What are Light Pillars ?

Columns of light apparently beaming directly upwards from unshielded  (and wastefully polluting) lights are sometimes visible during very cold weather. Plate-shaped ice crystals, normally only present in high clouds, float in the air close to the ground and their horizontal facets reflect light back downwards. The pillars are not physically over the lights or anywhere else in space for that  matter ~ like all halos they are purely the collected light beams from all the  millions of crystals which just happen to be reflecting light towards your eyes  or camera. Artificial light pillars can be much taller than their natural counterparts because  rays from the lights are not parallel and plate crystals with small tilts can still  reflect them downwards. The crystals producing the pillars are roughly halfway  between you and the lights. When ice crystals float in the air around you, pillars (and other halos) can even be seen around streetlights a few meters away.