Here we focus on those scientific concepts that are the hardest to explain to children. We break it down into what pupils need to know and outline the background science. Even though much of the background science does not need to be taught to primary aged children, it is useful for you as a teacher when addressing misconceptions and children’s challenging questions.

Please refer to your national curriculum documents when planning your sequence of work and ensure that you teach the correct knowledge for your year group.

What do children need to know about light?

Learning about light should be as exploratory, hands-on and pupil-led as possible. We have included some ideas for how to teach light in part two of this topic guide.

Key scientific concepts: Pupils need to...

1. Recognise that light from all light sources, natural and artificial, travels in straight lines.
2. Recognise that light can travel through some materials while others might block or reflect light.
3. Recognise that light is needed to see things and that dark is the absence of light, eventually using the idea that light travels in straight lines to explain that objects are seen because they either give out or reflect light into our eyes. (In Scotland pupils need to explain how the human eye works.)
4. Understand that light from the Sun is harmful and there are ways to protect our eyes and skin.
5. Know that materials that do not let light travel through them will cast shadows and describe factors that affect the size of the shadows formed, eventually being able to use ideas about light travelling in straight lines to explain why shadows have a particular shape.

1. Light, from all light sources, travels in straight lines.

Pupils need to know:

• Luminous objects such as lamps, flames and the Sun are sources of light, some are natural and some artificial.
• Light is given out from a light source.
• Light travels out in straight lines in all directions from a light source.
• Darkness is the absence of light.

Background Science for Teachers:

Natural light comes from sources that are naturally occurring such as the Sun, lightning, bioluminescence, and stars. Artificial light comes from human made devices that would not occur naturally in nature such as light bulbs, lasers, candles and LEDs.

The light rays that leave a light source will travel in straight lines in all directions until they meet a material that changes their path. Some materials may stop light whereas others might allow light to travel through in a straight line. Other materials may scatter light rays in different directions, reflect light rays or even change the speed of the light rays which can cause the rays to change direction.

In secondary school and beyond pupils will go on to learn that light rays are transverse, electromagnetic waves that travel at the speed of light (300,000,000m/s). They will learn that light waves have other attributes such as amplitude which affects the brightness of the light and frequency which affects the colour of the light. They will begin to use mathematical relationships to describe the behaviour of light waves.

For primary aged pupil it is helpful for pupils to link their learning about light to observations in the real world. This can be achieved with the use of photographs showing different examples of light travelling in a straight line. In addition, you can use single beam torches for children to see how the light travels in a straight line.

From right to left-

Top row: A Hong Kong skyline and a lighthouse shining out to the sea through thick mist.

Bottom row: Sun rays breaking through some clouds and a laser show. 

Image credits: Hong Kong Skyline by Ken Eckert​ CC BY SA, Sun rays by Matthew Bowden via Canva,​ Laser show by Fir0002/Flagstaffotos​ CCBy-NC or if commercial GFDL v1.2, Through the Fog by JamieZink via Canva

2. Light interacts differently with different materials.

Pupils need to know:

• Some materials will let light through whilst others block some or all of the light.
• Materials that are transparent let all light pass through, translucent materials block some of the light and opaque materials block the light completely.
• Some objects and materials are very reflective and appear bright or shiny.
• Some objects and materials appear dull because they only reflect some of the light that hits them and absorb the rest.

Background science for teachers:  

When light rays hit an object, they may; pass straight through (transmit), bounce off (scatter or reflect) or be stopped (absorb) – or a combination of these.

A transparent material allows all light rays to pass through in a straight-line whereas an opaque material will not allow any light rays to pass through. The idea of a translucent material is quite difficult to explain and can lead to misconceptions being formed if not addressed with care. A translucent material only lets through some of the light rays but why this happens is complex and depends on the specific material, some of the light may be scattered in different directions. Some might be absorbed, and some might be reflected from the surface and therefore not pass through.

Pupils may think that there are no light rays coming from non-luminous objects but any non-luminous object that you can see is reflecting light, but this light is usually scattered in all directions.

Shiny materials such as a mirror are highly reflective, all the light that hits the smooth, flat surface at right angles reflects back towards the light source. This can be demonstrated using a tennis ball – bounce the ball at right angles to a surface and see it come back along the same line. This guidance from the PSTT is useful. Highly reflective materials keep us safe on the roads when used in cats’ eyes and high visibility clothing. The light from a car’s headlights hitting a reflective material worn by a cyclist will reflect straight back to the driver’s eyes and can be seen up to 100 metres away in darkness. Some highly reflective fabrics are cloth that is coated with micro-glass beads which are half coated with aluminium to make them even more reflective.  

3. We need light to see.

Pupils need to know

• We see things when light goes into our eyes.
• Without light we cannot see anything.
• Light can travel from a light source straight to our eyes or might travel from the source to an object, reflect off that object and then travel into our eyes.

