Seeing needs light
Your eyes only catch light that arrives. With no light, nothing arrives, so you see nothing.
Step 1: Something to Notice
Watch first. The explanation comes later.
You go into a room at night and cannot see your toy. Somebody turns the light on and there it is, exactly where it always was.
The toy never moved. So what changed?
Step 2: Find Out
Start bright. Then turn the lamp down step by step and watch the toy.
Step 1 — Predict
The lamp is turned all the way off. What will you see?
Choose what you think will happen. You cannot see the experiment until you do — guessing first is what makes it worth watching.
Step 3: So Here Is Why
Now the explanation, after you have seen it happen.
Light bounces
Light leaves the lamp, lands on the toy, and bounces into your eye.
It is still there
Turn the light off and the toy is still there. Reach out and you can touch it.
Where light comes from
A few things make their own light: the Sun, a lamp, a fire. Everything else passes it on.
Step 4: A Common Mistake
Lots of people think
“If you wait in a dark room, your eyes get used to it and you can see.”
Step 5: Why the Moon Shines
The same idea somewhere new.
The Moon does not make any light of its own. Sunlight lands on it and bounces off to us. That is why we can see it at all.
Step 6: Think It Through
Practice makes it stick.
The Bedroom
Problem 1 of 1
The light is off and the room is dark. Where is your teddy?
Light and Seeing
1 of 3
In which picture can you see the toy?
2 of 3
You wait a long time in a completely dark room. What happens?
3 of 3
Put each picture in the right box.
Tap something to move it.
- Empty
- Empty
Step 7: Quick Check
Show what you know.
Question 1 of 1
What do you need before you can see something?
What You Found Out
- You need light to see.
- Light lands on a thing and bounces into your eye.
- In the dark, things are still there. You just cannot see them.
For the grown-up
Light has to reach the thing — You can only see something if light bounces off it and goes into your eyes. In a room with no light at all, the things are still there — but nothing bounces off them, so you see nothing.
Your eyes do not send out light — Many people think seeing works like a torch shining out of your eyes. It does not. Your eyes only catch light that arrives. That is why a torch helps and staring harder does not.
Seeing needs light — Your eyes cannot make anything appear on their own. They work by catching light that arrives. In a room with no light at all, nothing arrives, so you see nothing — no matter how wide you open them or how long you wait.
Light bounces — Seeing takes a journey with three parts. Light leaves the Sun or the lamp. It travels until it lands on the toy. It bounces off the toy and goes into your eye. Break the journey anywhere — no lamp, or something in the way — and you stop seeing.
It is still there — Turn the light off and the toy does not go anywhere. Reach out and you can still touch it. Only the light has gone, so nothing bounces off it to your eye. Not seeing something is not the same as it not being there.
Where light comes from — A few things make light of their own: the Sun, a lamp, a torch, a fire. Everything else only passes light on. The Moon makes none at all — sunlight lands on it and bounces off to us, which is exactly what a toy on the carpet does.