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Subject knowledge: What is light?

The scientific definition of light is a form of energy that travels from one place to another. The Oxford Dictionary defines light as ‘the energy from the sun, a lamp, etc. that makes it possible to see things’.

Light is a form of energy and visible light is a form of radiation. Other forms of light are not visible by the human eye and these include infrared, ultraviolet, x-rays and microwaves. The visible spectrum is shown as:

A diagram representing the electromagnetic spectrum, with different wavelengths grouped from gamma rays (left) to long radio waves (right). Visible light is approximately in the middle between 400-700 nanometres wavelength blue to red Source: Wikimedia Commons. Used under CC-SA license.

White light is the light we usually see from the sun, but it is actually made up from many different colours. These different colours can be seen when sunlight is refracted, or ‘split’, as it passes through water droplets in the air and creates a rainbow.

Light appears to travel in a straight line from its source and travels incredibly fast, 299,792 kilometers per second. This means that it can travel the same distance as the circumference of the Earth 8 times in one second! It takes just over 8 minutes for light from the sun to reach Earth and 5.5 hours for it to reach Pluto. This gives an idea of how vast our solar system is! Light also does not need a medium (gas, liquid or solid) to travel through, therefore it is able to travel through a vacuum and therefore space.

How we see

Light allows us to see things. Without light the world would be completely dark and we would be unable to see anything. This is a difficult concept for children to understand because usually they will have had little experience of complete darkness. Even at night there is ambient light and it is difficult to create a completely dark space.

In order to see we need light to bounce off, or reflect off, objects and into our eyes. We often understand this when talking about mirrors and other shiny objects, as we talk about being able to see our reflection. However light is reflected off all things that we see, some are just better at reflecting than others.

All objects absorb some of the light energy as it hits them and the degree to which they do this means they can be categorised as:

  • Transparent: lets all light through
  • Translucent: absorbs some light, lets other light through
  • Opaque: absorbs all light, allows none through and creates a shadow behind the material.

Describe

If you had to describe what light is in one sentence how would you do this?

What vocabulary is important to use?

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This article is from the free online course:

Teaching Primary Science: Physics

National STEM Learning Centre