescent. This means, when an object is incandescent, it emits light because it is hot. Most of the light sources are incandescent.
Examples of incandescent light sources
Some sources of light emit light without getting hot. These can be both living and non living things. Fluorescent tubes, glow-in-the-dark paints, glow-in-the-dark signs, glow-in-the-dark stickers and sticks, glow-worms, fireflies, jellyfish are some of the examples for light sources that emit light without getting hot.
Living things that emit light without getting hot are referred to as bioluminescent.
Examples of bioluminescent light sources
The ocean is in complete darkness from a depth of about 1000 metres downwards. This is because, light from the surface does not reach deep below the ocean. This causes problems for the fish to find food. Some deep-sea fish swim closer to the surface to get food whereas some fish spend all of their time in the dark. Angler fish, viperfish and black dragonfish are some of the examples of fish who spend their entire life in the dark.
Objects which do not emit light or reflect the light from luminous objects are called non-luminous objects.
Some non-luminous objects reflect light struck on them from luminous objects. One good example is the moon. The moon just reflects light from the sun.
Reflectors of light cannot emit their own light. They just reflect light.
Examples of reflectors of light
Look at the beautiful reflections of the surrounding environment in the smooth water of this stream.
Why are mirrors not sources of light?
Mirrors do not make their own light. They just reflect light. That is why you cannot see a mirror in a completely dark room.
Is the moon source of light?
No, it isn’t. The moon is not a source of light because it just reflects light from the Sun.
Remember! You must not look directly at the Sun because, Sun is a very bright object which can damage your eyes very quickly.
Did you know there is invisible light that your eyes cannot see?
Infrared (IR) and Ultraviolet (UV) are the two types of invisible light.
Living things and very hot objects like the Sun give out infrared.
Ultraviolet is very powerful light that is given out by the Sun. UV light can damage your eyes. This is why you shouldn’t directly look at the Sun. Ultraviolet also causes severe sunburn and skin cancer. You should always remember to use sunscreen before exposing to the direct sunlight.