Reflector
The precision mirror that captures and redirects light from the source into a controlled beam. Using parabolic, ellipsoidal, or faceted geometries, reflectors maximise optical efficiency and ensure accurate photometric performance for runway, taxiway, and approach lighting.
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What Is It?
A Reflector is a critical optical component in AGL fixtures that captures light emitted from the source (LED or halogen lamp) and redirects it into a defined beam pattern. Unlike a lens which transmits light, a reflector works by reflection — using highly polished metallic surfaces or dielectric coatings to achieve near-total internal reflection with minimal absorption. Reflectors are designed with precise geometries — parabolic, ellipsoidal, or faceted — to produce the required beam spread, intensity distribution, and cut-off angles. They are typically made from aluminium with a protective anodized or dichroic coating, or from glass with a silver or aluminum reflective layer.
Purpose & Function
The reflector's purpose, like the prism's, is to convert light radiating in many directions from the source into the tightly defined beam pattern a fixture is certified to produce — but it does so by redirecting light through reflection rather than bending it through refraction, which makes it well suited to fixtures needing very narrow, long-throw beams (parabolic geometry) or wide, even coverage (faceted geometry). Its high-reflectivity coating exists to capture as much of the source's output as possible and put it where it is useful, rather than letting it scatter or be absorbed — a direct driver of how efficiently the fixture converts electrical power into the intensity a pilot actually sees at range. Because beam shape is what allows a pilot to judge distance, alignment, or approach angle from the fixture's characteristic light pattern, the reflector's geometry is engineered as precisely as any other safety-critical optical component in the fixture.
Where Is It Used?
Reflectors are used in a wide range of AGL fixtures where precise beam control is required:
- Runway Edge & Centreline Lights: Parabolic reflectors for narrow, long-range beams.
- Threshold & End Lights: Ellipsoidal reflectors to project a uni-directional beam.
- Taxiway Lights: Faceted reflectors for wide, uniform illumination.
- Approach Lighting: High-efficiency reflectors for barrettes and crossbars.
- PAPI & VASI: Specialised reflectors that create the red/white colour transition.
- Obstruction Lights: Omnidirectional reflectors for 360° coverage.
Installation & Location
The reflector is fitted behind and around the lamp or LED module, secured to the housing so the light source sits precisely at (or very near) the reflector's focal point; a source mounted even a few millimetres off-focus will produce a beam that's wider, narrower, or misaimed compared to the fixture's rated photometrics. It's held in place by locating tabs, a bracket, or the lamp holder assembly itself, and its reflective surface is protected from scratching or fingerprints during fitting, since surface damage scatters light and reduces beam intensity. Once seated, it's enclosed behind the lens and top cover, and its position is checked whenever the lamp, LED module, or holder is serviced, since disturbing any of those parts can shift the reflector's alignment relative to the source.
How Does It Work?
A reflector works by reflecting light from the source according to the laws of reflection. The geometry of the reflector surface determines the beam shape:
- Parabolic: Reflects rays parallel to the axis, producing a narrow, collimated beam ideal for long-range illumination.
- Ellipsoidal: Focuses light to a second focal point, allowing control over beam divergence.
- Faceted: Uses multiple flat or curved segments to create a specific beam pattern, often used for wide distribution.
The reflective surface is coated with a highly reflective material — typically aluminium, silver, or a dielectric stack — to achieve reflectivity >95%. The reflector is designed to minimise light loss due to absorption and scattering, ensuring maximum photometric efficiency.
Reflector Geometry vs. Beam Shape & Control Logic
Light Source (LED or Halogen)
Emits in most directions before striking the reflective surface
Reflective Surface (>95% Reflectivity)
Aluminium, silver, or dielectric coating minimises absorption and scattering
Rays Reflected Parallel to Axis
Narrow, collimated beam
Long-Range Illumination
Focused to a Second Focal Point
Controlled beam divergence
Tunable Focus Distance
Multiple Flat or Curved Segments
Each facet aims at a different part of the field
Wide Beam Distribution
Reflector Geometry, Not Fixture Wattage, Is What Ultimately Shapes the Beam Pattern
Physical Construction
Metal reflectors are typically spun, stamped, or die-formed from aluminium sheet into the required parabolic, ellipsoidal, or faceted profile, then polished and finished with a vacuum-deposited or anodised reflective layer to maximise reflectivity while resisting oxidation. Glass reflectors instead start as a moulded or ground glass substrate onto which a silver or aluminium reflective layer is deposited and protected by a back coating, offering higher reflectivity at the cost of greater fragility and weight. In either case, the reflector's exact geometry is held to close manufacturing tolerance, since the surface shape — not just its reflectivity — is what concentrates the light source's output into the required beam spread and cut-off angle. The finished reflector seats in the housing on locating features that fix it precisely around the light source, typically retained by clips, screws, or a bonded joint, so its optical axis stays aligned with the lamp or LED module through vibration and thermal cycling in service.
