Science
What is light?
Quick answer
Light is a form of energy that travels in straight lines, very fast. We see things when light from them enters our eyes, either because they make light or because they reflect it.
In one sentence
Light is energy that travels in straight lines from a source, and we see things when that light reaches our eyes.
Explained
Some things make their own light. These are light sources: the Sun, stars, fire, torches, lamps and screens. Most things don't make light. We see them because light from a source bounces off them, which is called reflection, and travels into our eyes.
Light travels in straight lines. That is why you can't see round corners and why shadows form when something blocks the light.
Light is incredibly fast: about 300,000 kilometres every second. It could go round Earth about seven times in one second. Even so, the Sun is so far away that its light takes about 8 minutes to reach us.
When light hits a surface, a few things can happen:
- Shiny, smooth surfaces like mirrors reflect it neatly, so you can see a reflection.
- Transparent materials like clear glass let most light through.
- Translucent materials like tissue paper let some through, blurrily.
- Opaque materials like wood block light completely.
White light is actually a mixture of colours. When sunlight passes through raindrops or a glass prism, the colours bend by different amounts and spread out into a rainbow: red, orange, yellow, green, blue, indigo and violet.
Examples
| Light source | Reflects light only |
|---|---|
| Sun | Moon |
| Candle flame | mirror |
| Torch | white paper |
| Firefly | bicycle reflector |
sun
lamp
candle
moon
Common mistakes
- "The Moon is a light source." The Moon reflects sunlight; it makes no light of its own.
- "Our eyes send out light to see." Light travels into our eyes, not out of them. In total darkness, you see nothing.
- "Black is a colour of light." Black is what we see when no light, or very little, reaches our eyes from something.
Quick quiz
Light
Check what you know with 4 quick questions.
Question 1 of 4
How do we see a book in a lit room?
Practise it
Try it
Use a mirror and a torch to bounce a beam of light onto a target, and see how your eyes use light in the senses. Then try more physics activities.
Light and physics activities
For grown-ups
Related topics
Shadows
A shadow is a dark area made when an opaque object blocks light. Because light travels in straight lines, it cannot bend round the object, leaving a dark shape behind it.
The senses
The five main senses are sight, hearing, smell, taste and touch. Sense organs such as the eyes, ears, nose, tongue and skin collect information and send it to your brain.
The solar system
The solar system is the Sun and everything that orbits it, including eight planets, their moons, dwarf planets such as Pluto, asteroids and comets.
Photosynthesis
Photosynthesis is how green plants make their own food. They use energy from sunlight to turn carbon dioxide from the air and water from the soil into sugar, giving out oxygen.
Sound
Sound is made when something vibrates. The vibrations travel through air, water or solids to our ears. Sound cannot travel through empty space.
The Moon
The Moon is Earth's natural satellite, a rocky ball about a quarter of Earth's width that orbits us roughly once a month. It shines by reflecting sunlight.