Valokehät

Valokehät is a Finnish term referring to luminous rings or halos observed around light sources, particularly streetlights, during foggy or misty conditions. These optical phenomena are created by the scattering of light as it passes through water droplets suspended in the air. The size and intensity of the valokehät depend on factors such as the size of the water droplets, the density of the fog, and the brightness of the light source.

The phenomenon is essentially a form of diffraction and refraction. Light waves from the source are bent and scattered by the tiny water droplets, which act as miniature lenses and prisms. This scattering causes the light to spread out, forming a visible ring or halo around the source. Different sizes of droplets can scatter light at slightly different angles, potentially contributing to the color variations sometimes observed within the rings, though they are often perceived as white or slightly yellowish.

Valokehät are a common sight in Finland and other Nordic countries during autumn and winter months when fog and mist are prevalent. While they are a natural atmospheric optical effect, their appearance can sometimes be perceived as beautiful or even slightly eerie, depending on the surrounding environment. They are not indicative of any atmospheric pollution or hazardous conditions, but rather a simple interplay of light and water vapor.