Counter-illumination

Counter-illumination is a method of camouflage in which an animal (or possibly a military vehicle) produces light to match an illuminated background, such as the ocean surface or sky. It differs from countershading which uses only pigment, such as a vehicle's paint or the melanin in an animal's skin, to paint out the appearance of shadows. By adding the right amount of light through bioluminescence or electronically controlled lamps, counter-illumination can at best exactly match the brightness of the background, making for more effective camouflage than countershading can provide. Since counter-illumination allows the intensity of the generated light to be adjusted, camouflage can be actively adapted to varying lighting conditions and backgrounds.

Counter-illumination is one of the dominant methods of camouflage in marine organisms, along with transparency and silvering. All three methods make animals in open water resemble their environment.

Principle

Among marine organisms, counter-illumination camouflage occurs where bioluminescent light from an organism's ventral surface is matched to the light radiating from the environment. The bioluminescence is used to obscure the organism's silhouette produced by the down-welling light. Some midwater cephalopods, decapod crustaceans, and fishes utilize this form of camouflage.