Runway Lighting
The visual reference system that defines the runway itself — edges, centreline, threshold, end, and touchdown zone — giving pilots continuous positional awareness through landing, roll-out and takeoff, day or night.
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What Is It?
Runway lighting is the set of fixed and, in some cases, sequenced light systems that mark the physical boundaries and key reference points of a runway. Unlike approach lighting, which guides an aircraft toward the runway, runway lighting defines the runway itself once the aircraft is over it or rolling along it — where the edges are, where the usable surface begins and ends, and where the touchdown zone lies.
Each runway lighting subsystem communicates something different through colour, position and, in some systems, flash pattern — together they let a pilot judge alignment, remaining distance and runway limits without relying solely on instruments.
Purpose & Function
Runway lighting's purpose is to let a pilot judge exactly where they are relative to the runway itself — its edges, its usable start and end points, the touchdown zone — at the specific phases of flight (final approach, landing, rollout) where that judgment can't be deferred to instruments alone. Each subsystem's colour and position exists to answer a different question at a glance: white edge lighting answers 'where are the boundaries', red end lighting answers 'how much runway is left', and touchdown zone lighting answers 'am I landing in the right place' — together giving the pilot the same spatial awareness in fog or at night that would otherwise only be available in clear daylight.
Where Is It Used?
Runway lighting subsystems are installed along and around the full length of the runway:
- Runway Edge Lights: Run the full length of the runway on both sides, typically white, marking the lateral limits of the usable surface.
- Runway Centreline Lights: Embedded along the runway centreline on precision-approach runways, aiding alignment in low visibility.
- Threshold Lights: Mark the beginning of the runway available for landing.
- Runway End Lights: Mark the far end of the runway, typically red when viewed from the runway.
- Touchdown Zone Lights: Installed in the initial portion of the runway to help pilots judge the touchdown point in low visibility.
- Runway Guard Lights: Positioned at runway-holding positions on the taxiway side, warning of the approach to an active runway.
The specific systems required at a given runway depend on its classification (e.g. non-instrument, non-precision approach, precision approach CAT I/II/III) under the applicable ICAO or FAA standard.
Installation & Location
Each subsystem is set out along the runway according to its own specified spacing and offset — edge lights at uniform intervals down both sides, centreline lights embedded along the surveyed centreline, threshold and end lights in a row at each end, and touchdown zone lights in the paired barrettes covering the initial landing zone — with the complete layout tied back to a single runway survey so every subsystem's geometry remains consistent relative to the others. Mounting method (elevated or inset) is chosen per subsystem and location, with inset fixtures used within the runway strip and touchdown zone where a protruding fixture would be a hazard, and elevated fixtures reserved for locations such as unpaved shoulders where flush mounting isn't practical. Runway guard lights, though positioned on the taxiway side of a holding point rather than on the runway itself, are set out and surveyed against the same runway reference so their warning function lines up correctly with the runway threshold they protect. Cabling for each subsystem generally runs on its own series circuit back to a dedicated regulator, so a fault in one subsystem — edge lighting, for example — doesn't take down an unrelated subsystem such as centreline or touchdown zone lighting.
How Does It Work?
Runway lighting fixtures are wired into AGL series circuits fed by one or more CCRs, with each fixture isolated from the shared primary loop by its own isolating transformer. Intensity across the whole circuit is controlled together by the CCR's selectable current steps, allowing the same runway edge circuit to run at low intensity on a clear night and high intensity in fog, without rewiring anything.
Key functional aspects include:
- Colour Coding: White for edge and most centreline lighting, red for the runway end, with colour changes near the far end of some centreline systems to warn of the remaining distance.
- Spacing and Configuration: Longitudinal and lateral spacing is defined by the applicable standard and runway classification — consistency of spacing is itself a visual cue to the pilot.
- Intensity Steps: Selectable brightness levels let the same fixtures serve clear-night and low-visibility operations.
- Elevated vs. Inset Fixtures: Elevated fixtures are used where FOD and jet blast risk is lower; inset (flush) fixtures are required on and near the runway surface itself.
System Architecture & Control Logic
Runway lighting is controlled at the circuit level, the same way an individual runway edge light loop is, but a runway typically runs several such circuits side by side — separate loops for edge lighting, centreline lighting, threshold lighting, and touchdown zone lighting, each fed by its own CCR. The ALCMS or tower selects an intensity step appropriate to prevailing RVR or ATC instruction, and that command is applied per circuit, so the whole runway lighting picture is really several loop-level control systems operating in parallel rather than one.