Technical Parameters
| Parameter | Typical Value |
|---|---|
| Material | Aluminium (anodized), glass with silver/aluminium coating, or plastic with dielectric coating |
| Reflectivity | >95% (visible spectrum) |
| Geometry | Parabolic, ellipsoidal, faceted, or free-form |
| Surface Finish | Optical polish (Ra < 0.05 µm) |
| Coating | Anodized, dichroic, or silver with protective overcoat |
| Temperature Range | -40°C to +150°C (for high-temperature lamps) |
| UV Resistance | UV-stabilised coatings |
| Beam Angle (Typical) | 2° to 12° (depending on application) |
Applicable Standards
ICAO Annex 14
Photometric requirements for AGL reflectors
FAA AC 150/5345-46
Specification for AGL fixture optics
FAA EB 67
Engineering Brief: Light Sources Other Than Incandescent and Xenon — governs LED retrofit optics, including reflector-based LED fixture qualification
IEC TS 61827
Characteristics of inset and elevated luminaires used on aerodromes and heliports — the fixture-level photometric performance a reflector is designed to deliver
Note on figures: the values on this page are typical reference figures drawn from the standards listed above and from manufacturers’ published data. Always design, install, commission and maintain to the project specification, the manufacturer’s manual and the standard in force at the aerodrome.
Installation Requirements
Surface Handling
Pre-FitProtect the reflective surface from scratching or fingerprints during handling and fitting, since any surface damage scatters light and reduces beam intensity.
Focal Point Positioning
FitSecure the reflector so the lamp or LED module sits precisely at, or very near, the reflector's focal point, since a source mounted even a few millimetres off-focus widens, narrows, or misaims the beam.
Locating Tab / Bracket Engagement
FitConfirm the reflector is fully engaged on its locating tabs, bracket, or lamp holder assembly before closing the fixture, so its optical axis stays fixed relative to the source.
Position Recheck on Servicing
FitRecheck reflector position whenever the lamp, LED module, or holder is serviced, since disturbing any of those parts can shift the reflector's alignment.
Enclosure Confirmation
Post-FitConfirm the reflector is fully enclosed behind the lens and top cover with no gaps before the fixture is returned to service.
Pre-Energisation Sign-off
DocumentationRecord reflector condition and seating before the fixture is closed up, since alignment is not inspectable once assembly is complete.
Testing & Commissioning
Reflectivity Verification
Pre-InstallationConfirm reflectivity meets specification using a reflectometer or reference sample before the reflector is fitted.
Surface Condition Check
Pre-InstallationInspect the reflective coating for scratches, corrosion, or handling damage before installation.
Alignment Verification
InstallationConfirm the reflector's geometric axis is correctly aligned with the light source and the fixture's optical centreline.
Photometric Commissioning Test
Final AcceptanceMeasure beam intensity and pattern with a calibrated photometer against ICAO/FAA commissioning tolerances.
Documentation & As-Built Sign-off
Final AcceptanceRecord alignment and photometric test results in the commissioning dossier for handover.
Inspection & Maintenance
Reflectivity Check
AnnualMeasure reflectivity against baseline, since gradual degradation can quietly reduce beam intensity.
Surface & Corrosion Inspection
AnnualCheck aluminium reflector surfaces for pitting or corrosion that scatters or absorbs light.
Alignment Verification
Semi-annualConfirm reflector alignment hasn't shifted during other servicing, which can distort the beam pattern.
Cleaning
QuarterlyClean the reflector surface of dust and residue to maintain maximum reflected output.
Common Field Issues
Reflectivity Degradation
Over time, the reflective coating can oxidise, tarnish, or become contaminated with dust and pollutants, reducing reflectivity and light output. Regular cleaning and periodic replacement are recommended.
Thermal Stress Cracking
Glass reflectors can crack due to thermal shock from rapid temperature changes. Use of borosilicate glass or proper thermal management in the fixture design is essential.
Misalignment During Maintenance
If the reflector is disturbed or removed during lamp replacement, the beam pattern can be misaligned. Always use alignment jigs and follow manufacturer's specifications to restore the correct optical orientation.
Corrosion of Aluminium Reflectors
In coastal or high-humidity environments, aluminium reflectors can corrode, especially if the anodized coating is damaged. Use of marine-grade anodizing or stainless steel alternatives is recommended.
Troubleshooting Guide
Reduced Light Output
Cracked Glass Reflector
Beam Pattern Off-Aim After Maintenance
Visible Pitting or White Corrosion on an Aluminium Reflector
Failure Modes & Root Causes
Coating Oxidation / Contamination
Thermal-Shock Cracking
Misorientation After Service
Pitting / Galvanic Corrosion
Safety & Operational Notes
De-Energise Before Removal
Electrical SafetyIsolate the fixture and allow the lamp to cool before removing the reflector; a live circuit or hot lamp behind the optic is a shock and burn hazard during service.
Preserve Orientation on Reinstall
WorkmanshipNote the reflector's orientation markings before removal and reinstall it exactly as found; a misoriented reflector throws the beam off-aim even though the optic itself is undamaged.
