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Safety-critical technical reference — read before use. Independent educational guidance for qualified AGL and aerodrome personnel. It is not an approved procedure, design, specification or regulatory instruction and does not replace your aerodrome’s permit-to-work, isolation/LOTO procedures, the approved design or the manufacturer’s instructions. Series-circuit AGL equipment can carry lethal voltages. Read the full disclaimer ↓
THE AGL ENGINEERING CENTRE by Precision AGL Academy · Taxiway Photometry

Taxiway Lighting Photometry & Intensity Testing

How photometry verifies the intensity, distribution, colour and alignment of taxiway edge, centreline, stop bar and runway guard lights. A taxiway light can stay illuminated while giving too little output or pointing its beam the wrong way.

Start Learning AGL Photometry Concepts
Overview

What Is Taxiway Lighting Photometry?

Taxiway lighting photometry is the quantitative evaluation of the optical output of taxiway lighting fixtures. It verifies that installed lights give the required intensity, distribution, colour and alignment for their operational function, as visual guidance for aircraft moving between runways, aprons, terminals and other manoeuvring areas.

More than electricity reaching the fixture

The objective is to decide whether the light works as an optical guidance device. A fixture can remain illuminated while giving inadequate intensity or an incorrectly directed beam.

Function drives the method

An elevated edge light and an in-pavement centreline light may share a series circuit, yet their optical geometry and measurement requirements differ substantially. Base the method on the fixture's function, not its appearance.

Testing may evaluate

Luminous intensityIntensity distributionBeam coverageColourAlignmentOptical consistencyFixture-to-fixture performanceDegradation from baseline

Taxiway photometry is performed during

CommissioningRehabilitationAcceptance testingPeriodic maintenanceAfter fixture replacementAfter pavement or civil worksTroubleshootingPerformance investigationsAuthority or airport inspections
Match the procedure to the light type, the applicable airport lighting standard, the project specification and the equipment documentation.

Related Guides

AGL photometry concepts Runway lighting photometry Taxiway lighting systems
Interactive

What to Test on Each Taxiway Light Type

Pick a light type to see what the test should cover. This is a planning aid; the approved specification sets the parameters and limits.

Test should consider

    Watch for

      Fixture Types

      Edge, Centreline, Stop Bar and Guard Light Comparison

      Lighting typeTypical installationMain photometric considerations
      Taxiway edgeElevated or in-pavementIntensity, colour, alignment, coverage
      Taxiway centrelineUsually in-pavementIntensity, distribution, colour, alignment
      Stop barIn-pavementIntensity, colour, consistency, orientation
      Runway guard lightElevated or in-pavement, by configurationIntensity, colour, directional performance
      A functional overview, not a substitute for the applicable design or regulatory requirements. A photometric programme may also cover intersection lighting and other specialized taxiway visual aids where applicable.

      Related Guides

      Runway guard lights and stop bars Runway incursion prevention and SMGCS Taxiway lighting systems
      Measurement

      Intensity, Distribution and Colour

      Intensity

      Varies with fixture type, optical design, light source, operating step, viewing angle, measurement geometry, electrical condition and fixture condition. Tie every result to its operating condition.

      Distribution

      A fixture can be strong at one angle and weak elsewhere in its required coverage. Peak intensity alone does not describe performance.

      Colour

      A fixture can look bright yet have colour outside requirement. Verify colour separately from intensity where required.

      How Is Taxiway Light Intensity Measured?

      Taxiway light intensity is measured with calibrated photometric equipment in a controlled geometry. The fixture is inspected and, where required, cleaned first. The operating condition is set and recorded, and the sensor position and fixture orientation are established. The measurement is then compared with the applicable requirement or with earlier test data. See the measurement procedure below for the full sequence.

      Taxiway Light Intensity Measurement: Why Operating Step Matters

      Where the system has several brightness settings, a fixture measured at one cannot be compared with a criterion for another. Record the intensity step, control-system condition, fixture type, test position and measurement geometry.

      Colour degradation

      Causes include light-source degradation, filter condition, optical components, lens contamination, incorrect replacement parts and ageing optics.

      Distribution parameters

      ParameterWhat it shows
      Peak intensityHighest measured intensity in the relevant measurement area
      Angular distributionHow output changes with viewing angle
      Beam coverageWhether output is sufficient over the required angular region
      DirectionalityWhether light goes toward the intended operational area
      UniformityWhether adjacent fixtures give a consistent visual pattern
      Take colour and intensity limits from the governing aerodrome standard or approved fixture specification, not from a generic value, including any on this site.

