Learn About Light Sources

Without light, we could not see anything at all. Light is a form of energy that travels outward from a source. Every light source falls into one of two groups — natural (made by nature) or artificial (made by people).

Natural light sources

• Sources that exist in nature and were not created by humans.
• The sun — by far the most important natural light source on Earth. It provides nearly all the light and heat we need to survive.
• Stars — distant suns that glow with their own light; we see them at night when the sun is not shining.
• Fire and lightning — fire gives light as it burns, and lightning is a giant spark in the sky.
• Bioluminescence — some animals such as fireflies and deep-sea fish make their own light through a chemical reaction in their bodies.

Artificial light sources

• Sources created by humans to provide light where and when needed.
• Light bulbs and lamps — electricity passes through a filament or LED and produces light.
• Candles — burning wax produces a flame that gives off light and heat.
• Screens — televisions, phones, and tablets produce their own light.
• Flashlights — portable battery-powered lights.

How light travels

• Light always travels in straight lines — it cannot bend around corners or objects.
• When light hits an opaque (not see-through, unlike transparent glass) object, it is blocked. The area behind the object where no light reaches is called a shadow.
• When light hits a shiny or smooth surface, it bounces back. This is called reflection. Mirrors reflect light very well — that is why you can see yourself in them — and the moon shines only because it reflects sunlight.