LED Module
The solid-state light source that powers modern AGL fixtures. Combining high-efficiency LEDs, thermal management, and precise optics, LED modules offer superior energy savings, long life, instant restart, and excellent colour stability compared to traditional halogen lamps.
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What Is It?
An LED Module is a complete solid-state light engine specifically designed for AGL applications. It consists of one or more high-power LEDs mounted on a metal-core printed circuit board (MCPCB) with integrated drive circuitry, thermal management, and optical alignment features. Unlike traditional halogen or incandescent lamps, LED modules produce light through electroluminescence, offering significantly higher efficacy (lumens per watt), longer operational life (up to 50,000 hours), and instant restart capability. LED modules are available in various colours (white, green, red, yellow, blue) and intensities, and are the standard light source for modern LED-based AGL fixtures.
Purpose & Function
The LED module's purpose is to be the actual light-emitting element that gives the pilot the visual signal the fixture exists to provide — the correct colour, correct intensity, and correct beam coordinates that ICAO Annex 14 and FAA specifications define for that fixture type. Its practical value over a halogen lamp is reliability at scale: because an airfield's safety case depends on hundreds of individual lights all working simultaneously, an LED module's longer life (up to 50,000 hours) and instant restart capability directly translate into fewer failed lights, fewer maintenance visits, and a lower chance of a gap appearing in a runway or approach lighting pattern that a pilot is using for guidance.
Where Is It Used?
LED modules are used in all modern AGL fixtures that utilise LED technology, including:
- Runway Edge & Centreline Lights: High-intensity white or yellow modules for precision guidance.
- Threshold & End Lights: Green and red modules with precise colour coordinates.
- Taxiway Lights: Blue and green modules for edge and centreline guidance.
- Approach Lighting: High-flux white modules for barrettes and flashing lights.
- PAPI & VASI: Specialised modules that produce the required red/white transition.
- Obstruction Lights: Red and white modules for aviation obstruction marking.
- Beacons & Wind Cones: LED modules for rotating beacons and illuminated windsocks.
Installation & Location
The module is bolted or clipped onto the heat sink at the fixture's optical focus, with thermal interface material applied at the mounting face so heat generated at the LED junction conducts away efficiently rather than building up behind the emitter. Its position and orientation are set to the manufacturer's optical alignment marks so the emitter sits precisely where the reflector or prism expects it; even a small offset here can shift or distort the projected beam pattern. Wiring is terminated to the module's connector before the housing is closed, with the leads kept clear of the optical path, and the module is seated so its face is protected behind the lens and gasket once the fixture is resealed.
How Does It Work?
An LED module works by passing current through a semiconductor junction, which emits light through electroluminescence. The module includes:
- LED Chips: High-power semiconductor die that emit light at specific wavelengths (colours).
- MCPCB: Metal-core printed circuit board that provides electrical connections and thermal spreading.
- Drive Circuitry: Constant-current driver that regulates current (typically 350mA to 1A per LED) for stable light output.
- Thermal Management: Heat sink or thermal pad to dissipate heat and maintain junction temperature within limits.
- Optical Alignment: Precision placement and lens/reflector integration to achieve the required beam pattern.
The module is powered by the series circuit through an isolating transformer, with intensity controlled by the CCR's current steps. LED modules are designed to meet the photometric requirements of ICAO Annex 14 and FAA specifications.
