What causes sheet lightning as opposed to fork lightning?
Lightning is the result of a massive discharge of energy within clouds or between a cloud and the ground. When this discharge (or giant spark) occurs between the cloud and the ground, we refer to this as cloud-to-ground lightning. Some people call this fork lightning when the lightning channel has multiple points of contact to the ground. When a lightning discharge occurs within a cloud, the light is reflected off the water droplets within a cloud causing a diffusion of the light. At night, this diffusion of light from the original lightning channel causes the whole cloud or much of the sky to light up, creating the effect of a sheet of lightning.
