Medium Intensity Runway Light
A versatile runway lighting fixture providing balanced visibility for precision and non-precision runways. Medium intensity lights offer optimal performance for CAT I precision approaches and general night operations, delivering reliable illumination across a wide range of visibility conditions.
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What Is It?
A Medium Intensity Runway Light is a versatile runway lighting fixture providing balanced visibility for precision and non-precision runways. Medium intensity lights offer optimal performance for CAT I precision approaches and general night operations, delivering reliable illumination across a wide range of visibility conditions. These lights typically utilize 45W to 65W halogen lamps or equivalent LED arrays, striking a balance between visibility and energy efficiency. They are the most common type of runway edge light, used on the majority of paved runways worldwide.
Purpose & Function
The medium intensity runway light exists to cover the operational middle ground that the great majority of runways actually sit in: enough visibility performance for CAT I approaches and routine night flying, without the cost, power draw, and thermal management overhead that high-intensity CAT II/III fixtures require. Because it is CCR-adjustable across the full 5-step range, the same fixture can be dimmed for clear-night operations to avoid dazzling pilots, or run at higher steps as visibility drops, giving airports a single fixture type that adapts to changing conditions instead of needing different hardware for different weather. That versatility, more than any single spec, is why it has become the default choice on the majority of the world's paved runways — it is the fixture that fits most situations well rather than any one situation perfectly.
Where Is It Used?
Medium intensity runway lights are the most widely used runway edge lights, found on:
- Precision approach runways (CAT I) requiring reliable visibility
- Non-precision runways with night operations
- Regional and domestic airports with moderate traffic volumes
- Military airfields requiring standard operational capability
- Runways with moderate visibility conditions
Installation & Location
Fixtures mount on a frangible coupling atop an L-867-type base can set flush with grade, or seat into an L-868-type inset base can where the surface is paved and load-rated, positioned no more than 3 m outward from the runway edge and clear of the graded runway strip's load-bearing width. As the most widely used runway edge fixture, setting-out follows the standard runway centreline survey and design spacing (60 m for precision, up to 100 m for non-precision runways), with cable run in trench or duct back to the isolating transformer pit on the runway edge series circuit.
How Does It Work?
Medium intensity runway lights operate using standard AGL principles:
- Power: Powered from the constant current series circuit via an isolating transformer (typically 45W or 65W).
- Light Source: Utilizes LED arrays or 45W/65W halogen lamps with precision optics.
- Beam Pattern: Projects a symmetric or asymmetric beam pattern to meet photometric requirements.
- Intensity Control: CCR-controlled intensity with 5 steps (2.8A to 6.6A) allows adjustment to match visibility conditions.
One fixture family, two beam geometries for different placements
CCR Series Circuit
5-step range: 2.8A → 3.4A → 4.1A → 5.2A → 6.6A, selected to match visibility conditions
Isolating Transformer
45W or 65W, matched to the fixture's power rating
Medium Intensity Fixture
LED array or 45W/65W halogen with precision optics
3° vertical × 6° horizontal — used for runway edge and centreline, visible equally from both directions
Shaped toward the approach path — used where directional guidance matters more than uniform coverage
2,000–10,000 cd Output
Beam geometry fixed at installation; intensity remains CCR-adjustable across all 5 steps
System Architecture & Control Logic
Medium intensity runway lights are not individually addressable — control is exercised at the loop level through the constant current series circuit. An ALCMS, operated by the tower or an automated visibility-linked routine, selects the required brightness step based on prevailing RVR or ATC instruction, and this command is passed to the CCR, which regulates the entire loop to the corresponding fixed current (one of 5 steps between 2.8A and 6.6A). Every fixture on that loop, via its own isolating transformer, draws from the same current and therefore burns at the same intensity simultaneously, regardless of whether an individual fixture is set up with a symmetric or asymmetric beam — beam geometry is fixed at installation and plays no part in the current the CCR sends down the loop. There is no way to dim or brighten a single fixture independently of the rest of the circuit. Fault detection is likewise loop-based: the CCR continuously monitors loop voltage against the commanded current, and a voltage rise at constant current signals increased circuit impedance — typically an open-circuit lamp or a failed isolating transformer — which is reported to the ALCMS as a loop fault rather than pinpointed to an exact fixture without further sectionalised testing.
