Editing Optical communication (section)

=== Signal lamps ===
{{Main|Signal lamp|Aviation light signals}}
[[File:TC with light gun.JPG|thumb|left|An [[air traffic controller]] holding a signal light gun that can be used to direct aircraft experiencing a radio failure (2007).]]
Signal lamps (such as Aldis lamps), are visual signaling devices for optical communication (typically using Morse code). Modern signal lamps are a focused lamp which can produce a pulse of light. In large versions this pulse is achieved by opening and closing shutters mounted in front of the lamp, either via a manually operated pressure switch or, in later versions, automatically.

With hand held lamps, a [[Curved mirror#Concave mirrors|concave mirror]] is tilted by a trigger to focus the light into pulses. The lamps are usually equipped with some form of optical sight, and are most commonly deployed on naval vessels and also used in airport control towers with coded [[aviation light signals]].

[[Aviation light signals]] are used in the case of a [[NORDO|radio failure]], an [[aircraft]] not equipped with a radio, or in the case of a hearing-impaired pilot. [[Air traffic controller]]s have long used signal light guns to direct such aircraft. The light gun's lamp has a focused bright beam capable of emitting three different colors: red, white and green. These colors may be flashing or steady, and provide different instructions to aircraft in flight or on the ground (for example, "cleared to land" or "cleared for takeoff"). Pilots can acknowledge the instructions by wiggling their plane's wings, moving their [[aileron]]s if they are on the ground, or by flashing their [[Aircraft landing lights|landing]] or [[navigation light]]s during night time. Only 12 simple standardized instructions are directed at aircraft using signal light guns as the system is not utilized with Morse code.