Facts At Your Fingertips: Energy and forces – Light
Light is the only form of electromagnetic radiation we can see. Most things absorb and reflect light, but few objects give out light.
The Sun is the main source of light in the day, while electric lights provide illumination at night.
Making shadows
Some materials, such as glass, allow light to pass through them. They are known as transparent. Other materials, such as wood or metals, do not let light pass through.
They are known as opaque. If something blocks the path of light, it creates a dark area behind called a shadow.
Speed of light
In a vacuum (a space that is empty of all matter), light travels at 186,000 miles (300,000 km) per second. Nothing in the universe can travel faster.
The distances of very far-off objects, such as stars and galaxies, are calculated using the distance light can travel in a year. This distance is known as a light-year. One light-year equals about 6 trillion miles (10 trillion km).
Bending and reflecting
Light normally travels in straight lines. When light travels from one material to another, such as when it passes from air to water, its path is bent, or refracted. This can create a distorted image.
Light is also bounced, or reflected, by a shiny surface, which sends light back at the same angle at which it hits the surface.