Runway Lighting
Runway Threshold Light for Airfield Ground Lighting
Clear visual identification of the beginning of the landing portion of the runway
Runway threshold lights identify the beginning of the landing portion of the runway and provide an essential visual reference to approaching aircraft. Threshold lighting must deliver the required colour, intensity, beam distribution and directional visibility for the applicable runway configuration. Precision AGL Solutions supplies runway threshold lighting selected against the approved project design, applicable standard and manufacturer technical data.
Supplied by Precision AGL Solutions
Product Overview
Runway Threshold Light
Selected According To
- Runway configuration
- Runway approach category
- Threshold arrangement
- Elevated or inset installation
- LED or other approved light-source technology
- Series-circuit requirements
- Photometric requirements
- Environmental conditions
- Applicable project specifications
- Applicable ICAO, FAA, DGCA and other governing requirements
Basis of Selection
As part of the runway visual aid system, threshold lighting must provide the required colour, intensity, beam distribution and directional visibility for the applicable runway configuration and operational requirements.
Product selection should always be based on the approved project design, applicable standard and manufacturer technical data.
Primary Applications
Where Runway Threshold Lights Are Used
Instrument runwaysThreshold identification for instrument operations.
Precision approach runwaysPart of the visual aid system for precision approach.
Non-precision approach runwaysWhere applicable to the runway configuration.
CAT I / II / III systemsRunway lighting systems for each approach category.
Threshold identification and transitionsMarks the threshold and threshold transitions.
Upgrades and replacementsModernised AGL systems and replacement of existing threshold fixtures.
New airport AGL installationsThreshold lighting for new airfield projects.
Runway rehabilitation projectsReinstatement during runway rehabilitation.
Function of Threshold Lighting
A Critical Visual Reference on Approach and Landing
What the Lights Do
The threshold is a critical visual reference during the approach and landing phase. Threshold lights give a clear visual indication of the threshold location and, depending on the applicable configuration, may form part of a combined threshold/end lighting arrangement.
The optical system is therefore as important as the mechanical fixture itself.
A Properly Selected System Provides
- Correct light colour
- Required intensity
- Correct beam orientation
- Appropriate vertical and horizontal coverage
- Adequate visibility from the approach direction
- Compatibility with the runway lighting circuit
- Reliable operation under environmental conditions
- Maintainability throughout the asset lifecycle
Typical Configurations
Elevated and Inset Threshold Lights
1. Elevated Threshold Light
Mounted above the pavement using an appropriate base, mounting arrangement or frangible support system. Useful where the approved airport design calls for above-ground visual aids.
Typical considerations
- Elevated fixture body
- Frangible mounting arrangement
- Directional optical system
- Series-circuit connection
- Mechanical protection
- Alignment with runway threshold
- Clearance from aircraft movement areas
2. Inset / In-pavement Threshold Light
Installed substantially flush with the pavement surface. Typical where an elevated fixture would interfere with aircraft movement, clearance requirements or the approved pavement configuration.
Key considerations
- In-pavement housing
- Light fixture assembly
- Optical lens
- Correct orientation
- Drainage
- Pavement interface
- Transformer connection
- Connector and cable arrangement
- Sealing against moisture and contamination
- Serviceability
The complete inset installation should be considered as an assembly, not simply as a light fitting.
Light Colour
Green, Fixed, Unidirectional Toward the Approach
Threshold Colour
Runway threshold lights are green, fixed and unidirectional, visible to aircraft on approach. On precision approach runways, green wing bars may be added on each side of the threshold for extra conspicuity. The number and spacing of lights depend on the runway type and approach category, so confirm them against the edition of Annex 14 or FAA guidance in use. ICAO Annex 14 requires threshold lights on a runway equipped with runway edge lights, except on a non-instrument or non-precision runway with a displaced threshold where wing bar lights are provided.
Combined Threshold/End Fixtures
Many installations use one fixture that shows green toward the approach and red toward the runway. FAA types include L-862E (high-intensity elevated), L-861E (medium-intensity elevated) and L-850D (inset). Displaced thresholds need a different arrangement, so follow the approved layout and confirm the lens orientation on the order.
