Light passing through a colloid is scattered by suspended particles. The light beam becomes clearly visible; this phenomenon is called the Tyndall effect. For example, car headlight beams can be seen in fog, but the beams are invisible in clear air.
the scattering of light by the particles within a chamber. Baking soda and talc used to pack air bags can be inhaled by the suspect upon deployment and exhaled in to breath machines, deflecting the light beams in the machine and producing a higher blood-alcohol reading.
When a very dilute dispersion of small particles or droplets is viewed directly against an illuminating light source it may appear to be transparent. In contrast, when the same dispersion is viewed from the side (at a right angle to the illuminating beam), and against a dark background, the dispersion may appear turbid and blue-white in colour. The scattered light is due to Tyndall scattering and the optical effect is referred to as the Tyndall effect.
The term Tyndall effect is usually applied to the effect of light scattering on particles in colloid systems, such as suspensions or emulsions. It is named after the Irish scientist John Tyndall. The Tyndall effect is used to tell the difference between the different types of mixtures, namely solution, colloid, and suspension.