From Current to Compliant Beam & Control Logic
Current Enters Through the MCPCB
Metal-core PCB routes power to each LED chip
Semiconductor Junction
Electroluminescence converts current directly into light
Heat Generated at the Junction
Must be removed to protect chip life and output
Heat Sink / Thermal Pad
Spreads heat into the MCPCB and fixture housing
Optical Alignment
Chip positioned precisely relative to the lens or reflector
Every Function Traces Back to One Constraint — Junction Temperature Must Stay Within Limits for the Rated 50,000-Hour Life
Physical Construction
The module is built around a metal-core printed circuit board (MCPCB), usually aluminium-clad, which carries the LED die array and spreads heat efficiently from the emitters toward the heat sink mounted directly behind it. High-power LED packages are surface-mounted and, in many AGL modules, individually binned for colour and output so the array delivers consistent chromaticity and intensity across the beam. A secondary optic — a moulded lens, dome, or array of individual micro-lenses over each LED — sits over the emitter array to begin shaping the beam before the light reaches the fixture's main prism or reflector, and locating pins or a keyed mounting frame fix the module's rotational and lateral position relative to that downstream optic. The MCPCB is bolted or clipped to the heat sink through a thermal interface layer, and wiring exits the module through a sealed, often locking, connector so the module can be swapped without disturbing the potted or soldered LED-to-board joints.
Technical Parameters
| Parameter | Typical Value |
|---|---|
| Light Source Type | High-power LED (single or multi-chip) |
| Colour Options | White (4000K-6500K), Green, Red, Yellow, Blue |
| Luminous Efficacy | 100-150 lm/W (white), 40-80 lm/W (coloured) |
| Luminous Flux | 500-3000 lumens (depending on application) |
| Forward Current | 350mA to 1A (typical) |
| Forward Voltage | 3-4V per LED (white), 2-3V (coloured) |
| Junction Temperature | < 85°C (for long life) |
| Lifetime (L70) | 50,000 hours (at rated current) |
| Thermal Resistance | 2-5°C/W (junction to case) |
| Beam Pattern | Defined by secondary optics (reflector, lens, prism) |
| Protection Class | IP67 (when integrated in fixture) |
Electrical Requirements
| Requirement | Typical Value |
|---|---|
| Circuit Position | Downstream of LED driver, low-voltage DC load |
| Forward Current | 350mA to 1A (typical) |
| Forward Voltage | 3–4V per LED (white), 2–3V (coloured) |
| Isolation | Isolated from the primary series loop via the driver and transformer |
| Thermal Requirement | Requires adequate heat sinking to keep junction temperature < 85°C |
| Fault Protection | LED string failure is detected via driver output monitoring, not a series-loop fault |
Applicable Standards
ICAO Annex 14
Photometric and colour requirements for LED-based AGL lights
FAA AC 150/5345-46
Specification for LED AGL luminaires
IEC 61827
Electrical and photometric characteristics for AGL luminaires
IES LM-79 / LM-80
Photometric measurement and long-term lumen maintenance testing for LED light sources
Installation Requirements
Thermal Interface Application
MechanicalApply the thermal interface layer evenly to the MCPCB's rear face before bolting or clipping the module to the heat sink, eliminating air gaps that would raise thermal resistance.
Keyed Frame Alignment
MechanicalFit the module using the locating pins or keyed mounting frame so its rotational and lateral position is fixed relative to the downstream secondary optic.
Sealed Connector Termination
ElectricalConnect the module through its sealed, often locking, connector, confirming polarity before the driver circuit is energised.
Colour Bin Matching
MechanicalConfirm the module's colour and output bin matches the array's design specification, since binning consistency drives uniform chromaticity and intensity across the beam.
Pre-Energisation Sign-off
DocumentationRecord module positioning, connector confirmation, and colour bin details as-built before the circuit is energised for current and colour verification.
Testing & Commissioning
Driver Circuit Continuity Test
Pre-EnergisationConfirm continuity between the LED module and its driver, and check polarity, before the circuit is first energised.
Current Verification
EnergisationWith the CCR energised, confirm the module operates at its correct drive current at each commissioned intensity step.
Colour Consistency Check
EnergisationConfirm chromaticity is consistent across all modules in the array, flagging any module outside the accepted colour tolerance.
Photometric Commissioning Test
Final AcceptanceMeasure beam intensity and colour with a calibrated photometer against ICAO/FAA commissioning tolerances prior to handover.
Thermal Performance Check
Final AcceptanceAfter a burn-in period under sustained operation, confirm the module's case temperature stays within its specified limit.