Optical & Photometric Performance
Threshold Lights Are Precision Optical Equipment
| Parameter | Engineering Requirement |
|---|---|
| Light colour | Green, unidirectional toward the approach (green/red in a combined threshold/end fixture) |
| Light source | LED or approved technology |
| Optical system | Directional / project specific |
| Beam distribution | Manufacturer and standard specific |
| Intensity | Required photometric performance |
| Horizontal coverage | Project / standard specific |
| Vertical coverage | Project / standard specific |
| Intensity steps | Where applicable |
| Colour coordinates | Applicable standard requirement |
| Optical alignment | Critical during installation |
| Photometric verification | Recommended / project dependent |
For precision approach operations, verify photometric performance against the applicable requirements rather than evaluating it solely by visual observation.
LED Light Source
LED Technology
Potential Advantages
- Long operating life
- Lower maintenance requirements
- Stable optical performance
- Reduced lamp replacement frequency
- Efficient electrical operation
- Controlled beam distribution
- Improved monitoring possibilities
- Compatibility with modern AGL control systems
Compliance Is Not Automatic
Modern threshold lighting may use LED technology for controlled optical output and improved lifecycle characteristics. However, LED technology alone does not establish compliance.
The complete fixture must meet the applicable photometric, electrical, environmental and mechanical requirements.
Electrical Characteristics
AGL Series Circuit Arrangement
Constant Current Regulator → Primary Cable → Isolating Transformer → Secondary Cable → Threshold Light
Parameters to Verify
- Rated current
- Series-circuit compatibility
- Transformer rating
- Power consumption
- Input electrical characteristics
- Intensity control compatibility
- Connector arrangement
- Cable interface
- Insulation requirements
- Earthing / bonding arrangement where applicable
- Monitoring compatibility
Why the Whole Chain Matters
Where a constant-current series circuit is used, the threshold light and associated isolating transformer must be evaluated as a coordinated system. A mismatch between fixture, transformer and circuit characteristics can result in:
- Incorrect light intensity
- Poor intensity control
- Circuit instability
- Excessive current
- Premature equipment failure
- Monitoring problems
- Incorrect photometric performance
Selection should be based on the approved AGL circuit design and manufacturer data.
Construction & Environment
Mechanical Construction and Environmental Performance
Mechanical Construction
Depending on the selected configuration, construction may include:
- Corrosion-resistant fixture body
- Optical lens assembly
- LED/light-source module
- Optical reflector or lens system
- Mounting arrangement
- Frangible support where required
- Gasket and sealing system
- Cable/connector interface
- Fasteners
- Inset housing where applicable
- Drainage provisions for inset installations
Confirm the exact construction from the manufacturer's technical data sheet.
Environmental Performance
Airport lighting equipment operates in demanding environments. Evaluate the fixture for:
- Water ingress protection
- Dust exposure
- Temperature variation
- Humidity
- UV exposure
- Corrosion
- Vibration
- Mechanical impact
- Chemical contamination
- Aircraft operating environment
For inset fixtures, give particular attention to pavement interface + sealing + drainage + water ingress + mechanical loading.
Comparison
Elevated vs Inset Threshold Light
| Feature | Elevated | Inset |
|---|---|---|
| Installation | Above pavement | Flush / in-pavement |
| Aircraft clearance | Must be considered | Generally suited to movement-area clearance requirements |
| Mounting | Frangible support / base | Inset housing |
| Pavement interface | Limited | Critical |
| Drainage | Standard consideration | Major consideration |
| Maintenance access | Generally accessible | Requires pavement/housing access |
| Optical alignment | Important | Critical |
| Mechanical loading | Lower fixture exposure | High pavement/environment exposure |
| Typical selection | Project specific | Project specific |
The final configuration should always follow the approved airport lighting layout.