Thermal Shock Avoidance
HandlingDo not apply a cold cleaning solution to a hot reflector or reinstall immediately after a lamp change; allow the fixture to reach ambient temperature to avoid thermal-shock cracking on glass units.
Coating-Safe Cleaning
WorkmanshipClean the reflective surface with a soft cloth and manufacturer-approved cleaner rather than an abrasive pad; scratching or wearing through the anodized coating exposes bare aluminium to pitting corrosion, which is irreversible.
FOD Control
OperationalAccount for the removed reflector, gasket, and fasteners at all times during handling, and secure or remove any loose material before returning the fixture to service to prevent foreign object debris on the movement area.
Verify Beam Aim After Service
ComplianceCheck beam aim against the alignment jig or reference orientation after any reflector work before closing out the task, since orientation errors are not visually obvious.
Restore to Compliant State
ComplianceDo not return a fixture to service with a cracked, pitted, or misoriented reflector; confirm the optic is fully seated and correctly aligned before closing out the work.
Engineering & Expert Notes
Orientation Marks Wear Off Before the Reflector Does
WorkmanshipA factory orientation mark on a reflector can fade or rub off well before the optic itself needs replacement; re-mark the orientation in a durable way at every service if the original marking is hard to read, rather than guessing from memory.
Rapid Cooling Cracks Glass Reflectors the Same Way Rapid Heating Does
HandlingA hot glass reflector exposed to cold night air or a draft during changeover can crack from rapid cooling just as readily as from a cold cleaner applied to a hot unit; let ambient conditions equalize from both directions, not just after removing a heat source.
A Dimming Beam Can Be Coating Pitting, Not Lamp Aging
TroubleshootingA gradually dimming or scattered beam is often assumed to be lamp aging first; check for anodized coating pitting or corrosion on the reflective surface before replacing the light source, since a degraded reflector produces the same symptom.
Verify Beam Aim With an Instrument, Not by Eye
ComplianceOrientation and aim errors from reflector work are not reliably detectable by eye, especially at night; use an alignment jig or photometric check after any reflector service rather than judging the beam visually.
Gasket Compression Set Outlasts the Reflector's Visual Condition
DurabilityA reflector gasket can lose sealing force well before the reflector itself shows any wear, so an optic that looks fine on removal doesn't mean its gasket is still doing its job; replace the gasket at every reflector service as routine.
A Single Fingerprint Can Start Irreversible Pitting
HandlingOils from bare-hand handling on an anodized reflective surface can create a localized weak point in the coating that accelerates corrosion under humidity cycling, even after the fingerprint itself is cleaned off; handle reflectors by the edges or mounting tabs from the first touch.
Frequently Asked Questions
Short answers about the reflector: what it is, how it works, specifications, standards, maintenance and common faults.
Q1What is a reflector in an AGL fixture?
A reflector is an optical component that captures light from the source (LED or halogen lamp) and redirects it into a defined beam pattern by reflection, using highly polished metallic surfaces or dielectric coatings. Geometry sets the beam spread, intensity distribution and cut-off angles.
Q2What types of reflector geometry are used?
Parabolic reflectors produce a narrow, collimated beam for long range. Ellipsoidal reflectors focus light to a second focal point to control beam divergence. Faceted reflectors use multiple flat or curved segments for a specific pattern, often a wide distribution.
Q3How reflective is an AGL reflector?
Reflectivity is typically above 95% in the visible spectrum. Surfaces are optically polished (Ra below 0.05 µm) and coated with anodising, a dichroic stack, or silver with a protective overcoat.
Q4What materials and temperatures are involved?
Typical materials are anodised aluminium, glass with a silver or aluminium coating, or plastic with a dielectric coating. The temperature range is -40°C to +150°C for high-temperature lamps, with UV-stabilised coatings.
Q5Where are reflectors used?
In runway edge and centreline lights (parabolic), threshold and end lights (ellipsoidal), taxiway lights (faceted), approach lighting barrettes and crossbars, and PAPI and VASI units.
Q6What is the difference between a reflector and a lens?
A lens transmits light, while a reflector works by reflection from a polished or coated surface, minimising absorption. Typical reflector beam angles are 2° to 12° depending on the application.
Q7Which standards apply to reflectors?
The main references are ICAO Annex 14, FAA AC 150/5345-46, FAA Engineering Brief 67 (light sources other than incandescent and xenon, covering LED retrofit optics) and IEC TS 61827. Always verify the current edition and your aerodrome's approved requirements.
Q8How often should a reflector be maintained?
Typical intervals are quarterly for cleaning, semi-annual for alignment verification, and annual for reflectivity checks and surface and corrosion inspection. Your airport's approved maintenance programme takes precedence.
Q9What are the common problems with reflectors?
Common problems are reflectivity degradation from coating oxidation or contamination, thermal stress cracking of glass reflectors, misalignment during maintenance, and pitting or white corrosion on aluminium reflectors. Reduced light output is the typical symptom.
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