What is the phenomenon that light passes through clouds?

The phenomenon that light passes through clouds is called Tindal phenomenon.

When a beam of light passes through the colloid, a bright "path" can be observed in the colloid from the direction perpendicular to the incident light, and the appearance of Tindal effect also means that light can be seen. Photography circle, also known as "Jesus light", usually appears in the early morning, sunset or when there are more clouds after the rain. There is fog or dust in the atmosphere, just as the sun shines on it, divided into strips, sometimes a large piece, which is particularly spectacular.

1869, British scientist Tindal discovered the Tindal phenomenon. Tindal phenomenon is formed by visible light (wavelength is 400~700nm) scattered by dispersed particles in colloid. It can be used to distinguish colloid from solution in the laboratory. When light strikes a particle, two things happen. First, when the diameter of particles is many times larger than the wavelength of incident light, light is reflected. Second, when the particle diameter is smaller than the wavelength of incident light, light is scattered, and the scattered light is called milky light.

Causes of Dindal phenomenon

In the process of light propagation, when light shines on particles, if the particles are many times larger than the wavelength of incident light, light reflection will occur; If the particles are smaller than the wavelength of the incident light, light scattering will occur. What is observed at this time is the light radiated by light waves around the particles, which is called scattered light or milky light. Tindal effect is a phenomenon of light scattering or milky light. Because the diameter of true solution particles is generally less than 1nm, colloidal particles are between solute particles and suspension particles in the solution, and their diameter ranges from 1 ~ 100nm.

It is less than the wavelength of visible light (400 nm ~ 700 nm), so when visible light passes through colloid, it will have obvious scattering effect. For real solution, although the molecules or ions are small, the intensity of scattered light decreases obviously with the decrease of the volume of scattered particles, so the scattering effect of real solution on light is very weak. In addition, the intensity of scattered light also increases with the increase of particle concentration in the dispersion system.

The above contents refer to Baidu Encyclopedia -Tindal effect.