Keeping these subsystems on separate circuits means a fault on the touchdown zone lighting, for instance, is reported and can be worked on independently of the edge or centreline circuits — and it also means intensity can, on more advanced installations, be stepped differently between subsystems (touchdown zone and centreline lighting are sometimes run brighter than edge lighting) rather than being locked to a single runway-wide value.
ALCMS → CCR (per subsystem) → Series Circuit Loop → Isolating Transformer → Fixture (loop-level feedback)
Circuit & System Overview
Every runway lighting subsystem taps the same series loop through its own isolating transformer, but each carries a different colour, position and fixture type — and the CCR's current step raises or lowers all of them together, so visibility conditions are handled by dialling the circuit rather than swapping fixtures.
Physical Construction
Despite their differing colours and positions, the subsystems share a common build. Elevated fixtures (edge, threshold, end) use a die-cast aluminium housing, anodised or powder-coated for corrosion resistance, with the optical prism gasket-sealed under an O-ring or silicone seal and bolted to a frangible coupling that shears cleanly on impact before seating on an L-867 base can set flush with the surrounding grade. Inset fixtures (centreline, touchdown zone) dispense with the frangible coupling, instead seating directly in an L-868 base can recessed into the pavement with a load-rated top surface designed to take aircraft wheel loading. In both cases, internal wiring terminates at L-823-style connectors that mate to the secondary leads of an isolating transformer housed in its own nearby base can, with stainless-steel fasteners and a drainage provision keeping the enclosure watertight through years of runway service.
Technical Parameters
| Parameter | Typical Value |
|---|---|
| Typical Colour — Edge | White (with variations near the runway end depending on the standard) |
| Typical Colour — Threshold | Green |
| Typical Colour — Runway End | Red |
| Typical Colour — Centreline | White, changing near the runway end on some systems |
| Fixture Type | Elevated (edge/threshold) or inset/flush-mounted (centreline, touchdown zone) |
| Circuit Type | Series circuit fed by CCR, 6.6A standard loop current |
| Intensity Steps | Multiple selectable steps per applicable specification |
| Standards | ICAO Annex 14, FAA AC 150/5340 series, IS 7785 |
Electrical Requirements
| Requirement | Typical Value |
|---|---|
| Circuit Type | Series circuit, constant current (CCR fed); edge, threshold, centreline, and touchdown zone lighting typically on separate circuits |
| Rated Series Current | 6.6A (5-step: 2.8A / 3.4A / 4.1A / 5.2A / 6.6A), common across the runway lighting system |
| Isolation | Each fixture fed via its own isolating transformer (wattage varies by fixture type), off the shared series loop |
| Circuit Segregation | Separate CCRs/circuits per lighting category allow independent intensity control and isolate faults to a single system |
| Cable Type | L-824 single-conductor, direct-burial rated, 5kV or 600V per circuit design |
| Connector | L-823 primary connector, submersible-rated splice at every fixture |
| Insulation Resistance | ≥ 50 MΩ (megger test, cable-to-ground) |
| Earthing/Grounding | Fixture bodies, base cans, and duct/cable runs bonded to the airfield earth grid |
| Fault Protection | CCR-level ground fault and open-circuit detection per circuit |
| Power Source | CCR output per circuit, regulated per ICAO/FAA intensity step schedule |
Photometric Requirements
| Parameter | Typical Value |
|---|---|
| Main Beam Intensity — Edge | ≥ 10,000 cd (white), per ICAO Annex 14 / FAA AC 150/5340 series |
| Main Beam Intensity — Threshold/End | ≥ 8,000 cd (green threshold), ≥ 8,000 cd (red runway end) |
| Main Beam Intensity — Centreline | ≥ 6,500 cd (white), stepping down through red/white and red zones near the runway end |
| Vertical/Horizontal Beam Spread | Per fixture type — elevated edge/threshold lights and inset centreline/touchdown zone lights each follow their own Annex 14 figure |
| Isocandela Distribution | Per ICAO Annex 14 Attachment A / FAA AC 150/5340 series figures for each light type |
| Chromaticity | Within ICAO Annex 14 white, green, and red boundaries as applicable (CIE coordinates) |
| Intensity Steps | Multiple selectable steps, coordinated across edge, threshold, centreline, and touchdown zone circuits |
| Intensity Tolerance | ± 25% of rated value at each CCR step (field measurement) |
| Maintenance Factor | ≥ 50% of new-fixture intensity before lamp/lens replacement is due |
| Test Method | Mobile photometric van/goniophotometer or fixed test bench, per fixture type and circuit |
Applicable Standards
ICAO Annex 14
International standards for runway lighting configuration by runway classification
FAA AC 150/5340-24 / -30
U.S. specifications for runway edge, centreline and touchdown zone lighting
IS 7785
Indian Standard for airfield lighting equipment and installation practice
DGCA CAR Section 4
Indian regulatory requirements for aerodrome lighting
Installation Requirements
Base Can Excavation by Subsystem
CivilExcavate and set base cans to each subsystem's mount type — L-867 elevated for edge, threshold, and end lights; L-868 inset for centreline and touchdown zone lights — holding each flush with the surrounding grade or pavement.
