Electromagnetic Radiation (EMR)
Across the whole electromagnetic (EM) spectrum (see Figure 1), only a small set of wavelengths can be detected by our eyes. This part of the spectrum is known as the visible (or optical), and covers a range from around 4000 – 7000 Angstroms. One Angstrom = 0.1 nanometres. Non-visible parts of the electromagnetic spectrum include radio waves, microwaves, infrared and ultraviolet light, X-rays and gamma-rays. All forms of EM radiation travel at the speed of light (300,000 km per second).
You may want to find out more about the electromagnetic spectrum.