NewsCovering Colorado


What are light pillars and why do they occur?

Carrie Zumwalt La Junta Light Pillars
Posted at 12:11 PM, Feb 04, 2022

Light pillars are optical atmospheric phenomena where pillars of light appear to beam up from the ground into the sky.

Amber Allen Canon City light pillars
Canon City, CO light pillars

The ideal weather conditions for this to occur are on a frigid winter night (often subzero temperatures) with high humidity and little to no wind.

Light pillars in Pueblo, CO. Courtesy NWS Pueblo

Under these conditions, tiny (about 0.02 mm) ice crystals will form and remain suspended in the atmosphere near the surface. The suspended ice crystals are great reflectors, beaming city lights back down to your eyes/camera lens.

Usually, these are plate-shaped ice crystals, which form at temperatures of 14° to -40° Fahrenheit or -10° to -40° Celsius.

Light pillars can occur without visible clouds in the sky since the ice crystals are so small. But, if low-level clouds are present at these frigid temperatures, they will consist of ice crystals and supercooled liquid droplets. These "icy" clouds typically occur at higher levels of the atmosphere, like cirrus clouds.

Low-level ice-filled clouds can also reflect city lights, creating a glow at a night. Pair the low clouds with a fresh blanket of snow, city lights are reflected even more. "Snowglow" can be twice as bright as a full moon, according to a 2019 study.

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