What is beam direction?
The direction in which an airfield light aims its main beam. It decides which pilot sees the light, and what colour they see.
Every AGL fixture is built to be seen by a particular observer. Beam direction is where the fixture points its main beam, measured in azimuth relative to the runway or taxiway axis. Because colour is part of the message, direction matters as much as brightness: the same row of lights can read green to a pilot on approach and red to a pilot on the runway.
Fixtures fall into three families. A unidirectional fixture sends one beam one way, such as touchdown zone lights facing the approach, or a stop bar showing red toward the aircraft approaching the holding position. A bidirectional fixture sends two beams back to back, 180° apart along the runway axis, as runway centreline and edge lights do. An omnidirectional fixture shows light at all azimuth angles and is typical of taxiway edge lights rather than runway lighting.
A fixture that is rotated or misaligned at installation does not fail visibly in the daytime, but at night it shows its beam, and possibly the wrong colour, to the wrong observer. This is why orientation is verified during installation and commissioning.
Frequently Asked Questions
Q1What is beam direction in airfield ground lighting?
The direction in which a light fixture aims its main beam, measured in azimuth relative to the runway or taxiway axis. It determines which observer sees the light, and in what colour.
Q2What is the difference between unidirectional, bidirectional and omnidirectional fixtures?
A unidirectional fixture sends one beam in one direction. A bidirectional fixture sends two beams back to back, 180 degrees apart, along the runway axis. An omnidirectional fixture shows light at all angles in azimuth.
Q3Which runway lights face only one direction?
Touchdown zone lights face the approaching aircraft, stop bars show red toward aircraft approaching the holding position, and runway guard lights show yellow toward aircraft approaching the holding position. Threshold lights show green toward the approach, and at a runway extremity a back-to-back fixture shows red the other way as runway end lights.
Q4What happens if a fixture is installed facing the wrong way?
The light, and its colour, is shown to the wrong observer or at reduced intensity. For example, a colour-split threshold/end fixture rotated 180 degrees would show red to an approaching pilot and green toward the runway. This is why orientation is checked during installation and commissioning.
Q5Where are the aiming and alignment requirements defined?
In the applicable standard (ICAO Annex 14 and the Aerodrome Design Manual Part 4, or FAA AC 150/5340-30 for FAA-regulated airports) together with the fixture manufacturer's photometric and installation data. Always confirm against the current edition.
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