Installation Considerations
Before Installation, Verify
Location
- Approved threshold coordinates
- Runway centreline reference
- Fixture spacing
- Threshold alignment
- Approach direction
- Runway end relationship
Orientation
- Correct optical direction
- Correct azimuth
- Correct elevation
- Correct beam alignment
- Correct colour direction
Electrical
- Correct isolating transformer
- Correct secondary connection
- Correct connector type
- Correct cable length
- Correct circuit identification
- Correct circuit current
Mechanical
- Correct mounting arrangement
- Correct torque
- Correct sealing
- Correct gasket installation
- Correct pavement interface
- Correct frangibility arrangement where applicable
Commissioning & Testing
Verify as Part of AGL Commissioning
Visual Inspection
- Fixture condition
- Lens condition
- Mounting condition
- Alignment
- Cable condition
- Connector condition
- Water/moisture evidence
- Mechanical damage
Electrical Tests
Depending on the approved test procedure:
- Circuit continuity
- Insulation resistance
- Transformer verification
- Secondary connection verification
- Circuit current verification
- CCR operation
- Intensity-step operation
Photometric Verification
Where required, verify:
- Light colour
- Intensity
- Beam distribution
- Directional coverage
- Fixture alignment
- Photometric compliance
A threshold light that is electrically operational is not automatically photometrically compliant.
Inspection & Maintenance
Inspect the Fixture and Its Installation
Fixture
- Lens cleanliness
- Lens damage
- Light output
- Housing condition
- Fasteners
- Seals
- Mounting
Electrical
- Transformer condition
- Connector condition
- Cable condition
- Circuit current
- Insulation condition
- Evidence of moisture
Inset Installation
Special attention to:
- Water accumulation
- Housing condition
- Drainage
- Gaskets
- Pavement interface
- Fixture seating
- Bolt condition
- Lens damage
- Internal contamination
Common Failure Modes
Typical Threshold-Light Problems
| Symptom | Possible Causes |
|---|---|
| Light OFF | Open circuit; failed light source; transformer failure; connector failure; cable fault; circuit interruption; fixture internal fault |
| Low light output | Incorrect CCR intensity; optical contamination; LED/light-source degradation; incorrect fixture alignment; electrical mismatch; optical component damage |
| Intermittent operation | Loose connector; moisture ingress; cable connection problem; transformer connection issue; internal fixture fault |
| Incorrect colour | Incorrect fixture configuration; optical component problem; light-source degradation; contamination; incorrect replacement component |
Engineering Troubleshooting Sequence
A Practical Diagnostic Sequence
CCRVerify output
Primary series circuitCheck circuit
Isolating transformerCheck transformer
Secondary cableCheck cable
L-823 / connector interfaceCheck approved connector
Threshold fixtureCheck fixture
Light source / opticsInspect
Photometric verificationConfirm output
This approach helps prevent unnecessary replacement of an otherwise healthy fixture.
Product Selection Checklist
Before Ordering, Confirm
- Airport / project
- Runway identification
- Runway classification
- Approach category
- Threshold configuration
- Elevated / inset requirement
- Light colour
- Directionality
- Photometric requirement
- LED / approved light-source technology
- Series-circuit current
- Isolating transformer requirement
- Connector requirement
- Mounting arrangement
- Environmental requirements
- Applicable standard
- Approved manufacturer
- Manufacturer TDS
- Type-test / compliance documentation
- Project approval requirements
Technical Submittal
Technical Data to Request from Manufacturer
For engineering review and procurement, the manufacturer should provide, as applicable:
- Product datasheet
- Photometric data
- Light distribution information
- Colour characteristics
- Electrical specifications
- Power consumption
- Operating current
- Transformer requirements
- Connector details
- Mounting details
- Dimensions
- Weight
- Material specification
- Environmental rating
- Operating temperature range
- Installation instructions
- Maintenance instructions
- Compliance certificates
- Type-test reports
- Warranty information
Safety
Electrical Safety — Isolation and Lock-Out
WARNING — never open a live series circuit. An open series circuit driven by a constant-current regulator can produce dangerously high voltage. Opening, cutting or disconnecting any part of an energised circuit can cause serious injury or death and damage equipment.
