Runway Exit Light

A Runway Exit Light is an inset or elevated light fixture positioned on the runway surface to mark the location of a taxiway exit, rapid exit taxiway, or runway turnoff point. These lights are typically arranged in a row or pattern across the runway, providing pilots with a clear visual indication of where to turn off during the landing roll. The lights are usually green (for the exit path) or yellow (for caution areas), and they may be uni‑directional or bidirectional depending on the exit configuration. Runway exit lights are a critical component of airfield surface movement guidance, helping to reduce runway occupancy time and improve safety by ensuring pilots can quickly and confidently locate exits, especially in low visibility (RVR conditions) and at unfamiliar airports.

The runway exit light's purpose is to let a pilot identify and commit to a taxiway exit while still decelerating on the runway, rather than needing to slow further or come to a stop while searching for the correct turnoff — a difference that translates directly into reduced runway occupancy time and, at busy airports, meaningfully higher runway capacity. Its colour coding does double duty in this role: green marks the exit path itself so a pilot can identify it unambiguously, while yellow flags caution areas that should not be mistaken for the intended exit, a distinction that matters most in the low-visibility conditions where a wrong turn or a missed exit has the greatest operational consequence.

Runway exit lights are installed at the intersection of the runway and a taxiway exit, typically at the beginning of the exit curve. They are used on both precision and non‑precision runways, with rapid exit taxiways (RETs) often having dedicated exit light configurations. The lights are placed at regular intervals along the exit path, starting from the runway centreline and extending into the taxiway. They are commonly found at airports with high traffic volumes, where efficient runway vacating is essential for capacity. The fixtures may be flush‑mounted (inset) in the pavement for high‑speed exits or elevated on frangible poles for lower‑speed exits. In some configurations, the exit lights are integrated with lead‑off lights to provide sequential guidance towards the exit.

Exit lights are set out starting at the runway centreline and running along the exit path into the taxiway, spaced at regular intervals so the row of lights traces the curve a departing aircraft will follow. High-speed rapid exit taxiways typically use inset (flush) fixtures set into the pavement, since the exit curve is taken at speed and an elevated fixture would be a strike risk, while lower-speed exits may use elevated fixtures on frangible poles where the surface and traffic pattern allow it. Each fixture is tied into the same centreline and taxiway survey used for the runway and exit geometry, so the light row lines up exactly with the paved curve, and cabling is run underground back to the nearest junction box or isolating transformer serving that section of the runway edge circuit.

Each runway exit light is powered from the series circuit via an isolating transformer, with intensity controlled by the CCR's current steps (typically 5‑step, 2.8A – 6.6A). The fixture uses a precision optical system (reflector and prism) to project a narrow beam towards the approaching aircraft, aligned along the runway centreline or angled towards the exit. The green colour indicates the exit path direction, while yellow may be used for caution areas or holding positions. Some exit lights are bidirectional, visible to pilots on both approach and departure, while others are uni‑directional, visible only from the approach side. Because all fixtures on a loop are switched and dimmed together by the CCR, the sense of direction is built into the row optically — through fixture aim, uni-/bi-directional lensing, and colour — rather than through any per-fixture electrical sequencing or flashing. The fixtures are designed to withstand heavy aircraft loads (up to 100,000 kg for inset versions) and harsh environmental conditions.

Runway exit lights are not individually addressable — control is exercised at the loop level through the constant current series circuit, typically the same runway edge circuit or a dedicated exit-lighting loop. An Airfield Lighting Control and Monitoring System (ALCMS), operated by the tower or an automated visibility-linked routine, selects the required brightness step based on prevailing RVR, ATC instruction, or (at smaller aerodromes) pilot-controlled lighting input. This command is passed to the CCR, which regulates the entire loop to the corresponding fixed current (one of 5 steps between 2.8A and 6.6A). Every fixture on that loop, via its own isolating transformer, draws from the same current and burns at the same intensity simultaneously — there is no way to dim, brighten, or sequence a single exit light independently of the rest of the loop, so directional or sequenced flash patterns are implemented optically (lens angle, reflector aim) rather than through per-fixture electrical commands. Fault detection is likewise loop-based: the CCR monitors loop voltage against the commanded current, and a voltage rise signals increased circuit impedance — typically an open-circuit lamp or a failed isolating transformer — reported to the ALCMS as a loop fault rather than pinpointed to an exact fixture without further sectionalised testing.

The fixture follows the same general construction as other runway inset or elevated lights: a die-cast aluminium housing, anodised or powder-coated for corrosion resistance, with the optical assembly — an LED array or halogen lamp behind a green or yellow filtered lens or prism — gasket-sealed with an O-ring to achieve an IP67/IP68 rating for surface-mounted, wheel-loaded installations. Inset units seat in an L-867/L-868-style base can recessed into the runway pavement with the top surface load-rated for aircraft wheel traffic, while elevated units mount on a frangible coupling designed to shear cleanly under impact, seated on a base can set into the surrounding grade. Because exit lights are frequently arranged as a directional row or curve marking the turnoff path, each fixture in the set is individually aimed during installation to project its beam along the intended taxi path. Internal wiring terminates at sealed L-823 primary connectors mating to the secondary leads of a nearby isolating transformer, with stainless-steel fasteners and a base can drainage provision completing the assembly.