Documentation & As-Built Sign-off
Final AcceptanceRecord current, colour, and photometric readings in the commissioning dossier for handover.
Inspection & Maintenance
Lumen Depreciation Check
AnnualMeasure light output against baseline to track lumen depreciation and plan replacement before it falls out of spec.
Thermal Pathway Inspection
AnnualCheck the thermal path from module to heat sink for degraded interface material or loose mounting.
Colour Consistency Check
AnnualVerify colour output hasn't shifted from the rated value, which can indicate uneven ageing across the LED array.
Driver Circuit Continuity Test
AnnualTest circuit continuity and connections between the module and its driver to catch developing faults early.
Common Field Issues
LED Degradation (Lumen Depreciation)
Over time, LED modules experience gradual lumen depreciation due to thermal stress and chip aging. Regular photometric measurements are essential to identify modules that have fallen below acceptable intensity levels.
Thermal Management Failure
If the heat sink or thermal interface becomes compromised (e.g., due to dust accumulation or loose mounting), LED junction temperature rises, accelerating degradation and reducing life. Regular inspection and cleaning of cooling paths is recommended.
Driver Circuit Failure
The constant-current driver is a common failure point. Surges, moisture ingress, or component aging can cause driver failure, leading to flickering or complete loss of light. Replace the module or driver as required.
Colour Shift
LED colour can shift over time due to phosphor degradation (in white LEDs) or changes in the semiconductor junction. Colour shift can affect compliance with ICAO chromaticity coordinates. Replace modules that show significant colour shift.
Troubleshooting Guide
Module Completely Dark
Flickering or Intermittent Output
Reduced Light Output
Colour Outside Chromaticity Tolerance
Failure Modes & Root Causes
Driver or Interconnect Failure
Driver Output Instability
Thermal-Path Degradation
Chromaticity Shift
Safety & Operational Notes
Electrical Isolation
Electrical SafetyLock out the fixture supply and verify zero energy before disconnecting or replacing the LED module; because the module is instant-on, treat the circuit as live the moment power is present rather than waiting to see if it lights.
ESD Precautions
Component HandlingUse anti-static precautions when handling the module's MCPCB and integrated drive circuitry to avoid latent damage that may not show up until later in service.
Direct Viewing
Personnel SafetyAvoid staring directly into the LED array during functional testing, particularly on high-intensity modules.
Thermal Contact on Reinstallation
MechanicalEnsure proper thermal contact with the heat sink when reseating a module; poor thermal coupling accelerates lumen depreciation and colour shift even if the module appears to work normally at first.
Correct Colour Replacement
ComplianceConfirm the replacement module is the correct colour and intensity variant for the fixture; modules across the white, green, red, yellow, and blue range can be physically similar but are not interchangeable.
PPE
Personnel SafetyUse insulated tools for electrical work and clean gloves when handling the module to avoid contaminating the optical surface.
Restore to Compliant State
ComplianceVerify colour, intensity, and beam pattern meet specification before closing out the work.
Engineering & Expert Notes
Lumen Depreciation Is Predictable, Not Random
PhotometricLED output declines on a fairly predictable curve driven by operating temperature and drive current, unlike a lamp filament's more abrupt end-of-life failure; use the manufacturer's L70/L80 depreciation data to plan proactive group replacement on high-value circuits rather than waiting for individual modules to fail a photometric spot check.
Thermal Coupling Failures Are Invisible at First Light
DiagnosticsA module reseated with poor thermal contact to its heat sink will still light correctly and pass an initial commissioning check; the accelerated depreciation and colour shift this causes only becomes apparent months later, so confirm proper thermal contact procedurally at reinstallation rather than relying on immediate visual performance.
Colour Binning Variation Between Batches Is Real
ProcurementLED modules from different production batches, even of the same nominal part number, can show a visible colour or intensity variation known as binning drift; when replacing a subset of modules on a shared circuit, source from a batch matched as closely as possible to the existing modules to avoid a visibly inconsistent installation.
