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The Electromagnetic Spectrum (Light)

A light wave consists of energy in the form of electric and magnetic fields which vibrate perpendicular to one another and are called the electromagnetic spectrum. The word light usually refers to the visible part of the electromagnetic spectrum. Energy in light waves is transported by particles called photons. Photons do not have any mass, but the energy they carry can be measured in terms of wavelength.

Light (or electromagnetic radiation), can be thought of as either a particle or a wave. As a wave, light has:

• a wavelength, {\lambda}(distance between two peaks)
• a frequency, {\text{f}} (number of waves passing you each second)
• a speed, {\text{c}}={\lambda}\ {\cdot}\ {\text{f}} (this is always the same: 300,000 km/s)
• an energy, {\text{E}}={\text{h}}\ {\cdot}\ {\text{f}} (where {\text{h}} is the Planck constant) Note that because the speed of light is a constant, {\lambda}, {\text{f}}, and {\text{E}} are linked: if you know one, you can easily find the other two.

The electromagnetic spectrum from shortest to longest wavelength (i.e. from most energetic to least energetic):

Gamma-ray: < 0.01 nm

X-ray: 0.01 - 10 nm

Ultra violet (UV): 10 nm – 380 nm

Visible: 380 – 700 nm

Infrared (IR): 700 nm – 1mm (700 nm – 106 nm)

Microwave: 1 mm – 1 m

Radio: > 1 m

The shorter the wavelength of light, the more energy it carries. Note that the speed of light is constant (in the entire universe) so all of those types of light will always travel at the speed of light. We usually designate the speed of light with little ‘c’ and its value is 300,000 km/s.