Background Science for teachers:

Our eyes have light sensitive cells inside them and they work by detecting that light and sending signals to our brains. We only see things when light travels into our eyes and when there is no light at all, it is dark and we can not see anything. If your curriculum (Scotland) requires a deeper understanding of how the human eye works, BBC bitesize has this guide.

When we see a light source light, light travels in straight lines directly from the light source and into our eyes. Applying this idea to explain how we see can be very tricky for pupils and it is possible that misconceptions might arise. This can be shown with a scientific diagram where the light ray is shown as a straight pencil line drawn with a ruler and an arrow showing its direction. Simple ray diagrams are an opportunity for children to develop their skills in drawing scientific diagrams and using these to explain scientific ideas about light.

Light from a light bulb travelling to the eye. 

Image credit: The Ogden Trust. Licensed only for use on Explorify.

Pupils are even more likely to form misconceptions when it comes to explaining how we see objects that are not light sources. In this case the light from a light source is reflected from the surface of the object, then travels into our eyes. The light still travels in a straight line into our eyes and can also be shown using a simple light ray diagram as shown.

Light reflecting off a book and travelling to the eye. 

Image credit: The Ogden Trust. Licensed only for use on Explorify.

4. Light from the Sun is harmful.

Pupils need to know:

• Light from the Sun includes some very harmful light rays that can damage our eyes.
• Some materials block this harmful light, while letting less harmful light through, these materials are used in the lenses of sunglasses to protect our eyes.
• The materials that are used to make sunblock and sun cream block harmful light rays in sunlight, this helps to protect our skin from the dangers of sunlight.

Background science for teachers:

The Sun, our nearest star, is a natural light source that radiates light towards the Earth. Part of sunlight is made up of invisible ultraviolet (UV) light. Although we cannot see UV light, it can damage our eyes. Long term exposure to sunlight can permanently damage the retina at the back of the eye.

While the atmosphere around our planet has a layer of gas that absorbs a large proportion of the dangerous light from the Sun, some still passes through to us on Earth. We can protect our eyes by wearing sunglasses that let some of the visible light through but block the dangerous UV light. Most sunglasses today are made from special materials that have UV protection embedded in the lens or as a coating on the front of the lens. Some older sunglasses and fashion sunglasses with dark lenses block some visible light so you don’t need to squint but they do not block the dangerous UV light. 

Sunblock and sun cream work in a similar way. They contain materials that absorb some or all of the dangerous UV light so that it is not absorbed by our skin which can lead to sunburn and permanent damage.

5. Materials that block some or all light create shadows.

Pupils need to know:

• When an object blocks the light from a light source, a shadow is formed.
• The shadow is the area which light from the light source cannot reach. 
• You can explain and predict the position, shape and size of shadows by drawing a scientific diagram showing some light rays travelling in straight-lines from the source then hitting the edges of an opaque object placed in front of it.
• Because light always travels in straight lines, the shape of a shadow is the same shape as the object that blocks the light. 

Background science for teachers:

Light travels in straight lines. When light hits an opaque object, it is blocked and, therefore the area behind the object becomes dark. This is called a shadow. Totally transparent objects do not create shadows because light passes straight through them. Opaque objects make dark shadows. Translucent objects make faint shadows.

The size of the shadow depends on the distance between the object and the surface on which it appears. If the screen is moved further from the object, the shadow gets bigger. The diagram below shows light rays as lines that come from a light source, with arrows showing the direction in which the light is travelling. This idea helps us explain and predict the position of shadows. 

Diagram illustrating how a shadow is formed. 

Image credit: The Ogden Trust. Licensed only for use on Explorify.

The shape of a shadow is always determined by the shape of an object. When light hits an object at different angles, its shadow may appear stretched or squashed compared to what we see as the object’s shape.

Image illustrating how the angle at which light hits a tree will affect the length of its shadow. 

Image credit: The Ogden Trust. Licensed only for use on Explorify.

If the light source moves relative to the object, then the size and/or position of the shadow will change. Each day the Sun rises in the east, appears to move across the sky and then sets in the west – this happens because the Earth is spinning on its axis.  

Image illustrating the movement of the sun between sunrise and sunset.

Image credit: The Ogden Trust. Licensed only for use on Explorify.

Useful related resources

Ogden Trust- Phizzi enquiry: shadows 

Ogden Trust- Phizzi Focus: using technology explains how apps and dataloggers can be used to investigate light.

Ideas to try with your class 

Now you've got the tricky scientific concepts under your belt, try our ideas to help you explore light with your class in a way they will understand in part two of this topic guide. You can also take a look at the related topic guides for electricity, materials, Earth & space, sound, animals including humans, living things and their habitats and plants.

Many thanks to the Ogden Trust, who have collaborated with Explorify to produce this 'Tackle the tricky bits' page.

Image credit: Untitled by tommyvideo from Pixabay via Canva