ESD Damage Can Be Latent, Not Immediate
Component HandlingA module that suffers minor electrostatic discharge damage during handling can still function correctly at first power-on while carrying a weakened junction that fails prematurely months later; enforce anti-static handling discipline as a standing procedure, since the consequence of skipping it doesn't show up until well after the installation is complete.
Colour-Specific Modules Are a Common Stores Mix-Up
ComplianceModules for different colours in the same physical form factor are easy to mix up in a stores environment, especially where labelling is small or packaging looks similar; verify colour on the module label at the point of installation, not just at the point of stores issue, since a colour error installed at a critical position (e.g., a stop bar or runway guard light) is a compliance issue, not just an aesthetic one.
Track Module Age Alongside the Fixture's Age
MaintenanceWhere a fixture has had its module replaced partway through its service life, the module's own age clock is independent of the fixture's; keep a per-module install date in maintenance records so depreciation-based replacement planning uses the module's actual service time rather than the fixture's overall age.
Related Components
Frequently Asked Questions
Short answers about AGL LED modules: construction, colours, power, thermal management, standards and maintenance.
Q1What is an LED module in an AGL fixture?
An LED module is a complete solid-state light engine for AGL applications. It consists of one or more high-power LEDs on a metal-core printed circuit board (MCPCB), with drive circuitry, thermal management and optical alignment features. It is the standard light source for modern LED-based AGL fixtures.
Q2How does an LED module compare with a halogen lamp?
LED modules offer higher efficacy (typically 100 to 150 lm/W for white and 40 to 80 lm/W for coloured), a lifetime of up to 50,000 hours (L70 at rated current), instant restart and good colour stability. That means fewer failed lights and fewer maintenance visits across an airfield.
Q3What colours are AGL LED modules available in?
White (4000 K to 6500 K), green, red, yellow and blue. White or yellow modules are used for runway edge and centreline lights, green and red for threshold and end lights, and blue and green for taxiway lights. Specialised modules produce the red/white transition needed for PAPI and VASI.
Q4How is an LED module powered and dimmed?
It is powered from the series circuit through an isolating transformer and LED driver, with intensity controlled by the CCR's current steps. The module typically runs at a forward current of 350 mA to 1 A, with a forward voltage of 3 to 4 V per LED for white and 2 to 3 V for coloured.
Q5Where does the LED module sit electrically?
It is a low-voltage DC load downstream of the LED driver, isolated from the primary series loop through the driver and transformer. An LED string failure is detected through the driver's output monitoring rather than as a series-loop fault.
Q6Why is thermal management so important for an LED module?
Heat at the LED junction accelerates degradation. The module needs adequate heat sinking to keep junction temperature below 85°C, and typical junction-to-case thermal resistance is 2 to 5°C/W. A degraded thermal interface, dust build-up or loose mounting raises junction temperature and speeds up lumen depreciation.
Q7Which standards apply to AGL LED modules?
The main references are ICAO Annex 14 (photometric and colour requirements), FAA AC 150/5345-46 (LED AGL luminaire specification), IEC 61827 and IES LM-79/LM-80 (photometric measurement and long-term lumen maintenance). Always verify the current edition and your aerodrome's approved requirements.
Q8How often should an LED module be checked?
Typical practice is an annual lumen depreciation check against baseline, thermal pathway inspection, colour consistency check and driver circuit continuity test. Your airport's approved maintenance programme takes precedence.
Q9What are the common LED module problems?
The common issues are gradual lumen depreciation, thermal management failure, driver circuit failure (a common failure point, caused by surges, moisture or component ageing) and colour shift from phosphor degradation or junction changes, which can affect compliance with ICAO chromaticity requirements.
Q10What should I check when replacing an LED module?
Lock out the supply and verify zero energy, use anti-static precautions, and confirm the replacement is the correct colour and intensity variant for the fixture. Make sure thermal contact with the heat sink is good, and verify colour, intensity and beam pattern meet specification before returning the fixture to service.
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Please read before relying on any content on this page.
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- 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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