page_title: Counter-illumination
section_title: For aircraft
hierarchical_section_title: Counter-illumination / Military prototypes / For aircraft
caption_attribution_description: English: Principle of Yehudi lights counter-illumination camouflage. Silhouettes of oncoming Grumman Avenger against sky with and without lamps. The lamps were automatically adjusted to match the brightness of the sky, reducing the visibility of the plane as seen from a potential target (ship or surfaced submarine) by up to 70%.
context_page_description: Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength.
  Marine animals of the mesopelagic zone tend to appear dark against the bright water surface when seen from below. They can camouflage themselves, often from predators but also from their prey, by producing light with bioluminescent photophores on their downward-facing surfaces, reducing the contrast of their silhouettes against the background. The light may be produced by the animals themselves, or by symbiotic bacteria, often Aliivibrio fischeri. Counter-illumination differs from countershading, which uses only pigments such as melanin to reduce the appearance of shadows. It is one of the dominant types of aquatic camouflage, along with transparency and silvering. All three methods make animals in open water resemble their environment.
context_section_description: In 1916 the American artist Mary Taylor Brush experimented with camouflage on a Morane-Borel monoplane using light bulbs around the aircraft, and filed a 1917 patent that claimed she was "able to produce a machine which is practically invisible when in the air". The concept was not developed further during the First World War.
  The Canadian ship concept was trialled in American aircraft including B-24 Liberators and TBM Avengers in the Yehudi lights project, starting in 1943, using forward-pointing lamps automatically adjusted to match the brightness of the sky. The goal was to enable a radar-equipped, sea-search aircraft to approach a surfaced submarine to within 30 seconds from arrival before being seen, to enable the aircraft to drop its depth charges before the submarine could dive. There was insufficient electrical power available to illuminate the entire surface of the aircraft, and outboard lamps in the manner of diffused lighting camouflage would have interfered with the airflow over the aircraft's surface, so a system of forward-pointing lamps was chosen. These had a beam with a radius of 3 degrees, so pilots had to fly with the aircraft's nose pointed directly at the enemy. In a crosswind, this required a curving approach path, rather than a straight-line path with the nose pointed upwind. In trials in 1945, a counter-illuminated Avenger was not seen until 3,000 yards (2,700 m) from its target, compared to  12 miles (19 km) for an uncamouflaged aircraft.
  The idea was revisited in 1973 when an F-4 Phantom was fitted with camouflaging lights in the "Compass Ghost" project.
caption: Forward-pointing Yehudi lights on Grumman TBM Avenger raised the average brightness of the plane from a dark shape to the same as the sky.[b]
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