Cloud PointField Guide

Optical phenomenon — ice crystals

Light Pillars

Vertical beams above ground lights on frozen nights

Written by Laurence WayneEntry No. 49Uncommon

Light Pillars: Vertical beams above ground lights on frozen nights
Plate XLIXPhotograph by Raitisfreimanis, CC BY-SA 4.0.

A light pillar is a vertical shaft of light that appears to stand above a light source. It is created when flat, plate-shaped ice crystals drifting nearly horizontally through cold air act as tiny mirrors, reflecting light from below up towards the observer. Because crystals at many heights each add their reflection, the combined glints smear into a tall column. The source can be the sun or moon, or ground lights such as streetlamps.

Worth knowing

  • A light pillar is a pure optical illusion — no light actually travels up into the sky. The column is just the combined glints from countless mirror-like crystals lined up in your sightline, exactly the way a streetlight stretches into a shimmering line across rippled water.
Note

Still unsure it's the same cloud? Our app, Cloud Point— on iOS and Android — reads a photo and returns the likely type with altitude, useful when a formation is fading faster than you can look it up.

Test yourselfThree levels

Choose a difficulty

What conditions produce ground light pillars?

  1. aA hot, humid afternoon
  2. bA very cold night with ice crystals in the air
  3. cA foggy autumn morning
  4. dA windy spring storm
Show answer

AnswerA very cold night with ice crystals in the air

They need tiny ice crystals suspended in very cold, still air above a light source.

How do the ice crystals create the vertical column?

  1. aThey split light into a spectrum like a prism
  2. bThey act as tiny horizontal mirrors reflecting light up to your eye
  3. cThey glow with their own heat
  4. dThey bend light around corners
Show answer

AnswerThey act as tiny horizontal mirrors reflecting light up to your eye

Flat, near-horizontal plate crystals reflect the source light; crystals at many heights combine into a column.

Why does a light pillar always stand directly above (or below) its light source, never off to one side?

  1. aThe light source only shines straight up
  2. bOnly crystals in the vertical plane through your eye and the light reflect glints back to you, stacking into a vertical line
  3. cThe wind blows the crystals into a standing vertical wall
  4. dThe pillar lines up with the Earth's magnetic field
Show answer

AnswerOnly crystals in the vertical plane through your eye and the light reflect glints back to you, stacking into a vertical line

Each near-horizontal crystal acts as a mirror; only those lying in the vertical plane joining you and the light send a glint to your eye, so the reflections stack straight up into a column.

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