- De-energise the circuit at the regulator and apply the site lock-out / tag-out (LOTO) procedure before any work
- Where the circuit must be isolated or shorted, use the series circuit cut-out switch or approved isolation device — not an improvised bypass
- Verify the circuit is de-energised and the output is isolated before touching conductors, connectors, splices, transformers or fixtures
- Do not disconnect or reconnect a fixture's secondary connector while the series circuit is energised: an open secondary on a series isolating transformer can develop hazardous voltage and damage the transformer
- Work on the movement area only under the airport's permit-to-work system, with the runway or taxiway closed as required, using qualified personnel and the manufacturer's instructions
- Follow the applicable national electrical safety regulations and site procedures
Standards & References
Governing Standards
Select and install in accordance with the applicable edition of the governing project standards and approved aerodrome design.
- ICAO Annex 14 — Aerodromes
- Applicable ICAO aerodrome lighting provisions
- FAA AC 150/5340-30J — Design and Installation Details for Airport Visual Aids
- FAA AC 150/5345-46F — runway light fixtures (threshold/end types L-862E, L-861E elevated; L-850D inset)
- DGCA India requirements, where applicable
- Applicable Indian Standards
- Airport-specific technical specifications
- Approved project drawings
- Approved AGL lighting layout
- Manufacturer installation instructions
See the ICAO Annex 14 Guide and FAA AGL Guide for background.
Important: Verify the applicable standard edition and project specification before procurement or installation.
FAQ
Runway Threshold Light — Frequently Asked Questions
What is a runway threshold light?
Runway threshold lights identify the beginning of the landing portion of the runway and provide an essential visual reference to approaching aircraft. They must deliver the required colour, intensity, beam distribution and directional visibility for the applicable runway configuration. Depending on the configuration, they may form part of a combined threshold/end lighting arrangement.
What colour are runway threshold lights?
Runway threshold lights are green, fixed and unidirectional, visible to aircraft on approach. On precision approach runways, green wing bars may be added on each side of the threshold for extra conspicuity. The number and spacing of lights depend on the runway type and approach category, so confirm them against the edition of Annex 14 or the FAA guidance in use.
When does ICAO require threshold lights?
ICAO Annex 14 requires threshold lights on a runway equipped with runway edge lights, except on a non-instrument or non-precision runway with a displaced threshold where wing bar lights are provided.
What is a combined threshold/end fixture?
It is a single fixture that shows green toward the approach and red toward the runway. FAA types include L-862E (high-intensity elevated), L-861E (medium-intensity elevated) and L-850D (inset). Displaced thresholds need a different arrangement, so follow the approved layout and confirm the lens orientation on the order.
What is the difference between elevated and inset threshold lights?
An elevated light is mounted above the pavement using a base, mounting arrangement or frangible support, and suits designs calling for above-ground visual aids. An inset light is installed substantially flush with the pavement, typically where an elevated fixture would interfere with aircraft movement, clearance requirements or the approved pavement configuration. For inset lights the pavement interface, drainage, sealing and optical alignment are critical, and the complete installation should be considered as an assembly.
Is a threshold light that works electrically automatically compliant?
No. A threshold light that is electrically operational is not automatically photometrically compliant, and for precision approach operations photometric performance should be verified against the applicable requirements rather than judged by visual observation alone. LED technology also does not by itself establish compliance, since the complete fixture must meet the applicable photometric, electrical, environmental and mechanical requirements.
How are threshold lights powered, and why does the whole chain matter?
The arrangement is a constant current regulator, primary cable, isolating transformer, secondary cable and the threshold light. The fixture and its isolating transformer must be evaluated as a coordinated system, because a mismatch between fixture, transformer and circuit characteristics can cause incorrect light intensity, poor intensity control, circuit instability, excessive current, premature equipment failure, monitoring problems or incorrect photometric performance.
What should be verified before and during installation?
Verify the approved threshold coordinates, runway centreline reference, fixture spacing, threshold alignment and approach direction, the correct optical direction, azimuth, elevation, beam alignment and colour direction, the correct isolating transformer, secondary connection, connector, cable length and circuit current, and the mounting arrangement, torque, sealing, gaskets, pavement interface and frangibility arrangement where applicable.
How are threshold lights commissioned and maintained?
