Light pillars are optical phenomena that occur in extremely cold atmospheres, when flat ice crystals form close to the ground. They reflect natural and artificial light in columns that extend through the sky.
A light beam is a directional projection of light energy from a radiating source such as lamps, torches, etc., Whereas Light pillars are just an illusion created by the ice crystals reflecting the light.
Each horizontally positioned ice flake acts as a tiny mirror reflected the light that is underneath it and the presence of flakes at a spread of altitudes causes the reflection to be elongated vertically into a column.
Photo by Darlene Tanner in Alberta, Canada.