Wavelength

• While wavelength can be measured from any point on a wave, it is often simplest to measure from the peak of one wave to the peak of the next, or from the bottom of one trough to the bottom of the next, ensuring the measurement covers a whole wave cycle.
• The wavelength of an electromagnetic wave is usually given in metres.
• The wavelength of visible light is typically measured in nanometres, with 1,000,000,000 nanometres making up a metre.
• Each type of electromagnetic radiation – such as radio waves, visible light, and gamma waves – corresponds to a specific range of wavelengths on the electromagnetic spectrum.
• As energy increases, frequency also increases and wavelength decreases. Therefore, shorter wavelengths correspond to higher energy levels, and longer wavelengths correspond to lower energy levels.

Wavelength & the Visible Spectrum

• The visible part of the electromagnetic spectrum consists of a range of wavelengths that correspond with all the different colours we see in the world.
• The visible spectrum, which spans wavelengths from approximately 400 to 700 nanometres, is commonly described in terms of bands of colour—red, orange, yellow, green, blue, indigo, and violet. However, these divisions are somewhat arbitrary since the spectrum is continuous, and the exact wavelength boundaries between colours is subjective.
• Humans don’t see the wavelengths of visible light directly but do see the specific colour associated with each wavelength and the colour produced when different wavelengths mix.
• The visible spectrum encompasses all the colours from red to violet, with each colour corresponding to a single light wavelength.
• The concept of colour is a perceptual property, not a property of light itself. It’s how our brain interprets the wavelengths of light that reach our eyes.
• The perceived colour (hue) of a light stimulus is dependent on its wavelength.
• A colour produced by a single wavelength is known as a pure spectral colour.

Wavelength & Colour

• Light that we perceive as white when it is reflected towards an observer contains a mix of different wavelengths of light.
• Light that contains wavelengths corresponding with red, green and blue appear white when it is reflected off a neutral-coloured surface.
• Light is seldom made up of a single wavelength. It is typically a mix of many different wavelengths that together determine the colour an observer sees as they reflect off a surface.
• The greater the number of different wavelengths incident light contains, the lower the saturation of the reflected colour. So a light comprising mixed wavelengths tends to produce lighter (whiter) colours.
• Wavelengths matching the colours of the visible spectrum are typically measured in nanometres. Hence, there are 300 distinct colours between 400 nanometres (violet) and 700 nanometres (red). If picometres are the unit used to measure wavelength then there are 300,000 different wavelengths in the visible spectrum, each corresponding to a unique colour.