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We Need Light to See · Light, Sound, and Heat · 1-PS4-2 · light and sight

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We Need Light to See

with Atlas

Atlas stands inside a cozy bedroom at night, holding a bright flashlight that makes a golden circle of light on a wall covered with colorful animal posters, while the rest of the room is hidden in deep shadow.

Identify that we need light to see objects around us.
Compare what we can see in a bright place versus a dark place.
Explain what happens to our ability to see when all the light goes away.
Identify everyday sources of light such as the sun, lamps, and flashlights.

Key terms

light: the brightness that lets our eyes see things
dark: when there is no light to see by
light source: anything that makes its own light, like the sun
reflect: to bounce light off a surface
vision: our ability to see things with our eyes

How We See Things

Seeing works like a little journey of light. First, light leaves a source such as the sun or a lamp. The light travels to an object and bounces off it. Then that bounced light travels into your eyes. Your eyes catch the light and your brain turns it into a picture. Without light making this trip, your eyes have nothing to catch.

Where Light Comes From

Light comes from light sources. The biggest one is the sun, which lights up the whole outdoors during the day. Indoors we use lamps, ceiling lights, and flashlights to make our own light. A phone screen and a campfire also give off light. When every light source is off and the sun is down, the room goes completely dark and we cannot see.

Worked examples

Maya is in a dark tent and wants to read her book. What should she do?

Notice the problem: there is no light, so no light can bounce off the page into her eyes.
Add a light source by turning on a flashlight.
Now light shines on the page, bounces into her eyes, and she can see the words.

Answer: She turns on a flashlight to add light so she can see.

Hi! I am Atlas. Let me tell you something really cool about your eyes. Your eyes are amazing — but they need one thing to work. They need LIGHT. When there is light in a room, you can see the toys on the floor, the colors on the wall, and your friends' faces. Light bounces off objects and travels into your eyes. That is how you see! Now imagine you walk into a room and someone turns off ALL the lights. What happens? Everything disappears! You cannot see anything at all. The objects are still there — but without light, your eyes cannot find them. Light can come from the sun outside, from a lamp in your room, or from a flashlight you hold in your hand. When we have light, we can see. When the light is gone, the dark takes over and we cannot see. Here is a hint: if you are in the dark and you want to see, you need to add light!

Activity

Sort each picture into the bucket where you could see it clearly.

Practice

Name two things that make their own light at home.

Why can you not see toys when all the lights are off?

Common mistakes to avoid

Your eyes can make their own light.Eyes do not make light — they only catch light that comes from a source and bounces off things.
If you wait long enough you can see in total darkness.In complete darkness there is no light at all, so waiting will never let your eyes see.

Check your understanding

You walk into a room and turn off all the lights. What happens?

Which of these helps you see things in a dark room?

Maya is reading a book outside on a sunny day. Why can she see the words on the page?

Recap

We need light to see. Light leaves a source, bounces off objects, and travels into our eyes so our brain can make a picture. When all the light is gone, the room is dark and we cannot see anything until we add light.

Reflect

What is your favorite source of light, and why?