Forms of Optical Communication
There are many forms of non-technological optical communication, including body language and sign language.
Techniques such as semaphore lines, ship flags, smoke signals, and beacon fires were the earliest form of technological optical communication.
The heliograph uses a mirror to reflect sunlight to a distant observer. By moving the mirror the distant observer sees flashes of light that can be used to send a prearranged signaling code. Navy ships often use a signal lamp to signal in Morse code in a similar way.
Distress flares are used by mariners in emergencies, while lighthouses and navigation lights are used to communicate navigation hazards.
Aircraft use the landing lights at airports to land safely, especially at night. Aircraft landing on an aircraft carrier use a similar system to land correctly on the carrier deck. The light systems communicate the correct position of the aircraft relative to the best landing glideslope. Also, many control towers still have an Aldis lamp to communicate with planes whose radio failed.
Free-space optical communication is also used today in a variety of applications.
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