e.g Red has the longest wave-length and violet has the shortest wave-length

To make a rainbow the raindrops/water vapour act as the prism and the light forms a rainbow 

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

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.

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 is more serious it can lead to blindness or eye cancer

http://www.nasa.gov/topics/technology/features/webb-beyond-vis.html