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What is Light?


What is light? Light is an electromagnetic wave made up of little packets of energy called photons.

 

Light is indispensable in our life. Without light we cannot imagine life on Earth. Our day-to-day activities would be inefficient and life would probably be boring in a world without light. So, we cannot take light lightly. Here, in this lesson we’re going to talk all about light.

 

How we see things?

What time of the day do you see things clearly? Day time or night time? Yes, it is the day time that you can get a clear vision of everything you see, because at night it is dark everywhere unless you turn the lights on or use a torch.

 

During the day time you see things very well thanks to the sunlight. The sun is the main source of light on earth.

What is Electromagnetic SpectrumWhat is Electromagnetic Spectrum? Read the lesson to know about it.

 

Without light from the sun, the world would be in darkness. At night we have to use an artificial source of light such as light bulbs, torches, electric lamps, candlelight etc. to get a clear vision of the things we see.

 

This indicates that we need to use some kind of a source of light to see. Without light we are unable to see, even though with eyes wide open.

 

You are reading this article now. You have enough of light to read it.

 

Now close your eyes.

 

Are you still reading this article? Or don’t have a clue what’s in the next line.

 

You wouldn’t be able to read this question, if you’ve actually closed your eyes. So, now probably you’ve opened your eyes back. Why? This is because you couldn’t see anything that you’re reading.

 

So, what does this indicate? Is only light enough to see things? No. We also need our eyes to see things. Here, eyes means, proper eyesight. People who are blind also have a pair of eyes, but they cannot see, because they don’t have their eyesight. People who are with poor eyesight need to wear a pair of spectacles or contact lenses to see things better.

 

Therefore, we need both light and proper eyesight to see things clearly.

 

What are the factors essential to see things better?

  • Light
  • Proper eyesight

 

What is light?

Light is an electromagnetic wave. It is the smallest quantity of energy that can be transported.

 

What is light made of?

Light is made up of little packets of energy. We call these Photons.

 

What is a photon?

A photon is an elementary particle which represents a quantum of light or other electromagnetic radiation.

 

A photon doesn’t have a real size.

 

A photon cannot be split. It can only be created or destroyed.

 

How is light produced?

We know light is radiated by a source of light, such as the Sun, light bulb, candle, torch etc. We also call these luminous sources.

 

(Click to read the lesson sources of light)

 

So, how do luminous sources radiate light?

 

When the atoms of a luminous source get heated up, it ‘excites’ the electrons of the atoms and gain extra energy. This extra energy is released as a photon. If the source of light gets hotter and hotter, it releases more photons. This is how luminous sources radiate light.

 

Example:

 

How does a light bulb emit light?

The energy comes from electricity to the light bulb. It heats the light bulb. This heat ‘excites’ the electrons of the atoms by gaining extra energy, which is released as photons, and the light bulb gives off light.

 

Energy conversion in a light bulbEnergy conversion in a light bulb

 

Next, let’s see how can light be an electromagnetic wave.

 

Electromagnetic Spectrum

 

What is electromagnetic spectrum?

Electromagnetic spectrum is the enormous range of wave lengths and frequencies over which electromagnetic radiation extends.

 

Visible light is only a tiny part of electromagnetic spectrum.

 

So, visible light is a type of energy in form of electromagnetic radiation.

 

Electromagnetic radiation consists of enormous range of wave lengths and frequencies, such as gamma rays, UV rays, visible light, radio waves etc.

 

Components of Electromagnetic SpectrumComponents of Electromagnetic Spectrum

 

Electromagnetic SpectrumElectromagnetic Spectrum

 

Light Rays and Light Beams

What is a ray of light?

A ray is the direction of the path in which light is travelling.

 

A ray is represented in diagrams by a straight line with an arrow on it.

 

A Light RayA Light Ray

 

What is a beam of light?

A beam is a stream of light.

 

It is shown by a number of rays and can be three types: parallel, diverging (spreading out) or converging (getting narrower).

 

A Light BeamA Light Beam

 

Different types of beams of lightDifferent types of beams of light

 

Have you seen sunbeams streaming through trees early in the morning or light from a cinema projector on its way to the screen? If the answer is yes, then you have seen how light travels in straight lines. These beams are visible, since the dust particles in the air reflect light into our eyes.

 

Sunbeams streaming through cloudsSunbeams streaming through clouds

 

Sunbeams streaming through cloudsSunbeams streaming through clouds

 

Sunbeams streaming through cloudsSunbeams streaming through clouds

 

Sunbeams streaming through treesSunbeams streaming through trees

 

Sunbeams streaming through treesSunbeams streaming through trees

 

Sunbeams streaming through treesSunbeams streaming through trees

 

Uses of light

 

  • For photosynthesis
  • Photosynthesis - Light is essential for plants to make food through the process, 'photosynthesisLight is essential for plants to make food through the process, ‘photosynthesis’.

     

  • For clear vision
  • Clear vision - Without light we cannot get a clear vision of anything that we seeWithout light we cannot get a clear vision of anything that we see.

     

  • For illumination
  • IlluminationIllumination is done during festive seasons, for advertising purposes etc. using colourful light bulbs.

     

  • For signs
  • Road signsColour lights give messages to drivers and pedestrians like when to stop, get ready and move. Road signs are non-incandescent objects which glow in the dark. (Click to read the lesson sources of light).

     

  • For light like laser in communication and medical fields

 

Laser light

Laser light sources work differently than the normal sources of light.

 

In laser light sources the excited atoms act together and emit a narrow, very bright beam of light.

 

The first laser was invented in 1960.

 

Laser LightLaser Light

 

Host of applications of laser

Laser is used vastly in the field of medicine, industry, and agriculture. Read the following list of uses of laser in today’s world.

 

Laser is used in;

  • industry to cut through plate metal
  • scanners to read bar codes at shop and library checkouts
  • CD players
  • optical fibre telecommunication systems to send telephone messages and to maintain internet connections
  • welding in electronic circuits
  • printing
  • holography to generate 3D images of objects
  • surveying
  • range-finding
  • developing hidden finger prints
  • delicate medical operations on the eye (Laser beams are used as a surgical tool for welding detached retinas) or inner ear
  • surgery to break the stones in human kidneys and destroy tumors, cancerous and pre-cancerous cells
  • heart surgery and to treat wounds in the digestive system