1.35 Light and Dark

If you have ever wondered about the fascinating science of light, then keep reading! In this lesson, you will learn where light comes from, how it travels in waves, and what makes darkness. Without light, you wouldn’t be able to read this right now!

What is Light?

”It’s way past your bedtime! Lights out!” Oh no. Mom caught you trying to stay up late again and turned off the lamp in your room. But lucky for you, she doesn’t know that you keep a flashlight under your bed for times like these when you just have to read one more chapter! But as you turn on the flashlight and the room glows, you forget about reading your book and start to wonder…What is light?

Light is energy that travels in waves. When you think of waves, you might think of the ocean. Although light waves and ocean waves are both waves, they are different types. Light waves are electromagnetic waves while ocean waves are mechanical surface waves. Electromagnetic light waves are invisible to our eyes.

Light travels very quickly. Much of the light we see on Earth comes from the Sun, which is 93 million miles away. Even though the Sun is very far away, light traveling from the Sun can reach Earth in about 8 minutes! If we tried to take an airplane to the Sun, it would take about 19 years. Wow! Light is fast!

Light traveling from the Sun to Earth

What about the light coming from your flashlight? Or your lamp? What about the light from a candle or a campfire? Where does this light come from? Like we said earlier, light is energy. Energy is how things work, move, or change. It includes the energy you use to play at the park!

Just like the energy we use to run and jump, light is a form of energy that helps us to see. The light energy in the flashlight is being powered by a battery. The lamp in your room needs to be plugged in to use electricity to get its light energy. Just remember, all light is energy, whether it comes from the Sun, a battery, an electrical outlet, a candle, or a campfire.

1. Main points:

Light is a type of energy that travels in waves and is essential for us to see. It can come from various sources like the Sun, batteries, electrical outlets, candles, and campfires.

2. Questions:

• Content Analysis: What are the two types of waves mentioned in the text, and how are they different?
• Contextual Analysis: How long does it take for light from the Sun to reach Earth, and what does this tell us about the speed of light?
• Linguistic Analysis: What words are used in the text to describe how light helps us in our daily activities?

3. Further Discussion:

• What are some other sources of light that you can think of, and how do they produce light?

4. Answers:

• Content Analysis: "Light waves are electromagnetic waves while ocean waves are mechanical surface waves."
• Contextual Analysis: "Light traveling from the Sun can reach Earth in about 8 minutes." This indicates that light travels extremely fast.
• Linguistic Analysis: The text uses phrases like "helps us to see" and "the energy you use to play at the park" to describe the importance of light in our daily lives.

What is Dark?

To answer this question, we need to think about opposites. The opposite of big is little. The opposite of black is white. The opposite of light is dark! Dark means the absence of light, or that light is not there.

Think about your class at school. If a student is at home sick, he or she is absent. So, dark means that light is absent. The Sun’s light never actually disappears, but it is absent at nighttime. We cannot see it because Earth rotates, or spins, and we turn away from the Sun at nighttime, and the sunlight shines on the opposite side of Earth.

We can also have darkness when there is an object blocking the light. Have you ever seen someone at the beach using an umbrella on a sunny day? They are not waiting for it to rain – they are trying to block the light with the umbrella. Also, when someone turns off the electricity, like a lamp, or a battery-powered object, like a flashlight, the energy shuts down and the waves of light stop traveling. Then, we have darkness.

A beach umbrella can block sunlight and create darkness

1. Main points:

Darkness is the absence of light, occurring when light is absent or blocked by objects, during Earth’s rotation at night, or when the energy source of a light, like electricity or a battery, is turned off.

2. Questions:

• Content Analysis: What is the primary cause of darkness as described in the text?
• Contextual Analysis: How does the rotation of Earth contribute to the occurrence of darkness?
• Semiotic Analysis: What objects are mentioned in the text that can create darkness by blocking light?

3. Further Discussion:

• Can you think of any other situations where darkness occurs and why it happens?

4. Answers:

• Content Analysis: Darkness happens when "light is absent" or when "light is not there."
• Contextual Analysis: At "nighttime…Earth rotates, or spins, and we turn away from the Sun," leading to darkness on the side of Earth away from the Sun.
• Semiotic Analysis: An "umbrella on a sunny day" is used to block the light, creating a shadow or darkness underneath it.

Lesson Summary

Now that we know what light and dark mean, you will be able to notice them all around you! Light is energy that travels in invisible electromagnetic waves from its source to our eyes so we can see. We have darkness when light is blocked, like an umbrella blocking sunlight, or when light energy is shut off, like in an electric or battery-powered object. Now you know what Mom means when she says ”Lights out!”