Corrupting Light

The Corrupting Light was a weapon utilized by the Great Diamond Authority as a means of corrupting the remaining Gems on Earth near the end of the Rebellion. The attack was a way to prevent the Crystal Gems from interfering with Homeworld agenda any further after the Earth colony failed and the planet was chosen to be used as an incubator instead. This light was first shown in "Same Old World" and later explained in "Monster Reunion". The light is composed of blue, white, and yellow rays, potentially referencing the diamonds of the same color.

History
In "Same Old World", Lapis states that there was a panic on Earth to escape after all hope of stopping the Rebellion was lost. After the majority of Homeworld Gems fled, a light was emitted from the sky. Later, in "Monster Reunion", the purpose of the light was explained by Centipeetle as a tool for corruption, most likely to ensure the rebellion could never threaten Homeworld, as well as an indirect way to destroy all life on the planet by way of the out-of-control monsters. Based on her recollection of the event, it is most likely that the majority of Gems were not aware of what exactly they were fleeing from.

Trivia

 * Steven interpreted Centipeetle's description as: "A sound? A song?".
 * In "Earthlings" it's revealed that the corruption can be spread through fusion.
 * The following gems were on Earth during the attack, but were not corrupted for various reasons:
 * Rose Quartz, Garnet, and Pearl (protected by Rose's shield)
 * Amethyst (presumably because she was still incubating in the Kindergarten)
 * Lapis Lazuli (unknown reasons, possibly related to being trapped in the mirror)
 * Bismuth (due to being bubbled)