Awards, Grants, and Contests

Michael Yang

Award: Top 100

School: albany high school
Teacher: valerie risk
Category: Contrived
Photo #19128

A Flame's Shadow

There are many fascinating ways in which a flame and its surrounding light interact to create unique shadows unlike any other. In this photo,  a LEGO figure holds a match,  and behind it,  the shadow of both the figure and the flame stretch across the wall. You might assume a flame wouldn't cast a shadow since it produces light,  but if you shine a brighter light towards it,  a shadow appears. The shadow of the flame depends on its density and changes as you move up the flame. Near the base,  the flame burns hotter and cleaner,  with enough oxygen for most of the fuel to fully combust. This leads to fewer particles that are present to block light. Higher up,  the flame cools and oxygen becomes limited,  leading to incomplete combustion. Tiny bits of unburned carbon (soot) begin to form and rise,  making the top of the flame denser and more capable of casting a shadow.

The most fascinating part lies just beyond the shadowed flame,  a faint glowing outline. This isn't a result of the flame's obstruction of light,  nor is it emitted light,  but rather the refraction of light caused by the air around it. As the flame burns,  it heats the surrounding air unevenly,  creating pockets of differing temperatures and air densities. These gradients bend and refract the light passing through,  similar to the shimmering heat waves you see above asphalt on a hot day. The result is a ghostly outline that traces the flame's shape.