All about light

Let's learn what light is and how it travels.

Light is a form of energy. It can come from many sources, for example:

• the Sun
• light bulbs
• lightning
• candles
• glow sticks.

Some animals, such as fireflies and glow-worms, are also light sources. They make their own light to attract mates to breed with.

• light reflects off things and enters our eye through the pupil.

• it passes through the lens which focuses the light onto the retina in the back of the eye.

• from here, light sensors transform the light hitting them to electrical signals that travel through the optic nerve to the brain.

• the brain interprets these signals into images of what we can see.

This is how we 'see'.

Daylight from the Sun might look like it's white but light is made up of many colours. We call this full range the colour spectrum.

We can see the full colour spectrum in a rainbow.

A rainbow is formed when sunlight bends when it enters raindrops. This splits white light into the different visible colours that are then reflected back out of the raindrops.

We can split white light into a spectrum of colours using glass prisms or the reflective side of a CD.

Different surfaces reflect different parts of the spectrum.

For example:

A red object absorbs every colour in the colour spectrum apart from red, which it reflects.

A yellow object absorbs every colour in the colour spectrum apart from yellow, which it reflects.

Black is a little different. A black object absorbs all the colours of the colour spectrum so it doesn’t reflect any colour.

Most objects we think of as black aren't truly black. They are more usually very dark colours that reflect a little bit of light.

Light travels in straight lines from the source.

It reflects off objects in straight lines as well. This is how a smooth, shiny mirror reverses what you see.

When light reflects off a rough surface it goes in different directions so you don’t get a sharp reflection.

Think about how different a reflection is in still water compared to water that has waves or ripples.

Light reflecting off this still water makes the house look like it's sitting on a mirror.

Reflections on rippled water usually looked twisted and distorted.

Light travels in straight lines until it passes from one material to another, for example from air to water or water to air.

When this happens, the light is refracted, which means it changes speed. This can change the direction of the light, causing objects underwater to look bent or like they don't line up properly.

Light travels incredibly fast. In fact it’s the fastest moving thing in the universe – nearly 300,000 km in 1 second!

It is so fast that it can travel 7 ½ times the length of the Equator in one second!

Astronomers use light years to measure really big objects and long distances in the Universe.

Our galaxy, the Milky Way, is over 100,000 light years across. That means if you could travel at the speed of light, it would take you 100,000 years to get from one side to the other!

light energy – The form of energy that allows us to see objects around us.

light source – Anything (natural or artificial) that produces light.

colour spectrum – The range of different colours seen when white light is split up.

refraction – The process of light changing speed as it travels through different materials. This can cause it to change direction.

Try this light experiment!

You will need:

• a coin

• a glass filled with water

• a paper straw or pencil

Fill the glass with water and experiment with how this changes how the coin, straws and pencils look.

Watch this video to find out what to do!

Do you want to find out how much you've learned about light? Try our fun quiz!