page_title: Yehudi lights
section_title: Active camouflage in animals
hierarchical_section_title: Yehudi lights / Active camouflage in animals
caption_attribution_description: English: Principle of the counterillumination camouflage of the firefly squid, Watasenia scintillans. When seen from below by a predator, the bioluminescence helps to match the squid's brightness and colour to the sea surface above.
context_page_description: Yehudi lights are lamps of automatically-controlled brightness placed on the front and leading edges of an aircraft to raise the aircraft's luminance to the average brightness of the sky, a form of active camouflage using counter-illumination. They were designed to camouflage the aircraft by preventing it from appearing as a dark object against the sky.
  The technology was developed by the US Navy from 1943 onwards, to enable a sea-search aircraft to approach a surfaced submarine to "within 30 seconds of flying time" before becoming visible to the submarine's crew. This in turn enabled the aircraft to engage the submarine with depth charges before it could dive, to counter the threat from German submarines to allied shipping. The concept was based on earlier research by the Royal Canadian Navy in its diffused lighting camouflage project.
  Yehudi lights did not come into operational usage and were considered obsolete with postwar advances in radar. With more recent improvements in stealth technology, Yehudi lights have again attracted interest.
context_section_description: An equivalent active camouflage strategy, known to zoologists as counter-illumination, is used by many marine organisms, including fish, shrimps, and cephalopods such as the midwater squid, Abralia veranyi. The underside is covered with small photophores, organs that produce light. The squid varies the intensity of the light according to the brightness of the sea surface far above, providing effective camouflage by painting out the animal's silhouette with light.
caption: Principle of counter-illumination camouflage in squid. When seen from below by a predator, the animal's light helps to match its brightness and colour to the sea surface.
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