RUNWAY EDGE LIGHT VS RUNWAY CENTRELINE LIGHT
Two Runway Lighting Systems, Two Different Visual Guidance Jobs — edge lights define the lateral limits of the runway, while centreline lights define the longitudinal alignment down its length. Both are core runway lighting systems, but they answer different questions for the pilot.
At a Glance
| Parameter | Runway Edge Light | Runway Centreline Light |
|---|---|---|
| Main purpose | Defines runway edges | Defines runway centreline |
| Installation | Along both sides of runway | Along runway centreline |
| Mounting | Usually elevated or inset | Normally inset/flush |
| Pilot guidance | Lateral runway limits | Longitudinal alignment |
| Typical colour | White | White, with colour changes near runway end |
| Approach direction | Same basic edge indication | Colour sequence depends on direction |
| Inset required | Not always | Typically required |
| Aircraft wheel clearance | Outside runway surface | Must withstand aircraft wheel loads |
| Main use | Take-off and landing | Take-off and landing, especially low visibility |
| Importance in low visibility | High | Very high |
Runway Edge Lights: Physical Layout
Runway Edge Lights are installed along the edges of the runway, running the full length on both sides.
Runway Edge Lights (gold) run along both sides of the runway, marking its usable lateral width.
They visually define: "This is the usable lateral width of the runway."
Runway Centreline Lights: Physical Layout
Runway Centreline Lights are installed along the longitudinal centreline of the runway, in a single line down its length.
Runway Centreline Lights (cyan) run down the longitudinal centreline, providing continuous alignment guidance.
They provide: longitudinal alignment and directional guidance along the runway centreline.
Where the Fixture Sits
Edge Light
The light is generally located beside the runway edge, outside the surface used by aircraft wheels.
Centreline Light
The light is installed in the pavement itself. Centreline lights are normally inset because aircraft wheels can pass directly over them.
Runway Edge Light Colours
The normal runway edge-light indication is white. However, on precision instrument runways, the colour indication changes near the runway end.
A common ICAO arrangement: white along the runway length, changing to yellow/amber near the runway end to warn the pilot of the approaching threshold from the far side.
The exact colour pattern and length depend on the applicable runway lighting standard and runway type.
Runway Centreline Light Colours
Centreline lights have a more detailed colour sequence than edge lights.
| Zone (approaching runway end) | Typical Colour |
|---|---|
| Main runway length | White |
| Approaching runway end | Alternating white and red |
| Final segment before runway end | Red |
The purpose is to provide increasing visual warning that the aircraft is approaching the runway end. For a specific project, the exact spacing and colour sequence should be checked against the applicable ICAO Annex 14 / national standard.
What Question Does Each System Answer?
Edge Light
Where are the runway boundaries?
Centreline Light
Where is the runway centreline?
What the Pilot Actually Sees
Edge Lights
The pilot sees two parallel lines of lights converging toward the horizon, establishing the runway width and its lateral boundaries.
Centreline Lights
The pilot sees a single line of lights extending straight ahead, helping maintain longitudinal alignment down the runway.
In reduced visibility, the edges may be difficult to distinguish. The centreline then provides the strongest single reference for maintaining runway alignment.
Elevated vs Inset
Edge Light
Can commonly be elevated or inset, depending on the runway design and applicable requirements.
Centreline Light
Normally inset and flush with the pavement, because aircraft operate directly over the centreline.
Why Mounting Differs: The Engineering Reason
This is a major engineering difference between the two systems.
Edge Light
The unit is generally outside the aircraft wheel path. Therefore, elevated fixtures can be used where permitted.
Centreline Light
The fixture is located directly in the aircraft operating area. It must therefore be designed to withstand:
- Aircraft wheel loads
- Pavement loading
- Impact
- Jet blast
- Environmental conditions
- FOD considerations
Hence the widespread use of inset runway centreline fixtures.
Installation Parameters
| Parameter | Edge Light | Centreline Light |
|---|---|---|
| Location | Runway sides | Runway centre |
| Aircraft wheel path | Generally outside | Directly in path |
| Typical fixture | Elevated/inset | Inset |
| Pavement cutting | Lower for elevated type | Required for inset |
| Mechanical loading | Lower | High |
| Maintenance access | Easier for elevated | More involved |
| Drainage | Less critical | Important for inset units |
| Alignment | Horizontal/vertical positioning | Precise centreline positioning |
Electrical Engineering Perspective
Both systems commonly use series-circuit AGL architecture with isolation transformers.
