heat lightning

noun

1. lightning too distant for thunder to be heard, observed as diffuse flashes near the horizon on summer evenings.

noun

1. flashes of light seen near the horizon, esp on hot evenings: reflections of more distant lightning

1. Intermittent flashes of reddish or orange light near the horizon, usually seen on a hot summer evening and unaccompanied by thunder. Heat lightning is thought to be the reflection of distant lightning on clouds. Its color is believed to be due to the refraction of light in the atmosphere. See also sheet lightning. See more at lightning.