Reduce risk of inducing spatial disorientation using physiologically compatible ground lighting.

Spatial disorientation that occurs while landing aircraft during night operations may result in accidents and fatalities which are often classified as secondary to "pilot error." It has now been determined that the use of "expedient" lights, which include flares, flashlights, automobile headlights, etc., can induce spatial disorientation in pilots. The element that contributes to induction of spatial disorientation is the "point source of light" provided by these lights. Impingement on the retina of concentrated photon emissions, as supplied by incandescent (filament) lamps, flares, etc., produces an "after image," such as occurs when one briefly looks into the sun. The "after image" is caused by the time lag required for reconstitution of the neurohumoral transmitter substances in the retinal rods and cones. Pilots who develop "after images" during the final stage of landing a helicopter at night are predisposed to experiencing spatial disorientation, leading to aircraft mishaps. In contrast to flares or incandescent light sources, cold cathode lamps lack a "point source" of light emission, do not create an "after image," and are ideal to use in night landing operations. Cold cathode lights operating in the range of 512 nm (blue-green) are thought to be the most physiologically efficient color to use for night landing operations. Light sources in this nanometer range provide maximum visibility and safety for the pilot during landing operations under all environmental conditions.