Mirrors, reflections, scattering:
At left twigs and branches act as mirrors. Those happening to be roughly perpendicular to the sun reflect its light towards the eye. Our brain – forever seeking patterns – merges the individual glints into circles, ‘light rings’. The branches were dry but even so reflected light well at glancing angles. Wet branches form even brighter rings.
Light is only reflected from mirrors - large surfaces smooth and continuous compared to the wavelengths of light. Rough surfaces scatter light.
Individual droplets in mist or clouds also scatter light. At upper right the scattering forms a corona. Each individual droplet scatters waves to form a circular diffraction pattern. Our eye sees a fragment of the pattern made by each drop and reassembles a whole – a corona of central white aureole and coloured rings.
Below: Both effects can be mathematically simulated.
||Simple geometry suffices to reproduce the reflections of light rings.
The diffraction of a corona requires lengthy mind numbing arithmetic only possible with modern computers that relish that sort of thing.