Discover Light Energy: Sources, Properties, and How Light Behaves

Light energy is a form of energy that you can see and that travels in waves. It is one of the most important forms of energy in your world. You can learn more about other forms of energy by exploring Heat Energy, Sources and Transfer and Sound Energy, Vibration and Sound.

Light travels in straight lines, moving faster than anything else in the universe. This is why you see a lightning flash before you hear the thunder!

A natural source of light is one that exists in nature without human help. The sun is Earth's biggest and most important natural light source it is actually a giant glowing star. Other natural sources include stars, lightning, and fireflies.

An artificial source of light is one that people create or build, like a light bulb powered by electricity, a flashlight, or a candle flame. You use artificial light every day to see when it is dark outside.

Some living things, like deep-sea fish and fireflies, make their own light through a process called bioluminescence. This is light made by living creatures through chemical reactions in their bodies.

The moon is NOT a light source it only reflects light from the sun back toward Earth. Objects that make their own light are called luminous objects. Objects that only reflect light are called non-luminous objects.

Light always travels in straight lines from its source. This is called rectilinear propagation, and it explains why shadows have sharp edges and why flashlight beams look straight.

When light hits different materials, different things can happen. You will discover three important ways materials interact with light:

• Transparent materials (like clear glass) let all light pass straight through. You can see clearly through them.
• Opaque materials (like a wooden door or a thick book) block all light. No light passes through at all.
• Translucent materials (like frosted glass or wax paper) let some light through but scatter it, so you cannot see clearly through them.

When an object absorbs light, it takes in the light energy rather than passing it or reflecting it. Dark-colored objects absorb most light, which is why they feel warmer in sunlight.

Reflection happens when light bounces back off a surface. When light hits a shiny mirror, it reflects and bounces back in a new direction. This is why you can see yourself in a mirror.

Refraction is the bending of light as it passes from one material into another, like from air into water. You can see refraction when a straw in a glass of water looks bent or broken at the surface.

A shadow forms when an opaque object blocks light from reaching a surface behind it. Shadows are always on the opposite side of the object from the light source. When you move closer to a light source, your shadow grows bigger because you block more light rays.

White light, like sunlight, is made up of ALL the colors of the rainbow mixed together: red, orange, yellow, green, blue, indigo, and violet (ROY G BIV).

A prism is a special piece of glass that bends light and separates it into all the rainbow colors. After rain, tiny water droplets in the air act like little prisms and create a rainbow in the sky. This is an example of refraction happening in nature.

The color you see on an object depends on which color of light it reflects. A red apple looks red because it reflects red light and absorbs all other colors.

Light Energy: Light energy is a form of energy that you can see and that travels in waves. It is different from heat energy, which you feel, and electrical energy, which travels through wires.

Sunlight: Sunlight is the natural light that comes from the Sun. It is the most important source of light and energy for life on Earth.

Flame: A flame is light made by burning, like the light from a candle. When something burns, it releases light and heat energy.

Glow: A glow is a soft, steady light, like the warm light from an ember or a nightlight. It is gentler than a bright flame or a lamp.

Lamp: A lamp uses electricity to produce light. It is an artificial light source that you use at home or in school.

Energy: Energy is what all light sources use or release to make light happen. Light energy is just one of many forms of energy around you.

Transparent: A transparent material lets all light pass through it, so you can see clearly on the other side. A clear glass window is transparent.

Opaque: An opaque material blocks all light from passing through it. A wooden door and a thick book are opaque, and they create dark shadows.

Translucent: A translucent material lets some light through but scatters it, so you cannot see clearly through it. Frosted glass and wax paper are translucent.

Absorb: When a material absorbs light, it takes in the light energy rather than passing it or reflecting it. Dark objects absorb most light and can feel warm in sunlight.

Reflection: Reflection is when light bounces back off a surface, like a mirror. This is how you see your own face in a mirror.

Refraction: Refraction is the bending of light as it moves from one material into another, like from air into water. A straw in a glass of water looks bent because of refraction.

Shadow: A shadow is a dark area that forms when an opaque object blocks light from reaching a surface behind it. Shadows are always on the opposite side from the light source.

Prism: A prism is a special piece of glass that bends and separates white light into all the colors of the rainbow.

Bioluminescence: Bioluminescence is the ability of some living things, like fireflies and deep-sea fish, to produce their own light through chemical reactions in their bodies.

Luminous Object: A luminous object is one that makes its own light, like the sun or a light bulb. The sun is a luminous object because it creates its own light.

Non-luminous Object: A non-luminous object does not make its own light. It can only be seen because it reflects light from a luminous source. The moon is a non-luminous object.

You can explore light properties at home or in class. Try holding a flashlight behind different materials clear plastic, wax paper, and cardboard to see which ones are transparent, translucent, or opaque.

You can also use a glass of water and a piece of white paper to see refraction. Place a pencil in the water and look at it from the side. You will notice it looks bent where it enters the water!

To learn more about how the sun moves and creates shadows at different times of day, explore Sun Movement and Daily Sun Patterns. You can also discover how plants use light by visiting Plant Responses to Light, Water, and Touch.

You have already learned about Light Properties, Sources, Reflection, and Shadows, which gives you a strong foundation for understanding light energy in more depth.

Your knowledge of Physical Properties and Observable Characteristics of Materials helps you understand why different materials interact with light in different ways. You also learned about States of Matter, Solids, Liquids, and Their Properties, which connects to how light passes through or is blocked by different materials.

Understanding Sound Properties, Volume, Pitch, and Vibration helps you compare light energy and sound energy as two different forms of energy that travel in waves.

Light energy is part of a bigger family of energy forms. You will explore Heat Energy, Sources and Transfer to compare how heat and light both come from the sun and other sources. You will also study Sound Energy, Vibration and Sound to see how sound and light are both forms of energy that travel in waves.

Understanding how light interacts with materials connects to Properties of Solids, Shape, Volume, and Structure and Properties of Liquids, Flow, Volume, and Containers, because the state of a material affects how light passes through it.

You will also connect light energy to Magnetic Forces, Attraction and Repulsion as another invisible force that acts on objects around you.

What you learn here prepares you for exciting future topics! You will explore Heat Sources, Natural and Artificial Sources and Heat Transfer, Conduction, Convection, and Radiation. You will also study Day and Night and Earth's Rotation Effects, where the sun's light plays a key role, and Magnetic Forces, Fields and Interaction.