What is Light?

The Sun and White Light

Look up at the sky on a sunny day. Do not look right at the sun! The light from the sun looks plain. It looks white. It might look a little yellow. We call this sunlight white light. But white light hides a big secret. It is not just one color. White light is a mix of many different colors.

Think about a big box of crayons. You have red, blue, green, and yellow crayons. You can draw a red apple. You can draw a blue sky. You can draw with each color alone. Now imagine spinning all the crayons on a fast wheel. Your eyes will see the color white. Light works in a very similar way. White light holds many colors inside it.

Isaac Newton and the Glass Prism

A long time ago, a smart man studied light. His name was Isaac Newton. He wanted to know about colors. He did a famous test with a glass toy. People call this glass toy a prism. A prism is a clear block. It has flat sides. It looks like a shiny triangle.

Newton let a tiny beam of sunlight into a dark room. He put the glass prism in front of the light. The white light went into the glass. A beautiful rainbow came out the other side!

In plain terms: Newton proved a big idea. White light holds many colors mixed together. He also showed a neat trick. A glass triangle can split the colors apart.

How a Prism Works

How does the glass prism do this? Light travels through the air in straight lines. Glass is thicker than air. Light hits the thick glass. The light slows down. This makes the light bend. Scientists call this bending dispersion 1.

Here is the magic part. White light has different colors inside it. Each color bends a different amount. Red light bends just a little bit. Violet light bends a whole lot. The glass prism spreads the colors out. The white light splits into a wide band.

You can see the colors in order:

• Red is at the top.
• Orange and yellow come next.
• Green is in the middle.
• Blue and violet are at the bottom.

Making White Light Again

Can we put the colors back together? Yes, we can! Newton did this too. He took the rainbow of light. He passed it through a second glass prism. The colors bent again. They mixed back together. They turned into plain white light 2.

Scientists still use this trick today. They use very bright lights. People call these lights lasers. Scientists mix different color lasers together. They mix red, green, blue, and yellow lasers. This mix makes a perfect white light 3.

Think about baking a cake. You start with flour, sugar, and eggs. These are all different things. The flour is white. The egg yolks are yellow. You mix them in a bowl. You bake them in the oven. You get one whole cake. White light is like that cake. The different colors are the ingredients.

Rainbows in the Sky

You do not need a glass prism to see colors. Nature makes its own prisms. Think about a rainy day. The sun comes out. It is still raining. The sky fills with tiny drops of water.

Each water drop acts like a tiny glass prism. The sunlight goes into the water drop. The water bends the light. The white light splits into many colors. This makes a giant rainbow in the sky!

People noticed this a very long time ago. A man named Robert Grosseteste wrote about rainbows. He lived in the 13th century. He wrote a book called De iride.

In plain terms: Grosseteste knew about clear shapes. He knew they can bend light. He saw a curved shape in the sky. He knew bending light makes this curved rainbow shape.

We see these beautiful colors everywhere. This happens because of how light works. White light is never just plain white. It is a hidden rainbow. Soon, we will learn the exact names of all the colors in a rainbow!

Key Terms

• White light 2 — Light from the sun or a lamp that looks plain but actually holds many different colors inside it.
• Prism 2 — A clear glass block with flat sides that can bend light and split it into a rainbow.
• Dispersion 1 — The bending and spreading of light as it passes through a thick material like glass.