Parts of a Spectrophotometer – Labeled Light Path Diagram

All 11 parts on the diagram

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The light path 8

Lamp (light source) It makes the white light.
Monochromator It turns white light into light of one narrow band.
Cuvette The clear container that holds the sample in the beam.
Detector It turns the light that reaches it into an electrical signal.
Lens It gathers the lamp's light onto the entrance slit.
Entrance slit White light enters the monochromator through it.
Diffraction grating It spreads white light into a spectrum.
Exit slit It lets one narrow band of the spectrum out.

The instrument 3

Display (meter) It shows how much light the sample let through.
Wavelength control Turning it moves the grating to pick the wavelength.
Sample compartment The cuvette sits in here, in the path of the light.

How this list was compiled: Every name checked on 2026-09-30 and kept only where at least two of these use it. (1) The Spectrophotometer: A Module on the Spectral Properties of Light, Physics of Technology series (a US college physics module; Tinker and McWane, Technical Education Research Centers), full text at https://archive.org/details/TheSpectrophotometer : source, lens, entrance slit, monochromator, diffraction grating, prism, exit slit, sample holder, detector, amplifier, meter. (2) Wikipedia, Spectrophotometry, https://en.wikipedia.org/wiki/Spectrophotometry : light source, monochromator, diffraction grating, slit, cuvette, detector. (3) Indian Standard IS 10679:1983, Photoelectric spectrophotometer (single beam type), full text at https://archive.org/details/gov.in.is.10679.1983 : lamp, monochromator, prism or grating, exit slit, sample holder, cuvettes, detector, display unit. (4) and (5) two makers' operating manuals, names only, full texts at https://archive.org/details/manualsplus_00092 with https://archive.org/details/manualzilla-id-6022835 (one instrument line: lamp, entrance slit, lenses, diffraction grating, exit slit, cuvette or test tube, sample compartment, phototube, meter, wavelength control) and https://archive.org/details/TurnerSP830Manual (lamp, entrance slit, monochromator, grating, exit slit, sample compartment, cuvettes, detector, display, wavelength dial). Licence: own work

The drawing: Own drawing from plain geometry; nothing traced. Licence: own work

How it works

A spectrophotometer measures how much light a sample lets through. Two drawings: the path of the light from the lamp to the detector, then a benchtop instrument with its display, wavelength control and sample compartment.

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The path of the light

The lamp makes white light, and the lens gathers it onto the entrance slit. Inside the monochromator the diffraction grating spreads the light into a spectrum. The exit slit lets one narrow band out. That band passes through the cuvette and reaches the detector.

From light to a reading

The detector turns the light that reaches it into an electrical signal, and the display shows it. Turning the wavelength control moves the grating, so a different part of the spectrum lines up with the exit slit.

A cuvette can be a small square tube, as drawn here, or a round test tube.

Questions and answers

What are the main parts of a spectrophotometer?

A lamp for the light, a monochromator with an entrance slit, a diffraction grating and an exit slit, a sample compartment that holds the cuvette, a detector, and a display.

What does the monochromator do in a spectrophotometer?

It turns white light into light of one narrow band. Its grating, or in some instruments a prism, spreads the light into a spectrum, and the exit slit lets only the chosen part through to the sample.

What is a cuvette?

A cuvette is the small clear container that holds the liquid sample in the beam. The light goes in one side and out the other on its way to the detector.

What does the detector do in a spectrophotometer?

It catches the light that comes through the sample and turns it into an electrical signal, which the instrument measures and shows on the display.