Runway lighting is not just about visibility. It is a coded visual language designed to guide pilots during critical phases of flight. Every colour used in Airfield Ground Lighting (AGL) has a specific meaning defined in ICAO Annex 14, Volume I, with the colour limits themselves set in Appendix 1.
Understanding runway lighting colour coding is essential for engineers, designers, and airport operators to ensure correct installation, regulatory compliance, and safe operations. Not every runway has every light type described here — what is provided depends on the runway’s approach category and intended operations.
- 01 Why Colour Coding Matters
- 02 Runway Edge Lights – White to Yellow
- 03 Runway Centreline Lights
- 04 Runway Threshold Lights – Green
- 05 Runway End Lights – Red
- 06 Touchdown Zone (TDZ) Lights – White
- 07 Taxiway vs Runway Colour Difference
- 08 Importance of Photometric Accuracy
- 09 Key Takeaways
- 10 Frequently Asked Questions
Runway lighting colours are not just lights. They are instructions for pilots — each colour, and every point along the runway where that colour changes, is defined by ICAO Annex 14 to communicate position, distance remaining, and alignment.
Why Colour Coding Matters
Pilots rely on quick visual interpretation, especially during the most demanding phases of flight:
Colour coding helps pilots instantly identify:
- Position
- Distance remaining
- Runway alignment
This standardised visual information reduces confusion and supports safe decision-making during critical phases of aircraft operations.
Runway Edge Lights – White to Yellow Transition
Runway edge lights define the lateral limits of the runway, with colour changing near the far end to warn pilots that the runway is ending.
Edge lights are fixed lights showing variable white, with the red and yellow exceptions above. White indicates the normal usable runway length; yellow warns pilots that the runway end is approaching. This transition is particularly important during the landing roll, helping pilots judge the remaining runway and stopping distance.
Runway Centreline Lights – White, Red/White, Red
Runway centreline lights provide precise alignment guidance, with colour progressing through three stages as the runway end approaches.
Centreline lights are not on every runway. Annex 14 provides them on Category II and III precision approach runways, recommends them on Category I precision runways (particularly for high landing speeds or where the edge-light rows are more than 50 m apart), and calls for them on runways used for take-off in very low visibility (RVR of the order of 400 m or less). On a runway shorter than 1,800 m, the alternate red/white section starts at the midpoint of the runway instead of 900 m from the end — confirm the exact rule in your Annex 14 edition.
White ensures alignment during landing, red/white indicates a caution zone, and red signals that the runway is ending. This progressive colour change provides pilots with clear distance awareness during high-speed landing and take-off operations.
Runway Threshold Lights – Green
Threshold lights are fixed, unidirectional green lights marking the beginning of the runway available for landing. They are provided on a runway equipped with edge lights (with a limited exception for non-instrument and non-precision runways where the threshold is displaced and wing bars are provided). Green threshold wing bars add conspicuity, for example on precision approach runways.
Green marks where the runway begins; red marks where it ends. Combined fittings only work as intended when oriented correctly — see the Threshold & End Lighting article for details.
Runway End Lights – Red
Runway end lights are fixed, unidirectional red lights placed at the extremity of the runway and shown in the direction of the runway. They are provided on a runway equipped with edge lights.
This is one of the most critical visual safety cues provided by the runway lighting system.
Touchdown Zone (TDZ) Lights – White
Touchdown Zone (TDZ) lights support landing accuracy. Annex 14 requires them on Category II and III precision approach runways; they are fixed, unidirectional white lights arranged as pairs of short barrettes either side of the centreline, starting at the threshold and extending toward the runway interior (to 900 m, or to the midpoint on runways shorter than 1,800 m).
TDZ lights are installed symmetrically on both sides of the runway centreline to provide consistent visual guidance.
Taxiway vs Runway Colour Difference
A clear distinction between runway and taxiway lighting is essential to prevent pilot confusion during taxiing and runway entry.
| Element | Taxiway Lighting | Runway Lighting |
|---|---|---|
| Centreline | Green (alternating green and yellow on exit taxiways near the runway) | White, transitioning to red/white and red |
| Edge | Blue | White, transitioning to yellow |
| Dominant colours | Green and blue | White, red, and yellow |
This clear colour distinction helps pilots differentiate between the runway and taxiway environment during ground operations. Red stop bars and yellow runway guard lights are further runway-protection signals not covered in this comparison.
