Everyday Life & Technology
How does a mirror redirect light?
A ray of light meets a mirror. Where does its new path lead?
The short answer
A mirror reflects light in an orderly way. You see an object in it when light from the object reaches your eye through reflection. The mirror does not need to produce its own light.
Light paths at a mirror
1. Light reaches the mirror
The red block is in front of the mirror, the blue line. The arrow shows light travelling from the lit block to the mirror. The mirror does not make this light itself.
2. Equal angles
The dashed horizontal line is perpendicular to the mirror: it meets it at a right angle. The two red angle arcs are equal. The upper arrow shows incoming light and the lower one reflected light. Sending light back like this is called reflection.
3. An image seems to be behind it
The real light path goes from the block via the mirror to the eye at lower left. If we extend the returning path backwards in our imagination, it leads to the apparent image: the dashed block on the right.
Solid arrows show the light path. The dashed line behind the mirror is only an imaginary extension; this ray does not travel there.
The image is called virtual: it appears there, but there is no second block behind the mirror. These sketches show selected rays at a flat mirror.
How does the mirror redirect light, and why do I see another block?
Light reflects from the smooth surface. Its angles to the perpendicular line are equal. When light from the block reaches your eye via the mirror, its image appears behind the mirror. The real block stays in front.
An imagined Wusel scene
Puschel and Flauschi investigate
Puschel draws an arrow from the eye to the mirror. Flauschi asks where the light comes from. Together they trace the path from the lit object to the mirror and then to the eye. He reverses his first arrow.
Try explaining it
Which light path lets you see an object in a mirror?
Choose a), b) or c), then explain your choice.
- a)Object → mirror → eye.
- b)Eye → mirror → object.
- c)Object → eye → mirror.
Show the explanation
Correct: a): Object → mirror → eye.
A mirror reflects light in an orderly way. You see an object in it when light from the object reaches your eye through reflection. The mirror does not need to produce its own light.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
Understand step by step
How it works – simply explained
Light comes from the object
A toy is visible in a mirror when light from it reaches the mirror. The mirror does not create image light.
The smooth surface redirects
Reflection is orderly. Incoming and outgoing angles are equal relative to an imaginary perpendicular line. This line is only a drawing aid.
Your eye interprets the path
Reflected light reaches your eye. The image appears behind the surface; the toy has not actually travelled through the mirror.
Why the toy seems to stand behind the mirror
Light from the toy reflects towards your eyes. The brain interprets it as coming from behind the surface. This apparent position is called a virtual image: no actual toy is there to pick up. Reflection changes the light path, not the toy’s location.
References for this explanation: [1]
The key points again
Discovery 1
A smooth mirror reflects light in an orderly way.
Source: [1]
Discovery 2
The incoming and outgoing angles, measured from a line perpendicular to the surface, are equal.
Source: [1]
Discovery 3
A mirror makes no light of its own. Light from an object must reach your eye through the mirror.
Source: [1]