Road flare

A flare , also sometimes called a fusee, is a type of pyrotechnic that produces a brilliant light or intense heat without an explosion. Flares are used for signalling, illumination, or defensive countermeasures in civilian and military applications. Flares may be ground pyrotechnics, projectile pyrotechnics, or parachute-suspended to provide maximum illumination time over a large area. Projectile pyrotechnics may be dropped from aircraft, fired from rocket or artillery, or deployed by flare guns or handheld percussive tubes.

The earliest recorded use of gunpowder for signalling purposes was the 'signal bomb' used by the Song Dynasty Chinese as the Mongol-led Yuan Dynasty besieged Yangzhou in 1276. These soft-shelled bombs, timed to explode in mid-air, were used to send messages to a detachment of troops far in the distance. Another mention of the signal bomb appears in a text dating from 1293 requesting their collection from those still stored in Zhejiang. A signal gun appears in Korea by 1600. The Wu I Thu Phu Thung Chih or Illustrated Military Encyclopedia written in 1791 depicts a signal gun in an illustration.

Flares produce their light through the combustion of a pyrotechnic composition. The ingredients are varied, but often based on strontium nitrate, potassium nitrate, or potassium perchlorate and mixed with a fuel such as charcoal, sulfur, sawdust, aluminium, magnesium, or a suitable polymeric resin. Flares may be colored by the inclusion of pyrotechnic colorants. Calcium flares are used underwater to illuminate submerged objects.

...
Wikipedia