Single-Survey Set-out
CivilSet out every subsystem (edge, centreline, threshold, end, touchdown zone, runway guard lights) from one runway survey, at each subsystem's own specified spacing and offset, so the complete layout stays geometrically consistent.
Drainage Provision
CivilProvide a weep hole or drainage path at each base can to prevent water pooling around the transformer and cable entry, particularly for inset fixtures.
Per-Subsystem Circuit Routing
ElectricalRoute each subsystem's series circuit duct back to its own dedicated regulator, keeping cabling separate so a fault in one subsystem cannot take down an unrelated one.
L-823 Connector Termination
ElectricalTerminate and seal the primary connector at every fixture per manufacturer procedure, keeping each splice submersible-rated before backfill.
Isolating Transformer Matching
ElectricalConfirm each isolating transformer's wattage matches its fixture and its subsystem circuit's rated current step before connection.
Mount-Type Fixing by Subsystem
MechanicalFor elevated units, torque the frangible coupling to spec; for inset units, seat the housing flush and confirm it meets wheel-load tolerance.
Pre-Energisation Sign-off
DocumentationRecord base can position, cable route, connector seal, and subsystem/circuit assignment for every fixture as-built before backfill, since these are not inspectable once the site is closed.
Testing & Commissioning
Insulation Resistance (Megger) Test
Pre-EnergisationMegger-test each series loop across the edge, threshold, and centreline circuits before energisation, confirming insulation resistance clears the acceptable minimum.
Loop Continuity & Resistance Test
Pre-EnergisationVerify series loop continuity and record total loop resistance for each runway lighting circuit before first energisation.
Colour & Zone Transition Verification
EnergisationConfirm colour transitions between zones (white edge to red-and-white to red, or white to red at the threshold) occur at the correct distance from the runway end.
CCR Brightness Step Response
EnergisationCycle each CCR through every intensity step and confirm every fixture on its loop responds correctly, ruling out marginal transformers or loose connections.
Fixture Alignment & Aim Verification
Final AcceptanceCheck elevation and azimuth of representative fixtures across each circuit against the design aiming diagram, correcting any deviation before sign-off.
Photometric Commissioning Survey
Final AcceptanceMeasure beam intensity, colour, and beam spread with a calibrated photometer at sample points across the runway against ICAO/FAA commissioning tolerances.
Documentation & As-Built Sign-off
Final AcceptanceRecord insulation, continuity, colour-transition, and photometric readings alongside as-built layout in the commissioning dossier for handover.
Inspection & Maintenance
Fixture Damage Inspection
AnnualCheck fixtures for damage from jet blast or foreign object debris across the lighting circuit.
Photometric Output Check
AnnualMeasure light output against rated values to catch colour or intensity drift before it falls out of spec.
Circuit Intensity Balance Check
AnnualCompare intensity across fixtures on the same circuit to catch uneven output early.
Inset Fixture Seal & Drainage Check
AnnualCheck seals and drainage on inset fixtures to prevent water ingress.
Common Field Issues
Fixture Damage from Jet Blast / FOD
Inset and elevated fixtures alike are exposed to jet blast, snow-clearing equipment and general FOD; lens and housing damage is one of the most common inspection findings.
