linguistic:translation, structural:reformatting
Counter-illumination

Counter-illumination means producing light to match a background that is brighter than an animal's body or military vehicle; it is a form of active camouflage. It is notably used by some species of squid, such as the firefly squid and the midwater squid. The latter has light-producing organs (photophores) scattered all over its underside; these create a sparkling glow that prevents the animal from appearing as a dark shape when seen from below. Counterillumination camouflage is the likely function of the bioluminescence of many marine organisms, though light is also produced to attract or to detect prey and for signalling.

Counterillumination has rarely been used for military purposes. " Diffused lighting camouflage " was trialled by Canada's National Research Council during the Second World War. It involved projecting light on to the sides of ships to match the faint glow of the night sky, requiring awkward external platforms to support the lamps. The Canadian concept was refined in the American Yehudi lights project, and trialled in aircraft including B-24 Liberators and naval Avengers. The planes were fitted with forward-pointing lamps automatically adjusted to match the brightness of the night sky. This enabled them to approach much closer to a target – within 3,000 yards (2,700 m) – before being seen. Counterillumination was made obsolete by radar, and neither diffused lighting camouflage nor Yehudi lights entered active service.