Airport Lighting Glossary: Light Unit – Individual Lighting Fixture

Definition and Core Function

A light unit in airport lighting is an individual, purpose-engineered fixture designed to provide a specific visual function—guidance, marking, or warning—within an airfield lighting system. Each unit is manufactured to exacting international standards, such as ICAO Annex 14 and FAA Advisory Circulars, which govern optical performance, durability, environmental resistance, and installation. Light units are vital for both airside safety and operational efficiency, giving pilots and ground staff precise visual cues for navigation, even in poor visibility. Their placement and orientation form an integrated, regulated network that enables safe aircraft movement day and night.

Physically, a light unit typically consists of a robust, weather-sealed housing, advanced optics, and a resilient mounting system—either elevated or in-pavement. Modern units predominantly use LED technology for enhanced longevity, energy efficiency, and photometric accuracy. Features like dimmability, remote monitoring, and self-diagnostics are commonplace in contemporary airfield lighting.

Types of Airport Lighting Units

Airport operations require a range of specialized light unit types, each optimized for a particular role:

• Runway Lighting Units: Runway edge, threshold, end, centerline, touchdown zone (TDZ), runway end identifier lights (REIL), and runway guard lights support aircraft during landing and takeoff. Example: Edge lights use steady white, transitioning to yellow near runway ends; threshold lights use green; end lights use red.
• Taxiway Lighting Units: Taxiway edge lights (blue) and centerline lights (green) guide aircraft during ground movement.
• Approach Lighting Units: Approach lighting systems (ALS) use arrays of steady and flashing lights to help pilots align with the runway. PAPI (Precision Approach Path Indicator) units provide glide path information by color (red/white).
• Obstruction and Miscellaneous Units: Obstruction lights (red or white), airport rotating beacons, and illuminated airport signs mark hazards and provide information.

Each type is deployed according to strict standards (e.g., ICAO Annex 14, FAA ACs) for placement, color, intensity, and operational mode.

Runway Lighting Units: In-Depth

Runway Edge Lights: Placed symmetrically along both runway sides, emitting steady white (transitioning to yellow near the end). Available as elevated (frangible) or in-pavement units.

Threshold Lights: Installed at the runway threshold, emitting green toward the approach direction, often with wing bar extensions for added visibility.

Runway End Lights: Located at the far runway end, emitting red toward departing/overshooting aircraft.

Runway Centerline Lights: Embedded along the centerline, white with red/white and all-red transitions near the end for CAT II/III operations.

Touchdown Zone (TDZ) Lights: White lights in paired rows from the threshold, marking the touchdown area.

REIL (Runway End Identifier Lights): Synchronized flashing white units flanking the threshold for rapid identification.

Runway Guard Lights: Flashing or steady yellow at runway/taxiway intersections to warn of active runways.

All units must withstand environmental extremes, water ingress, and mechanical impacts per regulatory testing.

Taxiway Lighting Units

Taxiway Edge Lights: Steady blue lights along taxiway borders, typically spaced at 60 meters or closer on curves.

Taxiway Centerline Lights: In-pavement green lights marking the taxiway center, especially at complex intersections or runway exits.

Units are engineered for durability against jet blast, chemicals, and vehicle loads, with optics designed to minimize glare.

Approach Lighting Units

Approach Lighting Systems (ALS): Extensive arrays of steady and flashing white/red lights extending from the runway threshold, providing alignment and slope cues in low visibility.

PAPI Units: Rows of two or four light boxes, each projecting sharp red/white cutoffs to indicate glide path angle. Correct alignment shows two red and two white lights.

These units have the most stringent photometric and alignment requirements due to their impact on landing safety.

Obstruction and Miscellaneous Lighting Units

Obstruction Lights: Mark structures that could pose hazards, using steady or flashing red or white lights depending on structure height and criticality. Many units feature automatic intensity adjustment to reduce light pollution.

Airport Rotating Beacon: Emits alternating white/green flashes from an elevated position to indicate the airport’s location at night or in low visibility.

Illuminated Airport Signs: Internally lit signs displaying taxiway/runway designations and directions, using standardized colors and symbols for universal comprehension.

Technical Specifications and Features

Key regulated attributes of a light unit include:

• Light Output & Color: Chromaticity and intensity strictly defined by ICAO/FAA standards (e.g., CIE chromaticity boxes, HIRL/MIRL/LIRL intensity classes).
• Beam Pattern: Uni-, bi-, or omni-directional as needed.
• Mounting: Elevated (above-grade, frangible) or in-pavement (flush, load-bearing).
• Power: Typically 6.6A series circuits with isolation transformers. Solar-powered units are used in remote/temporary applications.
• Environmental Ratings: Water/dust ingress resistance (IP65+), UV, vibration, and chemical tolerance.
• Technology: Predominantly LED for energy efficiency, longevity, and photometric control; legacy units may use halogen/incandescent.
• Control & Monitoring: Integration with Airfield Lighting Control and Monitoring Systems (ALCMS), supporting remote switching, dimming, diagnostics, and pilot-controlled operation.

Functions and Operational Relevance

Each light unit contributes to:

• Visual Guidance in Low Visibility: Marking runways, taxiways, and boundaries under darkness or adverse weather.
• Runway/Taxiway Identification: Standardized color/patterns allow instant recognition of active routes.
• Approach/Landing Assistance: ALS and PAPI units provide critical orientation and slope guidance.
• Obstacle Marking: Preventing collisions with non-apparent hazards.
• Energy Efficiency & Reliability: LED/solar units lower operational costs and improve sustainability.
• Redundancy: Series circuits and transformers ensure system continuity despite individual unit failures.

Application Scenarios

Example Product: LED Elevated Runway Edge Light

Visual Reference: Airfield Lighting Layout

Compliance Standards and References

Airport light units must comply with:

• ICAO Annex 14, Volume I: The global standard for airfield lighting performance, color, installation, and maintenance.
• FAA AIM and AC 150/5345 Series: U.S. specifications for fixture certification, installation, and maintenance.
• Environmental/Safety Certifications: ETL, cULus, Energy Star, and other marks for safety and efficiency.

For further details, refer to:

• ICAO Annex 14: Aerodrome Design and Operations
• FAA Advisory Circulars 150/5345 Series

Summary

A light unit is the foundational building block of any airport lighting system. Whether marking a runway edge, guiding a taxiway, or warning of obstacles, each unit’s design, placement, and operation are governed by rigorous international standards to ensure the highest levels of safety and efficiency for airside operations.

For more information or to discuss upgrading your airfield lighting, please contact us or schedule a demo .