"A diffraction grating and a camera is all it takes to see what light is made of.
"KaiRenner26th of April 2026
How a Simple Spectrometer Works
A spectrometer splits light into its component wavelengths using a diffraction grating — a surface with microscopic parallel lines that diffracts different wavelengths at different angles. A CD or DVD cut into a strip works as a grating. Light enters through a narrow slit, diffracts off the grating, and projects a rainbow spectrum onto a detector (a webcam or camera sensor). Free software (Spectral Workbench) calibrates and reads the spectrum.
400to 700 nm
0.1to 1 nm
Build the Enclosure and Slit
Cut a narrow slit in a cardboard box — 0.5mm is the target width.
Build the Enclosure and Slit
Cut a narrow, straight slit in one end of a light-tight cardboard box using a razor blade and metal ruler. Target 0.5mm width — wider means lower spectral resolution, narrower means less light. Line the interior with matte black paper or paint to prevent internal reflections. Mount the box on a stable surface with the slit pointing toward your light source.
Cut and Mount the DVD Grating
Cut a strip from a DVD, remove the reflective layer, and mount at an angle.
Cut and Mount the DVD Grating
Cut a 2cm strip from a standard (not Blu-ray) DVD. Remove the reflective aluminum layer by peeling it away from the transparent polycarbonate — this leaves a clear grating. Mount the clear grating strip at the opposite end of the box from the slit, angled at approximately 45 degrees. The webcam looks through or alongside the grating.
Mount the Webcam and Capture Spectra
Point the webcam at the grating and capture the diffracted spectrum.
Mount the Webcam and Capture Spectra
Mount a webcam looking through the end of the box at the grating. The diffracted spectrum will appear as a rainbow stripe in the camera image. Use Spectral Workbench (spectralworkbench.org) or RSpec software for calibration and analysis. Calibrate using a known light source — a compact fluorescent lamp has sharp emission lines at known wavelengths.
What You Need
Old DVD (not Blu-ray)
Cardboard box — shoeboxes work well
Webcam or USB camera
Razor blade and metal ruler for the slit
Matte black paint or paper for interior
Spectral Workbench (free, web-based)
Calibration Makes the Difference An uncalibrated spectrometer shows a rainbow but cannot tell you wavelengths. Calibrate by capturing a compact fluorescent (CFL) bulb spectrum — CFLs have sharp mercury emission lines at precisely known wavelengths (435.8nm, 546.1nm, 611.6nm). Set these peaks in your software and the wavelength scale calibrates automatically across the visible range.
"The same tool, scaled up, tells us what distant stars are made of. Your version works on the same principle.
"KaiRenner26th of April 2026