Importance of Photometric Accuracy
Colour alone is not enough. The lighting system must also meet the required photometric characteristics:
- Correct chromaticity as per Annex 14 Appendix 1
- Proper intensity levels against the Appendix 2 isocandela diagrams
- Uniform distribution
Incorrect colour or incorrect intensity can lead to misinterpretation by pilots, particularly during low-visibility operations.
For AGL systems, colour coding and photometric performance must work together. The correct colour must be produced at the correct intensity and with appropriate uniformity to provide reliable visual guidance.
Key Takeaways
- Edge lights run white (red before a displaced threshold, seen on approach), then yellow over the last 600 m or one-third of the runway, whichever is less
- Centreline lights progress white → alternate red/white → red as the runway end approaches
- Threshold lights are green toward approach; runway end lights are red toward the runway — combined fittings give both only where the threshold is at the runway end
- TDZ lights are white, symmetrically placed either side of the centreline, and required on Category II/III precision runways
- Taxiway lighting (green centreline, blue edge) is deliberately distinct from runway colours
- Correct colour without correct chromaticity, intensity, and uniformity is not enough for reliable guidance
Runway Colour Map at a Glance
Threshold (Approach) → Runway End, Plan View. Schematic — not to scale; light counts and spacing are illustrative.
Conclusion
Runway lighting colour coding is a standardised visual communication system defined by ICAO to ensure safe and efficient aircraft operations. Each colour carries a specific meaning — from white centreline guidance to red runway-end warning, every signal is designed to support pilot decision-making in real time.
For AGL engineers and airport authorities, strict adherence to these colour codes is not optional. It is a critical requirement for safety, compliance with the applicable regulations (ICAO Annex 14 as implemented by each State, in India through DGCA requirements), operational reliability, and effective pilot guidance.
In short, runway lighting colours are not just lights. They are instructions for pilots.
Frequently Asked Questions
Why is runway lighting colour coded?
Runway lighting is a coded visual language in which every colour has a specific meaning defined in ICAO Annex 14, Volume I, with colour limits set in Appendix 1. Colour helps pilots instantly identify position, distance remaining and runway alignment during night operations, low visibility and the final approach and landing roll.
What colours do runway edge lights show?
Edge lights are fixed lights showing variable white, with two exceptions. They show red from the runway start to a displaced threshold as seen on approach, where one exists, and yellow over the last 600 m or one-third of the runway, whichever is less, at the far end. White shows the normal usable length and yellow warns that the runway end is approaching.
How do runway centreline light colours change along the runway?
Centreline lights are white from the threshold to 900 m from the runway end, alternate red and white from 900 m to 300 m from the end, and red for the last 300 m. On a runway shorter than 1,800 m the alternating section starts at the midpoint instead, so confirm the exact rule in your Annex 14 edition.
Do all runways have centreline lights?
No. Annex 14 provides them on Category II and III precision approach runways, recommends them on Category I precision runways in some cases (particularly for high landing speeds or where edge-light rows are more than 50 m apart), and calls for them on runways used for take-off in very low visibility. What is provided depends on the runway's approach category and intended operations.
What colours are threshold and runway end lights?
Threshold lights are fixed, unidirectional green lights marking the beginning of the runway available for landing. Runway end lights are fixed, unidirectional red lights facing the runway, giving a clear stop signal that helps prevent runway overrun. Where the threshold is at the runway end, one combined fitting can show green toward approach and red toward the runway.
What are touchdown zone (TDZ) lights?
TDZ lights are fixed, unidirectional white lights arranged as pairs of short barrettes either side of the centreline, starting at the threshold and extending toward the runway interior. Annex 14 requires them on Category II and III precision approach runways, and they mark the stretch where the aircraft is expected to touch down and support depth perception.
How do taxiway light colours differ from runway light colours?
Taxiway centreline lights are green (alternating green and yellow on exit taxiways near the runway) and taxiway edge lights are blue, while runway lighting uses white, red and yellow. This deliberate distinction helps pilots tell the runway and taxiway environments apart during taxiing and runway entry.
Is the correct colour enough for reliable guidance?
No. The lighting system must also meet Annex 14 Appendix 1 chromaticity limits, the Appendix 2 isocandela intensity requirements and uniform distribution. Incorrect colour or intensity can lead to misinterpretation by pilots, particularly during low-visibility operations.