Yehudi lights Yehudi lights are lamp s placed on the underside or wing leading edge 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 intended to disguise 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 , based on earlier research by the Canadian Navy in its " diffused lighting camouflage " project . It did not come into operational usage and was considered obsolete with postwar advances in radar . With more recent improvements in stealth technology , Yehudi lights have again attracted interest . US Navy research project . The use of Yehudi lights to camouflage aircraft by matching their luminance with the background sky was developed , in part , by the US Navy ' s Project Yehudi from 1943 onwards , following pioneering experiments in the Canadian " diffused lighting camouflage " project for ships early in the Second World War . The ships were fitted with ordinary projectors mounted on small platforms fixed to their sides , with the projectors pointing inwards at the ship ' s side . The brightness was adjusted to match the brightness of the sky . The Canadian experiment showed that such counter - illumination camouflage was possible , but the equipment was cumbersome and fragile , and the Canadian Navy did not take it further , despite interest from their allies . The key technology investigated under Yehudi was the fitting of lights to the undersides or fronts of antisubmarine and attack aircraft , since submarines at the surface could see the dark shape of an attacking aircraft against the night sky , and dive to safety . British researchers found that the amount of electrical power required to camouflage an aircraft ' s underside in daylight was prohibitive ; and externally mounted light projectors ( following the Canadian approach ) unacceptably disturbed the aircraft ' s aerodynamics . The American approach therefore used lamps mounted in the aircraft ' s nose and the leading edges of the wings . It was trialled in B - 24 Liberators , Avenger torpedo bombers and a Navy glide bomb from 1943 to 1945 . By directing the light forwards towards an observer ( rather than towards the aircraft ' s skin ) , the system provided effective counterillumination camouflage , more like that of marine animals such as the sparkling enope squid than the Canadian diffused lighting approach . However , the system never entered active service . Results . In 1945 a Grumman Avenger with Yehudi lights got within of a ship before being sighted , when under the same conditions an uncamouflaged plane was detected at a range of about 12 miles . It was noted at the time that this would force the enemy either to give up radar silence , making submarines easy to locate but harder to approach , or for observers to use binoculars continually . Since 8x binoculars at the time had a field of view of only 5 degrees , whereas enemy submarine s at the surface kept watch with three observers each assigned a 120 degree arc , the camouflage was considered effective . The ability to approach a target unseen was rendered obsolete by advances in radar in the 1940s and 1950s . Since the development of stealth technology , Yehudi lights have attracted renewed interest .