Runway Edge Light

A Runway Edge Light is a visual navigation aid that defines the lateral boundaries of the runway. Installed in pairs along the full length of the runway, these lights provide pilots with a clear outline of the runway's edges during takeoff, landing, and roll-out. The lights are typically white, but on precision approach runways (CAT II/III), the last 600 metres (or 2,000 feet) of runway edge lights are amber/yellow to indicate the final section. Intensity is variable to match prevailing visibility conditions.

The primary purpose of the runway edge light is to give pilots continuous, unambiguous reference to the lateral extremities of the runway during night operations and periods of reduced visibility, supporting safe alignment, directional control, and speed judgement throughout takeoff roll, final approach, landing, and rollout. Beyond simple edge delineation, the fixture also communicates positional context along the runway: the colour transition from white to yellow in the final 600 m / 2,000 ft on CAT II/III precision runways warns the pilot that the remaining runway length is limited, while the selectable intensity steps allow the light output to be matched to prevailing visibility so the edge remains visible without causing glare in clear conditions. In this way, the fixture serves both a delineation function (marking the usable runway width) and a situational-awareness function (signalling remaining distance and adapting to conditions).

Installed on both sides of the runway, spaced at uniform intervals (typically 60 m / 200 ft for precision runways, up to 100 m / 300 ft for non-precision). Used on all civil and military airfields that support night or low-visibility operations. Elevated fixtures are common on soft shoulders, while inset (flush) fixtures are used on hard surfaces or where aircraft overrun protection is required.

Fixtures are set out along both runway edges at the design spacing, positioned no more than 3 m outward from the pavement edge and clear of the graded runway strip's load-bearing requirements. Elevated units mount on a frangible coupling atop an L-867 base can set flush with grade, with the fitting height kept within the obstacle-limitation surface for the runway category. Inset units seat into an L-868 base can recessed into the pavement or shoulder, sealed against surface water ingress. Each base can is fed by armoured cable run in a trench (or duct) back to the isolating transformer pit, with the transformer housed in its own secondary base can adjacent to or below the fixture to keep the series-circuit joint out of standing water. Setting-out is tied to the runway centreline survey so the edge line remains parallel and true along the full runway length, and elevated fixtures are typically omitted or replaced with inset units within the runway end safety area and other frangibility-sensitive zones.

Each runway edge light is powered from the constant current series circuit via its own isolating transformer. The light's intensity is controlled by the CCR stepping current (typically 5 steps: 2.8A, 3.4A, 4.1A, 5.2A, 6.6A). The fixture uses either a halogen lamp or an LED array with a precision optical system to project the required beam pattern: a symmetric or asymmetric beam to ensure the light is visible to pilots on approach or during rollout. Elevated lights have a frangible coupling to break away on impact, minimizing aircraft damage.

Runway edge lights are not individually addressable — control is exercised at the loop level through the constant current series circuit. 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 therefore burns at the same intensity simultaneously — there is no way to dim or brighten a single fixture independently of the rest of the circuit. Fault detection is likewise loop-based: the CCR continuously monitors loop voltage against the commanded current, and a voltage rise at constant current signals increased circuit impedance, typically an open-circuit lamp or a failed isolating transformer, which is reported to the ALCMS as a loop fault rather than pinpointed to an exact fixture without further sectionalised testing.

The fixture body is typically a die-cast aluminium alloy housing, machined and anodised or powder-coated for corrosion resistance against runway de-icing fluids, fuel spillage, and UV exposure. The optical assembly sits under a borosilicate glass or high-strength polycarbonate prism, gasket-sealed to the housing with an O-ring or silicone seal to achieve an IP67/IP68 rating against water and dust ingress. Elevated units bolt to a frangible coupling, an aluminium or composite fitting engineered to shear cleanly under aircraft impact loads, which in turn seats on an L-867 base can set flush with the surrounding grade; inset (flush) units instead seat directly into an L-868 base can recessed into the pavement, with the top surface load-rated for aircraft wheel loading. Internal wiring terminates at L-823 primary connectors, sealed splice connectors rated for direct burial and continuous immersion, which mate to the secondary leads of the isolating transformer housed in its own base can nearby. Stainless-steel fasteners are used throughout to resist corrosion, and the base can assembly includes a drainage provision to prevent water pooling around the transformer and cable entry points.