Loop-level control governs current; beam geometry (symmetric or asymmetric) is set independently at installation
ALCMS
Selects brightness step based on RVR / ATC instruction
Constant Current Regulator
Regulates the loop to one of 5 fixed currents, 2.8A–6.6A
Series Circuit Loop
Same current for every fixture — no individual control
Isolating Transformer
Taps fixed loop current to this fixture's 45W/65W rating
Medium Intensity Fixture Output
Intensity tracks the loop step; a loop voltage rise flags an open circuit or failed transformer
Physical Construction
The fixture body is a die-cast aluminium housing, anodised or powder-coated for corrosion resistance, with the LED array or 45W/65W halogen lamp behind a glass or high-strength polycarbonate lens gasket-sealed for an IP67/IP68 rating. Elevated units bolt to a frangible coupling on an L-867 base can; inset (flush) units seat directly into an L-868 base can rated for aircraft wheel loading up to 100,000kg. Internal wiring terminates at an L-823 primary connector mating to the isolating transformer's secondary leads in its own base can, with stainless-steel fasteners and a drainage provision at the base — construction that sits squarely between the low- and high-intensity variants in the same family, using the same base-can and connector standard but sized to the mid-range lamp and transformer wattage this fixture is specified at.
Technical Parameters
| Parameter | Typical Value |
|---|---|
| Light Source | LED array or 45W / 65W halogen |
| Colour | White (standard), Yellow (last 600m / 2,000ft on instrument runways, or last third if shorter) |
| Luminous Intensity | 2,000 – 10,000 candela (depending on setting) |
| Intensity Steps | 5-step (2.8A – 6.6A) CCR controlled |
| Beam Pattern | Symmetric (3° vertical x 6° horizontal) or asymmetric for approach |
| Mounting Type | Elevated (frangible) or Inset (flush) |
| Load Capacity (inset) | 100,000 kg (220,000 lbs) wheel load |
| Isolating Transformer | 45W / 65W (6.6A series circuit) |
| Protection Class | IP67 / IP68 (submersible) |
| Operating Temperature | -40°C to +55°C |
Electrical Requirements
| Requirement | Typical Value |
|---|---|
| Circuit Type | Series circuit, constant current (CCR fed) |
| Rated Series Current | 6.6A (5-step: 2.8A / 3.4A / 4.1A / 5.2A / 6.6A) |
| Isolation | Via dedicated isolating transformer (45W/65W), not directly connected to series loop |
| Transformer Secondary | Matched to fixture wattage; sized to series circuit rating |
| Cable Type | L-824 single-conductor, direct-burial rated, 5kV or 600V per circuit design |
| Connector | L-823 primary connector, submersible-rated splice |
| Insulation Resistance | ≥ 50 MΩ (megger test, cable-to-ground) |
| Earthing/Grounding | Fixture body and base can bonded to airfield earth grid |
| Fault Protection | CCR-level ground fault and open-circuit detection |
| Power Source | CCR output, regulated per ICAO/FAA intensity step schedule |
Photometric Requirements
| Parameter | Typical Value |
|---|---|
| Main Beam Intensity (White) | ≥ 6,500 cd on-axis, up to 10,000 cd at full intensity |
| Main Beam Intensity (Yellow, Last 600m) | ≥ 6,500 cd on-axis, matched to the white setting for a consistent step transition |
| Beam Pattern | Symmetric (3° vertical × 6° horizontal) or asymmetric for approach-adjacent installations |
| Vertical Beam Spread | ± 2° about the fixture's set elevation |
| Isocandela Distribution | Per ICAO Annex 14 Attachment A / FAA AC 150/5340-30 figures for medium-intensity runway lights |
| Chromaticity | Within ICAO Annex 14 white or yellow boundary as applicable (CIE coordinates) |
| Intensity Tolerance | ± 25% of rated value at each CCR step (field measurement) |
| Maintenance Factor | ≥ 50% of new-fixture intensity before lamp/lens replacement is due |
| Test Method | Mobile photometric van/goniophotometer or fixed test bench per fixture |
Applicable Standards
ICAO Annex 14
Medium intensity light requirements for CAT I and non-precision runways
FAA AC 150/5345-46
Specification for medium intensity runway lights
IEC TS 61827
Characteristics of inset and elevated luminaires used on aerodromes and heliports
FAA AC 150/5345-53
Airport Lighting Equipment Certification Program - photometric testing and certification requirements applicable to LED and other AGL fixtures
Installation Requirements
Base Can Excavation & Grade
CivilExcavate and compact the sub-grade before setting the L-867/L-868-type base can flush with grade, positioned no more than 3 m outward from the runway edge and clear of the graded strip's load-bearing width.
Setting-Out to Design Spacing
CivilSet out fixture positions from the runway centreline survey at the design spacing (60 m for precision, up to 100 m for non-precision runways).
Duct & Cable Route
ElectricalLay the series circuit duct/cable route to design depth and separation, running trench or duct back to the isolating transformer pit on the runway edge series circuit.
L-823 Connector Termination
ElectricalTerminate and seal the primary connector per manufacturer procedure, keeping the splice submersible-rated before backfill.
Isolating Transformer Matching
ElectricalConfirm the isolating transformer wattage and ratio match the fixture and the series circuit's rated current step before connection.