      Taxiway beam: bright core and dimmer fan.

      TAXIWAY / OPTICAL BEAM SIDE VIEW · EDGE LIGHT 30° 6° 0° 6°–30° AT LEAST 0.2 cd 0°–6° AT LEAST 2 cd · BRIGHT CORE A PILOT TAXIING TOWARD THE LIGHT SEES IT AT A LOW ANGLE, INSIDE THE BRIGHT CORE PLAN VIEW · AZIMUTH AIRCRAFT BESIDE THE TAXIWAY DOES NOT SEE THIS CENTRELINE LIGHT CENTRELINE BEAM IS NARROW SEEN ALONG THE TAXIWAY, BOTH WAYS EDGE LIGHT: WIDE AZIMUTH, SEEN FROM EITHER DIRECTION STRAIGHT SECTION SHOWNCURVES USE A WIDER CENTRELINE BEAM SCHEMATIC VIEW · BEAM ANGLES AND LOBE SHAPES ILLUSTRATIVE · NOT TO SCALE
      Figure 1. Taxiway light beam shown as a side view and a plan view. Peak intensity alone does not describe performance.
      AGL Visual Encyclopedia: Taxiway optical beam Photometric distribution Isocandela diagram

      Where each AGL colour is used.

      WHAT EACH COLOUR MEANS, AND WHERE YOU SEE IT PLAN VIEW · LANDING LEFT TO RIGHT · ILLUSTRATIVE, NOT TO SCALE PAPI: WHITE ABOVE · RED BELOW OBSTACLE LIGHT: RED BEACON: WHITE / GREEN RUNWAY EDGE: WHITE CAUTION ZONE: YELLOW RUNWAY END: RED APPROACH LIGHTS: WHITE SIDE ROWS: RED (CAT II/III) CENTRELINE: WHITE → RED/WHITE → RED TOUCHDOWN ZONE: WHITE THRESHOLD + WING BARS: GREEN GUARD LIGHTS: YELLOW TAXIWAY EDGE: BLUE RUNWAY-SIDE CENTRELINE: GREEN / YELLOW STOP BAR: RED TAXIWAY CENTRELINE: GREEN WHITE THE RUNWAY ITSELF RUNWAY EDGE CENTRELINE TOUCHDOWN ZONE APPROACH · PAPI YELLOW CAUTION EDGE, FINAL ZONE GUARD LIGHTS INTERMEDIATE HOLDING ILS-AREA CENTRELINE GREEN GO · SAFE PATH RUNWAY THRESHOLD THRESHOLD WING BARS TAXIWAY CENTRELINE LEAD-ON LIGHTS RED STOP · DANGER RUNWAY END STOP BARS CENTRELINE LAST ZONE OBSTACLES · PAPI LOW BLUE TAXIWAY EDGE TAXIWAY EDGE LIGHTS NEVER ON A RUNWAY OMNIDIRECTIONAL WHITE = RUNWAY · YELLOW = CAUTION · GREEN = GO · RED = STOP · BLUE = TAXIWAY EDGE
      Figure 2. AGL colour code summary. Verify colour separately from intensity where required.
      AGL Visual Encyclopedia: AGL colour code summary Colour coordinates Colour measurement
      Equipment

      Taxiway Photometer Setup, Calibration and Positioning

      Equipment

      Photometric sensor, optical sensor, positioning equipment, angular and distance measurement, data acquisition unit, measurement software, location or mapping system and calibration references. The configuration depends on the test system.

      Before testing, verify and record

      • Instrument identification, model and serial number
      • Calibration status and certificate
      • Sensor condition
      • Software configuration and measurement range
      • Data acquisition settings

      Calibration is not enough

      A calibrated instrument does not guarantee a valid measurement. The complete test arrangement must also be correct.

      Positioning

      Accuracy depends on horizontal and vertical position, distance, viewing angle, sensor orientation and fixture orientation. A small error can change measured intensity, especially for directional fixtures.

      Current measurement
      Previous measurement
      Baseline measurement
      Keep the same geometry for repeat tests. Without it, an apparent change in performance may only be a change in test set-up.

      Related Guides

      AGL photometric testing guide Component library

      Fixture on a rotating stage, photometer at a measured distance.