Colour or Intensity Drift Over Time
LED and lamp degradation can shift perceived colour or reduce intensity below the required threshold, which photometric field testing is designed to catch before it affects operations.
Uneven Circuit Intensity
A mix of ageing and new fixtures on the same series circuit can create visibly uneven brightness along the runway, even though each fixture is individually within tolerance.
Water Ingress in Inset Fixtures
Flush-mounted centreline and touchdown zone fixtures sit in a wet, load-bearing environment; seal failure leads to moisture ingress, corrosion, and eventual fixture failure.
Troubleshooting Guide
Fixture Cracked, Dislodged, or Missing After Winter Operations
Photometric Test Flags Colour or Intensity Below Threshold
Visibly Uneven Brightness Along a Series Circuit
Inset Fixture Fails or Shows Signs of Moisture Ingress
Failure Modes & Root Causes
Series Circuit / CCR Failure Affecting an Entire Subsystem
ALCMS Intensity-Step Command Failure
Subsystem Colour-Coding Confusion From a Wrong-Colour Fixture
Isolating Transformer / Connector Degradation at Individual Fixtures
Loop-Level Feedback Failing to Localise a Fault to a Specific Subsystem
Safety & Operational Notes
Series Circuit Isolation
Electrical SafetyEdge, threshold, centreline, and touchdown zone circuits each run on their own constant-current series loop that can carry several kV. De-energise and lock out the correct CCR for the subsystem being worked on, then verify zero energy at the fixture before opening any enclosure.
Active Runway Work Coordination
OperationalAny work on runway lighting requires ATC/airside coordination and a NOTAM where a fixture will be dark or out of tolerance; work directly on the runway surface itself needs an approved closure or a protected work window, not just a NOTAM.
Frangibility Not to Be Defeated
MechanicalNever substitute a frangible coupling or mount with a rigid fitting, and do not over-torque connections during installation or repair; runway lighting fixtures must still break away or shear cleanly on aircraft impact.
Confirm Which Subsystem You're Isolating
Electrical SafetyBecause edge, centreline, threshold, and TDZ lighting are typically on separate circuits and CCRs, positively confirm the correct feeder and circuit diagram before lockout; isolating the wrong loop can leave the fixture you're working on live while other lights go dark unexpectedly.
FOD Control on the Runway
OperationalAccount for tools, fasteners, and removed gaskets at every fixture worked on, and secure or remove loose material before reinstating, since debris on the runway can be ingested by an engine or strike an aircraft.
Insulation Test Before Re-Energisation
Electrical SafetyAfter any cable, connector, or transformer work on a runway lighting circuit, megger test the affected series loop before restoring power, since a residual fault can trip the CCR or damage healthy fixtures on the same circuit.
PPE & Grounding
Personnel SafetyUse insulated tools and appropriate PPE when working on series-circuit connections, and confirm fixtures and base cans are bonded/grounded per the electrical design before reconnecting any loop.
Restore to Compliant State
ComplianceDo not leave any subsystem with a fixture out of aim tolerance, at reduced intensity, or otherwise non-compliant; verify photometric and positional conformance before closing out the work and cancelling the associated NOTAM.
Engineering & Expert Notes
Loop Segmentation Strategy Affects Failure Blast Radius
DesignHow a runway lighting system is divided into series loops determines how much of the runway goes dark if a single loop faults. Segment loops so a worst-case single-loop failure still leaves enough usable lighting for safe operations, rather than segmenting purely for cable-run convenience.
Backup Power Transfer Time Is as Important as Backup Capacity
ReliabilityA standby generator or UPS with ample runtime doesn't help if the transfer switch takes too long to bring lighting back online during an active operation. Verify transfer time against the applicable standard's maximum outage duration, not just total backup capacity.
Size CCR Capacity With Real Growth Margin, Not Just Present Load
ElectricalSizing a constant current regulator exactly to today's connected load leaves no room for future fixture additions or LED-to-legacy mixed loops during transition. Build in a deliberate capacity margin at design stage rather than forcing a CCR replacement the next time the loop is extended.
Standardise Connector and Cable Types Before Mixed Stock Becomes the Norm
MaintenanceRunway lighting systems installed and extended over many years often accumulate mixed connector and cable types loop to loop. Standardising on a single specification for new work — even if it means an interim mismatch — keeps spares and troubleshooting simpler than letting variation compound indefinitely.