Commissioning includes visual inspection, circuit continuity, insulation resistance, transformer and secondary connection verification, circuit current, CCR operation, intensity-step operation and photometric verification where required. Maintenance covers lens cleanliness and damage, light output, housing, fasteners, seals, mounting, transformer, connector and cable condition, circuit current, insulation and moisture. For inset lights, pay special attention to water accumulation, drainage, gaskets, the pavement interface, fixture seating and bolt condition.
What are the common faults with threshold lights?
A light that is off can come from an open circuit, failed light source, transformer failure, connector failure, cable fault, circuit interruption or internal fixture fault. Low output can come from incorrect CCR intensity, optical contamination, LED degradation, incorrect alignment, electrical mismatch or damaged optics. Intermittent operation can come from a loose connector, moisture ingress or a cable or transformer connection problem, and an incorrect colour from incorrect fixture configuration, optical problems, light-source degradation, contamination or an incorrect replacement component. Work along the circuit before replacing a healthy fixture.
What should be confirmed before ordering, and which standards apply?
Confirm the airport and project, runway identification and classification, approach category, threshold configuration, elevated or inset requirement, light colour, directionality, photometric requirement, light-source technology, series-circuit current, isolating transformer, connector, mounting, environmental requirements and the manufacturer’s compliance documentation. References include ICAO Annex 14, FAA AC 150/5340-30J, FAA AC 150/5345-46F (threshold/end types L-862E, L-861E and L-850D), DGCA India requirements and airport-specific specifications. Verify the applicable edition before procurement.
Is it safe to work on a runway threshold light while the series circuit is energised?
No. An open series circuit driven by a constant-current regulator can produce dangerously high voltage, and opening, cutting or disconnecting any part of an energised circuit can cause serious injury or death. Do not disconnect or reconnect a fixture’s secondary connector while the series circuit is energised, because an open secondary on a series isolating transformer can develop hazardous voltage and damage the transformer. De-energise the circuit at the regulator, apply the site lock-out / tag-out procedure, use the series circuit cut-out switch or an approved isolation device, and work on the movement area only under the airport’s permit-to-work system, with the runway or taxiway closed as required. See the electrical safety warning on this page.
Why Precision AGL Solutions
A Complete-System Approach
We approach runway threshold lighting as part of the complete Airfield Ground Lighting system, rather than as an isolated product. Our technical approach considers:
Fixture → Optics → Transformer → Connector → Series Circuit → CCR → Photometry → Maintenance
This system-level approach supports technically appropriate product selection and helps reduce compatibility, installation and maintenance problems.
Procurement Information for Indian Projects
Indian public tenders commonly ask for the documents below. State which ones your tender requires when you send the enquiry, so they are covered in the quotation.
- Manufacturer / OEM authorisation
- Country of origin and local-content declaration (for Make in India purchase preference)
- Type-test and routine-test certificates, and the FAA / ICAO / IEC compliance documents named in the specification
- Datasheets, drawings and installation instructions
- Warranty, delivery period and spares support
- GeM catalogue or tender-portal requirements, where applicable
Need the Right Runway Threshold Light?
Have a runway lighting requirement? Send us your runway configuration, classification, approach category, existing lighting arrangement, approved BOQ, technical specification, fixture quantity, existing fixture details and required mounting arrangement. We can review it and identify the appropriate runway threshold lighting configuration for the project.
- Emailprecisionaglsolutions@gmail.com
- Websiterahulsharmaagl.in
- LinkedInPrecision AGL Solutions
- Phone+91 98214 96412
Engineering Note
Runway threshold lights are safety-critical visual aids. Product selection should not be based only on physical appearance, nominal wattage or catalogue description.
The fixture, optical performance, colour, circuit compatibility, mounting arrangement and applicable aerodrome requirements must be evaluated together before approval and procurement.
Product Disclaimer
Product availability, configuration, dimensions, electrical characteristics, photometric performance, certifications and compliance status depend on the selected manufacturer and project specification. The technical values published on this page should not be treated as a substitute for the manufacturer's current approved Technical Data Sheet.
Final selection shall be based on the approved project specification, applicable aviation standards, authority requirements, manufacturer documentation and site conditions. Use of this page is also subject to the Legal Notice, Disclaimer & Terms of Use.
Standards and editions referenced on this site are listed on the Standards Reference page.