Slow Light

Normally, light moves so fast that it seemingly instantly jumps from point A to point B, or at least faster than the eye can follow. Not when this trope comes into action. In this case, you can see light bounce all over the place instead of instantly seeing the new setup.

When applied to beam/laser weapons, may overlap with Painfully-Slow Projectile and/or Frickin' Laser Beams, depending on just how slow the light goes.

Sometimes done for effect in Bullet Time, or to establish causality for the viewer's convenience. Can be used to show off a Light and Mirrors Puzzle

Film

 * At the conclusion of Legend, the sunlight takes 20 seconds to reflect off all of the shields and reach the underground chamber where it blows away Darkness. Watch it here.

Literature

 * Light actually works this way in-universe in the Discworld. It's explained that this is because of the Disc's strong magical field distorting the way physical law works, slowing down light to roughly the speed of sound. In an extreme case, we find out that the Disc's sun actually travels at twice the speed of its own light ("this does not appear to cause any problems". Indeed, we find that an observer will start seeing a relativistic red/blue frequency shift while travelling in a magically enhanced coach at the unprecedented speed of 40 miles an hour.

Live Action TV

 * Bones: when Zack shows Booth & Brennan a mirror setup that the Gormagon used to watch the vault, he set off a laser beam that worked its way very slowly around the room.

Tabletop RPG

 * Dungeons & Dragons module T1-4 The Temple of Elemental Evil. When the PCs confront Zuggtmoy in her lair she activates a Prismatic Spray-type device that causes beams of light to spring forth and visibly bounce off things.

Western Animation

 * In one Scooby Doo episode, the gang gets locked in an ancient temple. To get out, they need to reflect moonlight onto a symbol on the wall a la Light and Mirrors Puzzle. However, instead of the light instantly appearing on the wall, we see a ray of light slowly bouncing between the mirrors until it reaches the wall. Worse yet, it misses at first, forcing Scooby to readjust just in time for another pulse of light to slowly move in and be reflected.
 * Acknowledged in the epilogue of one episode of Magic School Bus involving a light-based pinball-like game.