Lesson 17.3: The Sun is the source of most visible light

Lesson Focus

This lesson explores the diverse origins of light. We will investigate natural sources like the Sun, the fascinating process of bioluminescence in living things, and the evolution of human-made lighting technologies from fire to modern LEDs.

Learning Objectives

• Explain how natural sources, like the Sun, produce light through the process of incandescence.
• Describe how living organisms create their own light through a chemical process called bioluminescence.
• Compare different human lighting technologies, such as incandescent bulbs, fluorescent lights, and LEDs.

The Sun shines because its high temperature makes it glow, a process called incandescence.

This light provides the energy for almost all life on Earth, enabling vision and photosynthesis.

While other stars are also incandescent, they are too far away to significantly light our world.

Some organisms glow without getting hot, a phenomenon called bioluminescence.

This is a type of luminescence where chemical reactions inside a living thing produce light.

For example, fireflies flash light patterns to find mates.

Incandescent bulbs work by passing electricity through a thin wire, or tungsten filament, until it becomes hot enough to glow.

This is an example of incandescence. However, this method is inefficient because most of the electrical energy is lost as heat instead of being converted into useful visible light.

Fluorescent lights use a two-step process called fluorescence.

First, an electric current energizes mercury vapor, causing it to emit invisible ultraviolet (UV) light.

Then, a phosphor coating inside the bulb absorbs this UV energy and emits it as visible light.

Light Emitting Diodes (LEDs) are a modern lighting technology that uses a solid semiconductor to convert electrical energy directly into light.

This process does not require filaments or gases and produces very little heat.

As a result, LEDs are highly efficient, durable, and are quickly replacing older lighting types.