Spectrophotometer

An instrument that measures how much light a sample absorbs or transmits at selected wavelengths. Its measurements can reveal a sample’s concentration or optical properties.

Beer–Lambert law: A relationship linking a solution’s absorbance to its concentration, path length, and molar absorptivity. It connects measured absorbance to concentration when the sample follows the law’s assumptions.
Electromagnetic spectrum: The full range of electromagnetic radiation, arranged by frequency or wavelength. Spectrophotometers operate over selected regions of this broader range.
UV–visible spectroscopy: A spectroscopic method that measures absorption of ultraviolet and visible light by a sample. It is the common analytical method performed with UV–visible spectrophotometers.
Fluorometer: An instrument that measures light emitted by a sample after it absorbs excitation light. It detects emitted light, whereas a spectrophotometer typically measures transmitted light.
Monochromator: An optical device that selects a narrow wavelength band from a broader spectrum. It isolates the wavelength at which the sample is measured.
Wavelength: The distance between successive corresponding points of a wave, such as adjacent peaks. The selected wavelength determines which optical transitions or materials affect the measurement.
Colorimetry: The measurement of color through quantified responses to light across selected wavelength bands. Visible-light absorbance measurements can quantify colorants and colored solutions.
Spectrometer: An instrument that measures properties of light as a function of wavelength, frequency, or another variable. Spectrophotometers are a specialized kind of spectrometer focused on light interacting with samples.
Photodetector: A device that converts incident light into an electrical signal. It converts transmitted light into the signal used to calculate absorbance.
Optical path length: The distance light travels through an absorbing sample. It affects absorbance and must be known when estimating concentration.

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