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Strobe lights are flashing white lights on the furthest left, right and, on larger aircraft and some smaller ones, back points of an aircraft. They are the brightest lights on the aircraft, and are used to signal that an aircraft is entering or approaching an active runway, or for visibility in dark, clear sky.
Red lights are commonly found to be used in urban areas, since it is easier for pilots to spot them from above. White strobes (that flash round the clock) (60 per minute for flashing marking "a unique signal that pilots should interpret as a warning that catenary wires are in the vicinity of the lights") may also be used in urban areas.
Typically, bulbs of 21 to 27 watts producing 280 to 570 lumens (22 to 45 mean spherical candlepower) are used for stop, turn, reversing and rear fog lights, while bulbs of 4 to 10 W, producing 40 to 130 lm (3 to 10 mscp) are used for tail lights, parking lights, side marker lights and side turn signal repeaters.
Watercraft navigation lights must permit other vessels to determine the type and relative angle of a vessel, and thus decide if there is a danger of collision. In general, sailing vessels are required to carry a green light that shines from dead ahead to 2 points (22 + 1 ⁄ 2 °) abaft [note 1] the beam on the starboard side (the right side from the perspective of someone on board facing ...
An emergency light is a battery-backed lighting device that switches on automatically when a building ... they turn on automatically. Standards. IEC 60598-2-22 Ed ...
If the voltage is of the wrong polarity, the device is said to be reverse biased, very little current flows, and no light is emitted. LEDs can be operated with alternating current, but they will only light on the half of the AC cycle where the LED is forward-biased. This causes the LED to turn on and off at the frequency of the AC supply.
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An Ottoman heliograph crew using a Blinkgerät (left) Begbie signalling oil lamp, 1918. Signal lamps were pioneered by the Royal Navy in the late 19th century. They were the second generation of signalling in the Royal Navy, after the flag signals most famously used to spread Nelson's rallying-cry, "England expects that every man will do his duty", before the Battle of Trafalgar.