Frangible Coupling Fixing
MechanicalTorque the frangible coupling or fixture fixing bolts to the specified value, confirming the fitting shears as designed under lateral load.
Elevation & Aim Setting
MechanicalSet fixture height and beam aim against the design aiming diagram before backfill or final pavement reinstatement.
Pre-Energisation Sign-off
DocumentationRecord base can position, cable route, connector seal, and torque values as-built before backfill.
Testing & Commissioning
Insulation Resistance (Megger) Test
Pre-EnergisationMegger-test the isolating transformer and series loop before the circuit is energised, confirming insulation resistance clears the acceptable minimum.
Loop Continuity & Resistance Test
Pre-EnergisationVerify series loop continuity end to end and record total loop resistance, ruling out open circuits or high-resistance splices.
Primary/Secondary Voltage Verification
EnergisationWith the CCR energised, confirm secondary voltage at the fixture's isolating transformer matches the rated ratio at the commissioned current step.
CCR Brightness Step Response
EnergisationCycle the CCR through all 5 intensity steps (2.8A to 6.6A) and confirm the fixture responds correctly at each.
Beam Geometry Verification
Functional TestConfirm the fixture's beam pattern (symmetric or asymmetric) matches its intended placement in the design layout.
Photometric Commissioning Test
Final AcceptanceMeasure beam intensity, colour, and beam spread with a calibrated photometer against ICAO/FAA commissioning tolerances.
Fixture Alignment & Aim Verification
Final AcceptanceCheck elevation and azimuth of each fixture against the design aiming diagram, correcting any deviation before sign-off.
Documentation & As-Built Sign-off
Final AcceptanceRecord insulation, continuity, voltage, and photometric readings alongside as-built position in the commissioning dossier for handover.
Inspection & Maintenance
Lens Cleaning
QuarterlyClean the lens of rubber deposits and debris to maintain light output.
Lamp / LED Module Output Check
AnnualVerify light output against rated values to catch degradation before it falls out of spec.
Frangible Coupling Inspection
AnnualFor elevated fixtures, check the frangible coupling for fatigue and confirm it shears freely if struck.
Seal & Gasket Inspection
AnnualCheck seals and gaskets for degradation that could let moisture into the fixture.
Common Field Issues
Lens Contamination
Medium intensity lights are exposed to rubber deposits, dust, and de-icing fluids. Regular cleaning with approved solvents and soft brushes is required to maintain light output and beam pattern integrity.
Lamp/LED Module Degradation
Halogen lamps experience gradual lumen depreciation, while LED modules can suffer from thermal degradation. Regular photometric testing and replacement of degraded light sources is essential.
Frangible Coupling Fatigue (Elevated)
Elevated medium intensity lights rely on frangible couplings that can fatigue over time. Regular inspection and replacement of couplings is recommended to ensure breakaway performance.
Troubleshooting Guide
Reduced Light Output or Altered Beam Pattern
Gradual Decline in Photometric Output
Fixture Leaning or Misaligned (Elevated Installations)
Failure Modes & Root Causes
Lens Contamination
Lamp / LED Lumen Depreciation
Frangible Coupling Fatigue
Safety & Operational Notes
Series Circuit Isolation
Electrical SafetyMedium intensity runway lights run on a constant-current series circuit that can carry several kV across the loop. De-energise and lock out the CCR, then verify zero energy at the fixture before opening a base can or handling cable connectors.
Airside Work Coordination
OperationalAny work on or near an active runway requires ATC/airside coordination and a NOTAM where the fixture will be dark or out of tolerance, with vehicle and personnel movement kept clear of the runway strip per the aerodrome's safety management procedures.
Frangibility Not to Be Defeated
MechanicalNever substitute the frangible coupling with a rigid fitting or over-torque it during installation or repair; the coupling must still shear cleanly on aircraft impact to limit damage under the frangibility requirement, particularly on elevated installations.
Hot Lamp / Housing Contact
Personnel SafetyAllow the fixture housing and lamp/LED module to cool before handling after an active period; halogen units in particular retain significant heat and can cause burns during lens or lamp replacement.
FOD Control at the Base Can
OperationalKeep tools, fasteners, and removed gaskets accounted for at all times when the base can is open, and secure or remove any loose material before reinstating the fixture, to prevent foreign object debris on the movement area.
Insulation Test Before Re-Energisation
Electrical SafetyAfter any cable, connector, or transformer work, megger test the affected series loop before restoring power, since a residual fault at re-energisation can trip the CCR or damage healthy fixtures on the same circuit.
PPE & Grounding
Personnel SafetyUse insulated tools and appropriate PPE when working on series-circuit connections, and confirm the fixture and base can are bonded/grounded per the electrical design before reconnecting the loop.
