What does each AGL colour mean, and where is it used?
Colour is the first thing a pilot reads on an airfield at night. White, yellow, green, red and blue each carry a fixed meaning, so the colour of a light says what kind of surface it marks and what to do next.
Airfield ground lighting uses five colours, and each one has a job. A pilot reads the colour before any sign or marking, so the colour of a light tells them what kind of surface it marks and what to do next. This entry is a map of the whole code: what each colour means, and where on the airfield it appears.
1One job for each colour
White is the runway and the general case. Yellow means caution. Green means a safe path, or the start of usable runway. Red means stop or danger. Blue means the edge of a taxiway. Because blue is kept for taxiways and white for runways, a pilot can tell a runway edge from a taxiway edge at a glance.
2On the runway
Edge lights are white. Near the runway end they turn yellow as a caution that usable runway is running out: under ICAO the last 600 m or one-third of the runway, whichever is less. Threshold and wing bar lights are green, and runway end lights are red. The centreline is white, then alternates red and white, then turns red, as a distance-to-go cue. Touchdown zone lights are white. Where a threshold is displaced, the edge lights before it show red in the approach direction.
3On the approach
Approach centreline lights and crossbars are white. On a precision approach the inner part also has red side rows. A PAPI uses colour as the message itself: white means above the slope and red means below it, so two white and two red is on slope.
4On taxiways and at holding positions
Taxiway edge lights are blue and centreline lights are green. On a taxiway that leaves the runway, the centreline alternates green and yellow from where it starts near the runway centreline out to the edge of the ILS/MLS critical/sensitive area or the lower edge of the inner transitional surface, whichever is farther from the runway, and is all green beyond that. It tells the pilot the runway environment is close. A stop bar is a row of red lights across the taxiway, switched by air traffic control, and yellow guard lights and intermediate holding lights add caution. Fixed red lights fence off an unserviceable area.
5Signs, obstacles and beacons
Signs follow the same logic: mandatory signs are white on red, information and direction signs are black on yellow, and location signs are yellow on black. Obstacle lights are red or white by intensity class: low-intensity lights are fixed red and high-intensity lights flash white. An aerodrome beacon flashes white alternating with green on a land aerodrome, and white alternating with yellow on a water aerodrome.
| Where | Colour | Note |
|---|---|---|
| Runway edge | White; yellow near the end | ICAO: last 600 m or one-third of the runway, whichever is less. FAA: last 2,000 ft or half, whichever is less |
| Runway centreline | White, then red/white, then red | ICAO: alternating from 900 m to 300 m from the end (from the runway midpoint on runways under 1,800 m), red for the last 300 m. FAA: 3,000 ft and 1,000 ft |
| Touchdown zone | White | Paired barrettes either side of the centreline |
| Threshold and wing bars | Green | Seen from the approach |
| Runway end | Red | Seen from the runway |
| Approach centreline and crossbars | White | Sequenced flashing lights are white too |
| Approach side rows (Cat II/III) | Red | Inner part of a precision approach |
| PAPI | White above the slope, red below | A bar of four units beside the runway, white nearest the runway; two white and two red is on slope |
| Taxiway edge | Blue | Omnidirectional |
| Taxiway centreline | Green; green and yellow near the runway | Alternates from the runway out to the ILS/MLS critical/sensitive area edge or the inner transitional surface, whichever is farther |
| Stop bar | Red | Across the taxiway at a holding position, switched by ATC |
| Guard and intermediate holding lights | Yellow | Runway guard lights flash alternately |
| Unserviceability lights | Red | Fixed lights fencing off an unfit area |
| Obstacle lights | Red or white | Low-intensity: fixed red. Medium: red or white. High: flashing white |
| Aerodrome beacon | White and green (land); white and yellow (water) | ICAO: 20 to 30 flashes a minute |
| Signs | White on red; black on yellow; yellow on black | Mandatory; information and direction; location |
6Each colour is a region on the chart
A colour is not a single shade. Each one is defined as a region on the CIE chromaticity chart, and a light passes if its measured x, y point lies inside the region for its colour. Colour is checked separately from candela, and a filtered lamp and an LED can both comply.
Frequently Asked Questions
Q1What do the main AGL colours mean?
White marks the runway and is the general colour, yellow means caution, green means a safe path or the start of usable runway, red means stop or danger, and blue marks the edge of a taxiway. A pilot reads the colour before any sign or marking, so it says what kind of surface a light marks and what to do next.
Q2Why are taxiway edge lights blue and runway edge lights white?
So a pilot can tell a taxiway from a runway at a glance among many lights at night. Blue is kept for taxiway edges and white for runway edges, so the two cannot be mistaken for each other.
Q3Why do runway edge lights turn yellow near the end?
The yellow section is a caution that the usable runway is running out. Under ICAO Annex 14 it covers the last 600 m or one-third of the runway length, whichever is less. The FAA uses the last 2,000 ft or half the runway, whichever is less, on instrument runways.
Q4Why does the runway centreline change from white to red?
It is a distance-to-go cue. Under ICAO the lights are white until 900 m from the runway end, alternate red and white from 900 m to 300 m (from the runway midpoint on runways shorter than 1,800 m), and are red for the last 300 m. The FAA sequence is the same idea, using 3,000 ft and 1,000 ft.
Q5Are the ICAO and FAA colours the same?
The colours and their meanings are the same in nearly every case. The differences are in distances and details, such as the length of the caution zone and the centreline sequence, so check the standard that applies to your aerodrome.
Q6How is the colour of a light checked?
Each colour is a region on the CIE chromaticity chart. A spectroradiometer or colorimeter measures the light's x, y point, and the light passes if the point lies inside the region for its colour. Colour is checked separately from candela, and both filtered lamps and LEDs can comply.
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