Sight is one of our senses. Our receptor for light is the eye. It used to be though that something emerged from our eyes to sense the environment. It is now realised that light enters into the eye and is detected there, hence we see.

The light that enters our eyes must come from a source, e.g. the Sun or a light bulb. Thus if a person is somewhere where there is no light source it is pitch black - a deep tunnel or a cave for example. Children may not be aware of this because it is so rare to be somewhere totally devoid of light.


It is important to stress to children the danger of looking directly at bright lights, especially of course the Sun. Nobody should look directly at the Sun, not even using filters, smoked glass, sun glasses or whatever. Telescopes and binoculars are especially dangerous in this respect and must never ever be pointed at the Sun. Also be aware that if children are given a convex lens (i.e. a magnifying glass) they will almost inevitably try to start a fire with it by concentrating the Sun's rays of light onto a leaf or a piece of paper or the school or.....!

Light needs a source

So light travels from a source. The daylight has travelled to Earth from the Sun but between us and the Sun there is pace which is mostly quite empty, i.e., it is a vacuum. This must mean that light can travel through a vacuum, or in scientific jargon, light does not need a medium in which to travel.

Speed of light

Light travels VERY quickly and much faster than sound. This is why we see lightning before we hear the thunder. The lightning and thunder actually occur at the same time but it takes the sound longer to reach us than the light. If you hear the thunder at exactly the same time as you see the lightning, you are in trouble because you are exactly where the lightning has struck! Similarly, if you glance up to see an aeroplane, it is not where the sound appears to be coming from.

Light travels amazingly fast - at 3 x 108 m/s, which is 300,000,000 metres per second or roughly 186,000 miles per second!

Light is a member of the Electromagnetic Spectrum - a family which contains Gamma rays, X-rays, ultraviolet light, visible light, infra red light, radio waves, microwaves. All this family have similar characteristics, e.g. they all:

But they have varying amounts of energy, gamma rays being the most energetic and radio waves the least.

In Astronomy, distances are measured in light years.

1 light year is the distance that light will have travelled in 1 year.

As light travels at 186,000 miles per second, this is quite a long way!

It is worth considering the following facts:


Transparency, Opaque materials and shadows
Reflection of Light, Intensity
Wavelength, Colour, Filters
The eye
Assessment Material
Reference Material