Yehudi lights

Yehudi Lights fitted to engine cowling and leading edges of a Grumman TBM-3D Avenger
Keywords	Active camouflage Counter-illumination
Project type	Military research
Funding agency	US Navy
Objective	Make brightness of aircraft match their backgrounds
Duration	1943 – 1945

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 "within 30 seconds of flying time", 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.

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.

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. A Canadian professor, Edmund Godfrey Burr, had serendipitously stumbled upon the principle when he saw an aircraft coming in to land over snow suddenly vanish; he realized that the reflected light had increased its brightness just enough to match the background sky. 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, arousing interest in both Britain and America, but the equipment was cumbersome and fragile, and neither the Royal Canadian Navy nor their allies brought it into production.