Restore to Compliant State
ComplianceDo not leave a fixture out of aim tolerance, at reduced intensity, or otherwise non-compliant after maintenance; verify photometric and positional conformance before closing out the work and cancelling the associated NOTAM.
Engineering & Expert Notes
Step Setting Should Match Reported Visibility, Not Default Habit
OperationalMedium intensity systems typically offer several brightness steps; operators sometimes leave the CCR at a habitual mid-step rather than adjusting for actual reported visibility. Confirm step selection against current conditions during commissioning checks and spot audits, not just at initial setup.
Heat Cycling Fatigues Connectors Faster Than Steady-State Circuits
ElectricalThe repeated heating and cooling from step changes on a series circuit places more thermal cycling stress on crimped and plug connectors than a steady-state circuit would. Inspect connector crimps for fatigue at overhaul rather than assuming a connector that passed initial insulation testing will stay sound indefinitely.
Elevated and Inset Variants Need Different Mechanical Checks
MechanicalMedium intensity runway lighting is specified in both elevated and inset variants depending on runway category; don't apply a single mechanical inspection checklist to both, since elevated units need mast/frangible-coupling checks that inset flush units don't, and inset units need flushness checks elevated ones don't.
Uniformity Between Adjacent Loops Needs Design-Stage Balancing
DesignWhere medium intensity runway lights are split across multiple series loops from separate CCRs, unequal loop lengths can leave one loop measurably dimmer than its neighbour at the same nominal step, even with every individual fixture in spec. Balance loop impedance at the design stage rather than after a pilot report.
De-Icing Exposure Degrades Seals Faster on High-Traffic Runways
DurabilityRunways served by medium intensity lighting often see regular de-icing fluid application; glycol-based fluid ages gaskets and lens seals faster than weather alone. Specify glycol-rated seal materials and check gasket condition at overhaul rather than only after a reported moisture ingress fault.
Track Which Step Trips a Loop, Not Just That It Tripped
TroubleshootingA loop that only nuisance-trips at the highest brightness step often points to a marginal connection or undersized component that's fine at lower current but fails under peak load. Logging which step precedes a trip narrows the fault faster than treating every trip as a generic loop fault.
Frequently Asked Questions
Short answers about medium intensity runway lights: use, intensity, mounting, standards, maintenance and common faults.
Q1What is a medium intensity runway light?
A medium intensity runway light is a versatile runway edge fixture that gives balanced visibility for CAT I precision and non-precision runways. It is the most widely used runway edge light and suits general night operations.
Q2Where are medium intensity runway lights used?
They are found on CAT I precision approach runways, non-precision runways with night operations, regional and domestic airports with moderate traffic, and military airfields with standard operational capability.
Q3How bright is a medium intensity runway light?
Output is about 2,000 to 10,000 cd depending on the setting, with at least 6,500 cd on-axis for white. The CCR steps the loop through 2.8 A, 3.4 A, 4.1 A, 5.2 A and 6.6 A.
Q4What colour are medium intensity runway edge lights?
They are white, with the last 600 m (2,000 ft) of instrument runways yellow (or the last third of the runway if that is shorter under ICAO). The yellow setting is matched to the white for a consistent step transition.
Q5What isolating transformer does a medium intensity runway light use?
Typically a 45 W or 65 W isolating transformer on the 6.6 A series circuit, feeding an LED array or a 45 W/65 W halogen lamp.
Q6What is the difference between elevated and inset medium intensity runway lights?
Elevated fixtures mount on a frangible coupling above an L-867-type base can, while inset fixtures seat in an L-868-type base can on paved, load-rated surfaces. Elevated units are positioned no more than 3 m outward from the runway edge.
Q7Which standards apply to medium intensity runway lights?
The main references are ICAO Annex 14, FAA AC 150/5345-46, IEC TS 61827 and FAA AC 150/5345-53. Always verify the current edition and your aerodrome's approved requirements.
Q8How often should medium intensity runway lights be maintained?
Typical intervals are quarterly lens cleaning and annual lamp or LED module output checks, frangible coupling inspection (elevated fixtures) and seal and gasket inspection. Your airport's approved maintenance programme takes precedence.
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Please read before relying on any content on this page.
- Purpose and intended users. This page on Medium Intensity Runway Light is an independent educational and informational reference for competent, suitably trained and authorised airfield ground lighting (AGL) and aerodrome electrical personnel. It is not professional engineering, legal or regulatory advice, and using it does not create any professional or client relationship.
- Safety. Work on series circuits, constant current regulators (CCRs), isolating transformers, cables, connectors and lighting equipment can be fatal. Always apply the aerodrome’s permit-to-work and isolation/LOTO procedures, prove dead, use correctly rated instruments and PPE, and follow the manufacturer’s instructions. Nothing here authorises work on live equipment or the bypassing of any safety device or interlock.
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