Visible Light

How they're made

Our eyes can detect only a tiny part of the electromagnetic spectrum, called visible light.

This means that there's a great deal happening around us that we're simply not aware of, unless we have instruments to detect it.

Light waves are given off by anything that's hot enough to glow.

This is how light bulbs work - an electric current heats the lamp filament to around 3,000 degrees, and it glows white-hot.

The surface of the Sun is around 5,600 degrees, and it gives off a great deal of light.

White light is actually made up of a whole range of colours, mixed together.

We can see this if we pass white light through a glass prism - the violet light is bent ("refracted") more than the red, because it has a shorter wavelength and is slowed down more by the glass - and we see a rainbow of colours.

This is called 'dispersion', and allows us to work out what stars are made of by looking at the mixture of wavelengths in the light.

Cinema projectors use a powerful lamp

This filming lamp has a 'colour temperature' of 3000K

Uses

We use light to see things!

As the Sun sends so much light towards our planet, we've evolved to make use of those particular wavelengths in order to sense our environment.

Compact Discs are read by laser light

Light waves can also be made using a laser. This works differently to a light bulb, and produces "coherent" light.

Lasers are used in Compact Disc & DVD players, where the light is reflected from the tiny pits in the disc, and the pattern is detected and translated into sound or data.

Lasers are also used in laser printers, and in aircraft weapon aiming systems.

To find out more about laser printers, see:
http://computer.howstuffworks.com/laser-printer1.htm

Dangers

Too much light can damage the retina in your eye.

This can happen when you look at something very bright, such as the Sun.

Although the damage can heal, if it's too bad it'll be permanent.