Wavelength

Wavelength is the spatial period of a repeating wave: the distance over which its shape repeats. For electromagnetic radiation in vacuum, it determines frequency through the speed of light.

Spectral power distribution: A spectral power distribution describes radiant power as a function of wavelength or frequency. It uses wavelength to show where a source’s radiated power lies across the spectrum.
Wave equation: The wave equation is a differential equation describing how waves propagate through space and time. Its traveling-wave solutions have a spatial period identified as wavelength.
Spectroscopy: Spectroscopy studies how matter interacts with electromagnetic radiation as a function of wavelength or frequency. Wavelength-resolved measurements reveal characteristic absorption and emission features.
Period: The period of a repeating process is the time required for one complete cycle. It measures repetition in time, whereas wavelength measures repetition in space.
Wavenumber: Wavenumber is spatial frequency, commonly expressed as cycles per unit distance or radians per unit distance. It expresses the same spatial scale as wavelength in reciprocal form.
Speed of light: The speed of light is the propagation speed of electromagnetic radiation in a specified medium. Dividing propagation speed by frequency gives wavelength in that medium.
Spectrophotometry: Spectrophotometry measures how much light a sample transmits or absorbs across selected wavelengths. Its wavelength settings determine which parts of a sample’s spectrum are measured.
Amplitude: Amplitude is the maximum displacement or field strength of a wave from its equilibrium value. It describes wave magnitude, not the distance between repeating points.
Frequency: Frequency is the number of cycles of a repeating event or wave per unit time. For electromagnetic radiation, frequency and wavelength are linked by the wave’s speed.
Refraction: Refraction is the change in direction of a wave as its propagation speed changes across a boundary. Frequency stays fixed at a boundary while wavelength changes with speed.

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