Tyndall effect

The Tyndall effect is when light is scattered by particles of matter in its path. It makes a beam of light visible by lighting the particles. It can be seen a suspension, or a mix of fluid and particles big enough to see, which settle down eventually.^[1]

Under the Tyndall effect, the longer-wavelength light is more transmitted while the shorter-wavelength light is more reflected by scattering. In effect, blue light is scattered much more strongly than red light because blue light has a shorter wavelength than red light.^[2]

The blue of a clear sky, and the blue of blue eyes is caused by the Tyndall effect, not by a pigment. Its named after John Tyndall. The effect can also be observed when sunlight passes through the canopy of a dense forest. It happens due to the scattering of light by the particles of smoke and dust. Another example is being able to see the beam of a projector in a movie theater when the lights are dim.^[3]

Before discovering the Tyndall Effect, John Tyndall worked on the absorption and release of heat with particles as small as molecules. In one of his experiments in the 1860s, he set up a glass tube and shone a white light through one end. Then, visible smoke was gradually added into the tube. He noticed that the light looked blue from the side of the tube but looked red from the far side. This was because the blue light scattered off of particles more easily because of its short wavelength. He thought the same thing happened in the sky, which is why it looks blue during daytime and red at sunrise and sunset, because at those times, the light passes through more atmosphere because of the sun's angle.^[4]

Later, in 1902, two scientists Richard Adolf Zsigmondy and Henry Siedentopf invented the ultramicroscope, a new microscope that could show very small objects by scattering light instead of reflecting or absorbing it. Using the Tyndall Effect, they were able to see a gold particle only 4 nm wide. Zsigmondy earned a Nobel Prize in Chemistry for this work.^[5][6]

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1. ↑ "15.10: Suspensions". Chemistry LibreTexts. 2016-06-27. Retrieved 2026-03-20.
2. ↑ "Tyndall Effect". Chemistry LibreTexts. 2013-10-02. Retrieved 2026-03-20.
3. ↑ "Tyndall_Effect". www1.chem.umn.edu. Retrieved 2026-03-20.
4. ↑ "John Tyndall's blue sky apparatus | Royal Institution". www.rigb.org. Retrieved 2026-03-20.
5. ↑ Mappes, Timo; Jahr, Norbert; Csaki, Andrea; Vogler, Nadine; Popp, Jürgen; Fritzsche, Wolfgang (2012-10-12). "The Invention of Immersion Ultramicroscopy in 1912—The Birth of Nanotechnology?". Angewandte Chemie International Edition. 51 (45): 11208–11212. Bibcode:2012ACIE...5111208M. doi:10.1002/anie.201204688. ISSN 1433-7851. PMID 23065955.
6. ↑ "Nobel Prize in Chemistry 1925". NobelPrize.org. Retrieved 2026-03-20.