Tyndall Effect

Core Concepts – Tyndall Effect

In this tutorial, you will learn about the tyndall effect: what it is, why it happens, and how we define it. This concept is crucial in understanding the relationship between light and particles in solution.

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What is the Tyndall Effect?

The Tyndall effect is the phenomena in which light scatters as it passes through a colloidal mixture. Colloids’ unique solvent particle size range gives them the ability to allow some light to pass through the solution, while some is scattered outwards. Colloids have particles within the range 100-900 nm and therefore, many colloids have particles which are similar to the wavelengths of light passing through. While the mathematics regarding the Tyndall effect is beyond the scope of this article, the general trend demonstrates that larger wavelengths of light are often less scattered than shorter wavelengths of light.

An important distinction to make regarding the Tyndall effect is that no chemical or physical changes are undergone during the phenomena. Furthermore, this effect is used to determine whether a mixture is a pure solution or colloid. While a solution would have little scattering(or change in scattering intensity over time due to solvation), colloids would experience no change in scattering.

Image of light beams visible due to the Tyndall effect (From Lilydjwg on Wikimedia)

What is scattering?

Light scattering is the process by which light waves are dispersed after coming into contact with particles. Scattering impedes the path of light, and hence, individual photons are reflected outwards upon collision with small particles. Scattering is the process which contributes to the blue hue of the sky. As light travels from the sun to the Earth containing all wavelengths of light, blue light is scattered outwards more than other colors. Our eyes, while not looking at the sun, therefore perceive a blue sky. This is not necessarily Tyndall effect, but the example demonstrates the process of general scattering.

Different colors in the sky  due to scattering from the Tyndall effect
The blue light scattered by the particulate in the earth’s atmosphere

Comparison to Rayleigh Scattering

One common used comparison to Tyndall scattering is the phenomena of rayleigh scattering. Rayleigh scattering is undergone by particles which are significantly smaller than wavelengths of light(around one tenth the size). Usually these particles make solutions which are far more dissolved than a colloid and have solutes which are less visible by the naked eye. Hence, their scattering is far less intense, as less light is reflected from each particle. This particle size dependency is used to determine the size of unknown aerosol particles in a technique known as turbidimetry. Furthermore, this analytical method is used in biological, environmental, and inorganic applications, especially in recently popular advances in nanoparticle characterization technology.

Many mathematical techniques used to describe the Tyndall effect are derived from rayleigh scattering equations. Particles can be analyzed as spheres, spheroids or various other 3 dimensional shapes using a variety of mathematical techniques. These formulas can help predict the intensity and wavelength of light which is scattered given a particular particle.

Common Examples of Tyndall Effect

Laser through a solution and a colloid, displaying the Tyndall effect
The laser light scatters in the right beaker due to particles present, which is an illustration of the Tyndall effect.
  • A light shone through a solution of milk diluted heavily with water
  • Headlights shone through a foggy atmosphere creating a visible beam
  • A blue iris, which has particles that scatter blue light
  • Light scattering due to smoke
  • Visible blue exhaust fumes seen during the daytime from motorcycles or cars

Practice Problems

Problem 1

An aqueous mixture which has particle size of 2 mm experiences a large amount of scattering when a light is shined on it. Generally, would this mixture be considered a colloid?

Problem 2

True or False: The sky appears blue due to the reflection blue light off of the clouds in the atmosphere.


Problem 1

This mixture would not be considered a colloid because the particle size is not within 100-1000 nm in size. This is the defining characteristic which determines whether a solution is a colloid or not.

Problem 2

False. The particulate matter in the atmosphere causes scattering of light, which causes the sky to appear blue. However, clouds may only be a small portion of the many particles which contribute to this color difference. Additionally, it is not the reflection, but rather the scattering of light which causes the blue appearance.