Electromagnetic radiation refers to a phenomenon that moves energy from one place to another, and carries with it an electric field and a magnetic field. There are several kinds of electromagnetic radiation (radio waves, microwaves, x-rays, etc.), but light is the part we can see.

Electromagnetic radiation travels at about 186,000 miles per second (300,000 kilometers per second), so light from the sun takes about 8 minutes to go 93 million miles (149 million kilometers) to earth. If you could drive to the sun at 60 mph (100 kph), it would take you 177 years to get there! In one second, light can go around the earth 7 times!

Mixing coloured light.  Mixing coloured light gives different colours to those produced by mixing ink. Blue and red gives magenta, while all three primary colours will mix to white. This is the method of colour mixing used to create a TV picture.

Mixing paint and ink.  This chart shows how, by mixing cyan, magenta and yellow ink, many colours can be created. Cyan and yellow give green and so on. You have probably mixed yellow and blue paint to create green in the same way. All three colours should give black but, normally, a dark muddy brown is the result. This is the method of colour mixing that is used in colour pictures in books.

Due to the wave-particle duality of matter, light simultaneously exhibits properties of both waves and particles. The precise nature of light is one of the key questions of modern physics.

Light may be regarded as a flood of particles, called photons, or as a wave. In either case, it carries energy through a vacuum at a velocity which is a universal physical constant, and is the same for all observers and for all colors.

Light frequently behaves as a particle. Although individual photons all travel with velocity c, a long wavelength, low frequency photon carries little energy; while a short wavelength, high frequency photon has a high energy. Redder light has lower energy per photon; bluer light has higher energy per photon.

Light also behaves like a wave in many contexts. Either the distance between crests, (the wavelength), or the number of crests to pass the observer second (the frequency) may be used to describe the color of the light. All colors propagate with the same velocity c in vacuo. Wavelength, frequency and photon energy are all interrelated.