This type of lightning, popularly called “sheet lightning” because it lights up the sky with a sheet of light, occurs within the thundercloud (intra-cloud lightning) or from one cloud to another (cloud-to-cloud lightning or inter-cloud lightning). It typically creates a diffuse illumination without a distinct channel being seen. This type of lightning includes the so-called heat lightning, consisting of diffuse light flashed from distant thunderstorms seen at the horizon. Sometimes lightning discharges originating below or within the anvil can be seen to move horizontally for some distance, generating multiple tree-like branches. These are known as “anvil crawlers”.