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What is light?
Light is produced by luminous objects, such as fires, electric lamps and stars like the Sun. The light that we can see is called visible light, but there is also light that we cannot see, including ultraviolet light and infrared light. This section is all about visible light.
Extremely fast
If you switch on an electric lamp, the light seems to come on instantly. However, the light doesn't really reach your eyes in no time at all. It just takes an extremely short time, because light travels extremely quickly. Light travels very much faster than sound, which is why you see lightning in a thunderstorm before you hear the thunder clap.
Straight lines
Light travels in straight lines. It cannot bend around corners, so we cannot see around a corner unless we use a mirror. We get shadows because light cannot bend round behind an object. When the Moon moves between the Sun and the Earth, it casts a shadow or "umbra" on the Earth. This blocks or partially blocks our view of the Sun, and it is called a solar eclipse.
Light travels at 300 million m/s
Light and objects
Light cannot travel through opaque objects, such as brick walls. Opaque objects can cast dark shadows when light is shone on them. Light travels through transparent objects, such as glass windows. Paper and other translucent objects let some light through, but not all of it. This is why you can see the typing on the other side of a piece of printed paper if you hold it up to a light.
Light can travel through a vacuum such as space, but sound cannot. Science fiction films often show explosions in space with loud bangs. In real life, you would see the explosion but not hear it.
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