Typical architecture: CCR → series circuit → isolation transformer → light unit. Runway centreline circuits typically feed a longer chain of individually transformed inset fixtures along the runway length.
The exact circuit configuration depends on the airport's AGL design.
What Gets Checked, and How Often
Edge Lights
- Lamp/LED operation
- Lens condition
- Alignment
- Frangibility where applicable
- Cable/transformer condition
- Photometric performance
- Fixture damage
Centreline Lights
All edge-light checks apply, plus additional attention to:
- Inset fixture condition
- Lens damage
- Water ingress
- Drainage
- Pavement seal
- Fixture height relative to pavement
- Aircraft-load damage
- Isolation transformer condition
Full Engineering Parameters
| Area | Runway Edge Light | Runway Centreline Light |
|---|---|---|
| Guidance | Runway boundary | Runway alignment |
| Position | Both sides | Centreline |
| Main visual function | Defines width | Defines longitudinal axis |
| Typical colour | White | White + colour coding near end |
| Fixture type | Elevated or inset | Predominantly inset |
| Aircraft wheel loading | Lower | High |
| Low visibility importance | High | Very high |
| Maintenance | Relatively simple | More demanding |
| Civil work | Lower for elevated | Higher |
| Drainage | Moderate | Critical for inset |
Myths vs Facts
They serve different visual functions. Edge lights define lateral boundaries; centreline lights define longitudinal alignment. Neither substitutes for the other.
Centreline lights sit directly in the aircraft wheel path and are normally inset for that reason. Edge lights, being outside that path, have more flexibility in mounting.
Requirements depend on the specific runway, approach type and applicable standard. Runway edge lighting is more universally provided; centreline lighting requirements vary by runway category and design.
Edge lights typically use a simpler white-to-amber/yellow transition, while centreline lights use a more detailed white-to-red sequence to give progressive warning of the runway end.
Runway Edge Light vs Runway Centreline Light
Runway Edge Lights and Runway Centreline Lights are complementary, not interchangeable. Edge lights answer where the usable runway surface ends sideways; centreline lights answer where the aircraft should stay aligned along its length.
Together, both systems form the core visual guidance that lets a pilot judge width, alignment and remaining runway distance — particularly critical when visibility is reduced.
Edge = Width. Centreline = Alignment. The exact configuration, colour sequence and inset requirements for a specific project should always be checked against ICAO Annex 14 or the applicable national standard.
Engineering & Expert Notes
Check Drainage and Seals on Inset Centreline Lights
WaterWater damage is common.
Verify Alignment
AlignmentCheck aim and level.
Check Colour
ColourVerify chromaticity.
Walk the Pattern at Night
InspectionLook for gaps.
Frequently Asked Questions
Edge lights define the lateral limits of the runway (its usable width), while centreline lights define the longitudinal centreline that the aircraft should follow down the runway.
Centreline lights sit directly in the path of aircraft wheels, so they must be flush and able to withstand wheel loads, impact and jet blast. Edge lights sit outside the runway surface, giving more flexibility in mounting.
No. The requirement depends on the specific runway, approach category and the applicable governing standard — it should not be generalized across all runways.
Normally white, though the indication may change to yellow/amber near the runway end on precision instrument runways, depending on the applicable standard.
A typical ICAO arrangement transitions from white, to alternating white and red, to solid red closest to the runway end — giving the pilot increasing warning of the remaining runway distance.
Centreline lighting becomes particularly important in low visibility, since it can provide a strong single line of reference when the runway edges are difficult to distinguish. Edge lighting importance remains high as well.
Governing Documents
For an actual project design, always verify the current edition of the applicable documents.
FAA AC 150/5340-30
Design and Installation Details for Airport Visual Aids — installation guidance for runway edge, centreline and touchdown zone lighting systems.
FAA AC 150/5345-46
Specification for Runway, Taxiway, Heliport, and Vertiport Light Fixtures — the equipment spec governing elevated and inset fixture construction, including wheel-load and frangibility requirements.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — runway edge light and centreline light characteristics, colour coding, spacing and applicability by runway type.
DGCA / AAI Requirements
For Indian airport projects, also verify applicable DGCA requirements, AAI requirements, airport-specific technical specifications, project drawings and contract specifications.
Final Engineering Note
Do not design a runway lighting system from a generic web diagram. The final installation drawing should always be developed from the current governing standard, approved airport design and project-specific requirements.
Edge lighting and centreline lighting are two halves of the same visual guidance picture — one marks the boundary, the other marks the line to follow.
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