      PHOTOMETER ARRANGEMENT · SIDE VIEW · SCHEMATICDARK ROOMBAFFLESdTEST DISTANCEFIXTURE ROTATES · PHOTOMETER STAYS FIXED123451FIXTURE ON STAGERotates to each test angle2BEAM AXISAimed at the photometer3TEST DISTANCELong enough for a point source4PHOTOMETERFixed detector reads the light5STRAY LIGHT CONTROLDark room and bafflesSCHEMATIC · PROPORTIONS ARE ILLUSTRATIVE, NOT A TEST SETUP DRAWING
      Figure 3. Photometer arrangement in a dark room with baffles. A calibrated instrument does not guarantee a valid measurement.
      AGL Visual Encyclopedia: Photometer arrangement Photometric testing arrangement Measurement points
      An airman measuring the distance between two airfield lights with a measuring wheel
      Photo 1. An airman measures the distance between two airfield lights with a measuring wheel. Repeat photometric tests need the same measurement geometry.Credit: U.S. Air Force photo by Airman 1st Class Austin Mayfield, Dyess Air Force Base, Jan. 12, 2016. Public domain (US Government work). Source page
      Procedure

      Taxiway Photometry Measurement Procedure

      A controlled taxiway test follows twelve steps.

      01

      Review requirements

      Taxiway designation, lighting configuration, fixture types, scope, authority requirements, specifications, equipment requirements and required operating conditions.

      02

      Review drawings

      Lighting layout, fixture schedule and locations, cable circuit information, datasheets, previous test data and as-builts.

      03

      Verify photometric equipment

      Calibration, instrument configuration, sensor condition, data system, positioning system and software.

      04

      Inspect the lighting

      Dirty or damaged lenses, broken housings, water ingress, loose fixtures, wrong orientation, missing components, damaged cables or connectors.

      05

      Clean and prepare fixtures

      Where required, clean optical surfaces before the final acceptance measurement so contamination is not read as permanent degradation.

      06

      Confirm the operating condition

      Set the required intensity or operating mode and record it.

      07

      Establish measurement geometry

      Position the photometer per the test procedure: distance, height, orientation, angle and reference direction.

      08

      Measure the fixture

      Record fixture ID, location, type, operating step and photometric data.

      09

      Analyse the results

      Compare with the applicable acceptance criteria.

      10

      Investigate failures

      Contamination, alignment, optics, light source, electrical supply or measurement error.

      11

      Correct the defect

      Complete the required maintenance or adjustment.

      12

      Retest

      Repeat the measurement and document the final result.

      The measurement procedure at a glance.

      PHOTOMETRIC TESTING PROCESS · SEVEN STEPS, FROM MOUNTING TO REPORT 1 PREPARE Identify & mount 2 ALIGN Axis & centre 3 STABILISE Rated current 4 SCAN Grid, angle by angle 5 CHECK Repeat reference 6 RECORD Data table 7 REPORT Isocandela & report STEP 4 · SCANNING THE MEASUREMENT GRID · ONE READING PER GRID POINT HORIZONTAL ANGLE → VERTICAL ANGLE → INTENSITY TABLE H 0 / V 0 1850 cd H 2 / V 0 1420 cd H 0 / V 2 1610 cd H 2 / V 2 1180 cd EXAMPLE VALUES ONLY ISOCANDELA DIAGRAM & PHOTOMETRIC REPORT REPEAT A REFERENCE READING DURING AND AFTER THE SCAN DRIFT FOUND → REPEAT THAT PART, DO NOT REPORT IT RING = FINER SPACING NEAR THE PEAK COLOUR ALSO MEASURED FOR COLOURED LIGHTS SCHEMATIC · EXAMPLE VALUES ONLY · LIMITS FOLLOW THE STANDARD AND LABORATORY PROCEDURE
      Figure 4. Simplified photometric testing process. The twelve numbered steps on this page give the full sequence.
      AGL Visual Encyclopedia: Photometric testing process Photometric grid Light intensity measurement
      Alignment

      Taxiway Lighting Alignment

      Why it matters

      A light with good optical output still fails to guide if its beam points the wrong way. Photometry can reveal an error when the measured beam is displaced from its intended measurement region.

