Yehudi lights are lamps placed on the underside or wing leading edge of an aircraft. Their purpose was to raise the aircraft's luminance to the average brightness of the sky. They were intended to disguise the aircraft by preventing it from appearing as a dark object against the sky. The technique, counter-illumination, is a form of active camouflage.
The use of the lights to match an aircraft's luminance with the background sky was developed, in part, by the the US Navy's Project Yehudi in the early 1940s, following pioneering experiments in the Canadian Diffused lighting camouflage project. One of the technologies investigated under Yehudi was the fitting of lights to the undersides or fronts of antisubmarine and attack aircraft.
In 1945 a Grumman Avenger with Yehudi lights got within 3,000 yards (2,700 m) of a ship before being sighted. This ability was rendered obsolete by the radar of the time. Since the development of stealth technology, Yehudi lights have come under renewed interest.
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