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An introduction to light as a form of energy and the difference between natural and artificial light sources.
Have you ever wondered why you can't see your favorite toys in a pitch-black room, even though they are right in front of you? Where does the 'stuff' that lets us see actually come from?
Light is a form of energy that our eyes can detect. It is amazing because it travels faster than anything else in the universe! In space, light moves at a speed of about kilometers per second. Light usually travels in straight lines called rays. Because light is a form of energy, it can be changed into other forms, like heat when the sun warms your skin. Without light energy, the world would be a dark, cold place where nothing could grow and no one could see.
Quick Check
True or False: Light is a form of matter, like a liquid or a solid.
Answer
False. Light is a form of energy, not matter.
We can group light sources into two main categories. Natural light sources are found in nature and are not made by humans. The most important natural source is the Sun. Other examples include stars, lightning, and even some animals like fireflies! Artificial light sources are man-made. These include things like lightbulbs, flashlights, neon signs, and the screen you are reading this on right now. Humans created artificial light so we could see and work even after the sun goes down.
Let's look at three items and decide if they are natural or artificial: 1. The Moon: Wait! The moon actually doesn't make its own light (we will learn why soon). 2. A Campfire: This is Natural because fire is a chemical reaction found in nature. 3. A Smartphone Screen: This is Artificial because it uses electricity and human-made parts to glow.
Quick Check
Is a flashlight a natural or artificial light source?
Answer
Artificial, because it is a man-made tool.
Objects are only visible if they give off their own light or if light bounces off them. Objects that create their own light are called luminous. However, most things around you—like your desk, your dog, or a tree—are non-luminous. You see them because light from a source hits them and reflects (bounces) into your eyes. Think of it like a rubber ball bouncing off a wall. If there is no light source to bounce off the object, no light reaches your eyes, and the object stays 'invisible' in the dark!
Why does the Moon look bright at night if it isn't a light source? 1. The Sun is a luminous star that creates light energy. 2. The Sun's light rays travel through space and hit the surface of the Moon. 3. The Moon acts like a giant mirror and reflects that sunlight toward Earth. 4. Even though the Moon is non-luminous, we see it because of reflected light!
What is the primary reason we can see a non-luminous object like a book?
Which of the following is an example of a natural light source?
Light is the fastest moving thing in the universe.
Review Tomorrow
In 24 hours, try to explain to a friend the difference between a 'luminous' object and a 'non-luminous' object using the Moon as an example.
Practice Activity
Go on a 'Light Hunt' around your home. List 3 natural light sources and 3 artificial light sources you can find.