A substance must have one or more dimensions (length, breadth or thickness) in the approximate range of 1-1000 nm to be classified as a colloidal.

Light cannot pass straight through a colloidal solution or substance (like fog) because it is made of dispersed particles (like dust and water in air).

Instead, it collides with the micro-particles and scatters, producing the appearance of a visible light beam. The Tyndall effect was first noticed and reported by John Tyndall.

The Tyndall effect is a simple method for assessing whether or not a combination is colloidal.

When it so happens that a light is reflected through a real solution, it passes through very clearly. But when the light is reflected through a colloidal solution, the substance will scatter in phases and the light will be reflected in all directions, making it visible. Light shining through water and milk, for example.

Because it is not a colloid, light does not reflect when travelling through water.

When it passes through colloidal milk, it is reflected in all directions.

Another example is shining a flashlight into fog or smog; because the fog is a colloid, the beam of light is plainly visible.

Examples of Tyndall effect 

• The blue colour of the sky is due to the Tyndall effect.
• Because milk is a colloidal substance, light diffuses through it when a beam of light travels through it.
• Because fog is a colloidal substance, light collides with the particles as it reaches the molecules of air in a foggy environment, scattering and diffusing the light in many directions.
• Likewise, as light shines between numerous layers of cloud, it diffuses in different directions on the surface.
• The Tyndall phenomenon, which causes light to scatter in the stroma and reflect in blue, green or hazel hues, is to blame.
• Another example is, when the sun sets and the sky colour changes, this is due to the Tyndall effect, which is influenced by the sun’s position and the atmosphere as light passes through it.
• The Tyndall effect can be shown by shining a flashlight through a glass full of milk. To see the effect of the colloid particles on the light beam, you might wish to skim milk or even dilute it with water. 
• The blue smoke from motorcycles or two-stroke engines is an illustration of the way the Tyndall effect leads to scattering of blue light. 
• The Tyndall effect is responsible for a very prominent headlight beam in the midst of a fog. Light is scattered by water droplets, making the headlight beams clearly visible.
• The Tyndall effect is used to understand the size of the particles of aerosols in commercial and laboratory settings.
• The Tyndall effect is visible in opalescent glasses.

The sky’s blue colour is caused by light scattering, which is known as Rayleigh scattering, rather than by the Tyndall effect because the particles involved are air molecules.

Tyndall Effect: What Causes It?

An interaction with the spectrum of the light which becomes visible along with the constituent light particles of a colloidal solution and other tiny suspensions causes the Tyndall effect in colloidal solutions.

As a result, the closer or higher the contact between the light beams and the particles, the greater will be the scattering and the greater is the chance of observing a Tyndall effect.

The visible spectrum of light has a wavelength of 400 nm to 700 nm, with blue light having a wavelength of 400 nm to 500 nm and red light having a wavelength of 600 nm to 700 nm.

A colloidal solution is also known as a heterogeneous combination amidst which a constituent particle has a size of 1-1000nm, yet these particles are small compared with others as they will not be separated by filtration. However, centrifugation and several other ways can be used to get relative densities like those in milk.  

Conclusion

The Tyndall effect is also known as a distinguishing property of a solution that is colloidal and it can also be used to find out the difference between a real solution and a colloidal solution.