Category Match Should Be Re-Verified, Not Assumed to Carry Forward
ComplianceA runway's approach and lighting category can change with new instrument procedures or operational upgrades without a corresponding lighting system upgrade being triggered automatically. Periodically re-verify the installed lighting configuration still matches the runway's current published category.
System-Level Uniformity Checks Catch What Fixture-Level Testing Misses
VerificationEvery fixture on a runway can individually pass photometric spec while the system as a whole shows visible brightness or colour banding loop to loop. Include a system-level uniformity walk or flight check in commissioning and periodic verification, not only individual fixture testing.
Frequently Asked Questions
Short answers about runway lighting: the subsystems, colour coding, power, intensity control, standards, maintenance and common faults.
Q1What is runway lighting?
Runway lighting is the set of fixed and, in some cases, sequenced light systems that mark a runway's boundaries and key reference points. Unlike approach lighting, which guides an aircraft toward the runway, it defines the runway itself once the aircraft is over it or rolling along it.
Q2What are the main parts of a runway lighting system?
Runway edge lights, centreline lights (on precision-approach runways), threshold lights, runway end lights and touchdown zone lights. Each answers a different question for the pilot: boundaries, alignment, where the usable surface begins and ends, and where the touchdown zone is.
Q3What do the different runway light colours mean?
White marks the edges and most of the centreline, green marks the threshold and red marks the runway end. Edge lighting can change colour near the runway end and centreline lighting changes near the end on some systems, so pilots can judge remaining distance.
Q4Which runway lights are inset and which are elevated?
Edge and threshold lights are typically elevated, while centreline and touchdown zone lights are typically inset (flush-mounted).
Q5How bright are runway lights?
Typical minimums are 10,000 cd for white edge lights, 8,000 cd for green threshold and red end lights and 6,500 cd for white centreline lights. Field intensity tolerance is ±25% of rated value at each CCR step.
Q6How is a runway lighting system powered?
Fixtures run on constant-current series circuits fed by CCRs at a standard 6.6 A loop current, each fixture isolated from the loop by its own isolating transformer. Edge, threshold, centreline and touchdown zone lighting are typically on separate circuits so intensity can be controlled independently and faults isolated.
Q7How is runway light intensity controlled?
The CCR's selectable current steps (2.8 A, 3.4 A, 4.1 A, 5.2 A and 6.6 A) change the intensity of the whole circuit together. The same edge circuit can run low on a clear night and high in fog without rewiring.
Q8How is a runway lighting layout set out?
Each subsystem follows its own spacing and offset: edge lights at uniform intervals on both sides, centreline lights along the surveyed centreline, threshold and end lights in rows at each end and touchdown zone lights in paired barrettes. The whole layout is tied to a single runway survey so geometry stays consistent.
Q9Which standards apply to runway lighting?
The main references are ICAO Annex 14, FAA AC 150/5340-24 and -30, IS 7785 (Indian Standard for airfield lighting equipment and installation practice) and DGCA CAR Section 4 for Indian aerodrome lighting requirements. Always verify the current edition and your approved requirements.
Q10How often should runway lighting be inspected?
Typically annually for fixture damage inspection, photometric output checks, circuit intensity balance checks and inset fixture seal and drainage checks. Your approved maintenance programme takes precedence.
Q11What damages runway lights most often?
Jet blast, snow-clearing equipment and foreign object debris are common causes of cracked lenses, dislodged housings and missing fixtures. LED or lamp degradation can also drift colour or intensity below the required threshold, which scheduled photometric surveys are meant to catch.
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Please read before relying on any content on this page.
- Purpose and intended users. This page on Runway Lighting is an independent educational and informational reference for competent, suitably trained and authorised airfield ground lighting (AGL) and aerodrome electrical personnel. It is not professional engineering, legal or regulatory advice, and using it does not create any professional or client relationship.
- Safety. Work on series circuits, constant current regulators (CCRs), isolating transformers, cables, connectors and lighting equipment can be fatal. Always apply the aerodrome’s permit-to-work and isolation/LOTO procedures, prove dead, use correctly rated instruments and PPE, and follow the manufacturer’s instructions. Nothing here authorises work on live equipment or the bypassing of any safety device or interlock.
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