Aviation light signals

In the case of a radio failure or aircraft not equipped with a radio, or in the case of a deaf pilot, air traffic control may use a signal lamp (called a "signal light gun" or "light gun" by the FAA[1][2]) to direct the aircraft.

ICAO regulations require air traffic control towers to possess such signal lamps.

[3][4] The signal lamp has a focused bright beam and is capable of emitting three different colors: red, white and green.

[5][2][7] Planes can acknowledge the instruction by rocking their wings, moving the ailerons if on the ground, or by flashing their landing or navigation lights during hours of darkness.

[6][7] Air traffic control signal light guns are typically specified with a (white) center beam brightness of > 180,000 - 200,000 candela,[1][8][9] and are visible for roughly 4 miles in clear daylight conditions.