      Alignment errors come from

      • Accidental impact
      • Maintenance work or fixture replacement
      • Mounting movement and loose hardware
      • Foundation problems
      • Incorrect initial installation
      • Pavement works

      Troubleshooting sequence

      Abnormal measurement
      Verify photometer set-up
      Verify operating step
      Inspect fixture
      Clean optical surface
      Check physical alignment
      Inspect optics
      Check electrical condition
      Correct defect
      Retest
      This approach reduces unnecessary fixture replacement.

      Why alignment changes the measured peak.

      FIXTURE ALIGNMENT · GONIOMETER SIDE VIEW · ALIGNED VS MISALIGNED ALIGNED ROTATION AXIS PHOTOMETER REFERENCE AXIS ON PHOTOMETER LINE LIGHT CENTRE ON AXIS · ZERO ANGLES TRUE PEAK READS AT THE DESIGNED ANGLE MISALIGNED ROTATION AXIS PHOTOMETER MISSES AXIS ROTATED · LIGHT CENTRE OFF AXIS WHOLE PATTERN SHIFTED OR ROTATED PEAK AT THE WRONG ANGLE · POINT VALUES WRONG 1 MOUNT On the reference surface 2 CENTRE Light centre on the axis 3 AIM Axis at the photometer 4 ZERO Set the zero angles 5 RECORD Lock it, then measure SCHEMATIC · ANGLES EXAGGERATED · METHOD AND TOLERANCES FOLLOW THE TEST LABORATORY’S PROCEDURE
      Figure 5. Aligned and misaligned fixture on a photometric goniometer. Keep the same geometry for repeat tests.
      AGL Visual Encyclopedia: Fixture alignment in photometry Taxiway fixture orientation Alignment verification
      An airman checking the alignment of an airfield lighting system
      Photo 2. An airman checks the alignment of an airfield lighting system. Alignment affects the measured beam, so verify it before photometry.Credit: U.S. Air Force photo by Senior Airman Jasmyne Bridgers-Matos, Tyndall Air Force Base, Jan. 26, 2025. Public domain (US Government work). Source page
      Troubleshooting

      Common Taxiway Lighting Failures

      Click a failure to see the causes to investigate.

      Low intensity

      Possible Cause

      • Degraded lamp or LED
      • Dirty optical surfaces
      • Damaged lens
      • Ageing optics
      • Incorrect light source
      • Electrical problems
      • Incorrect intensity setting

      Beam misalignment

      Possible Cause

      • Impact damage
      • Loose mounting
      • Incorrect installation
      • Fixture replacement
      • Mechanical movement
      • Maintenance error

      Colour deviation

      Possible Cause

      • Degraded optical components
      • Incorrect lamp or LED assembly
      • Damaged filter
      • Contamination
      • Incorrect replacement component

      Water ingress

      Possible Cause

      • Condensation
      • Corrosion
      • Optical degradation
      • Electrical faults
      • Reduced transmission through the optical window

      In-pavement contamination

      Possible Cause

      • Rubber deposits
      • Dust and dirt
      • Pavement debris
      • Fluid contamination

      Electrical causes

      Not every poor result is optical. Look at abnormal series-circuit current, isolation transformer problems, damaged connectors, cable faults, poor connections, incorrect regulator settings and secondary-side wiring problems.

      Several lights at once

      When several taxiway lights perform abnormally together, investigate the common electrical supply before treating each as an independent failure.

      CCR
      Primary series circuit cable
      Isolation transformer
      Secondary connector
      Taxiway light
      Optical output

      Related Guides

      Troubleshooting Engine CCR working principle Airport isolating transformer Junction boxes and housings

      Four common photometric failures as contours.

      PHOTOMETRIC FAILURE · REQUIRED AREA DRAWN OVER THE MEASURED CONTOURS 1 TOO DIM CONTOURS SHRINK Required box not reached Dirty lens · ageing · low current 2 BEAM SHIFTED CONTOURS OFF TARGET Peak outside the box Mis-aimed · off reference axis 3 BEAM TOO NARROW CONTOURS STRETCHED Box sides uncovered Wrong or damaged optic 4 COLOUR FAILURE CHROMATICITY (x, y) COLOUR LIMITS MEASURED INTENSITY MAY BE FINE Colour point outside its box Faded filter · wrong source 1 OVERLAY Requirement on the diagram 2 FIND What is uncovered or out of limit 3 TRACE Shape points to the cause FIXTURE OR TEST? CHECK ALIGNMENT AND SET-UP BEFORE CONDEMNING THE FIXTURE SCHEMATIC · SHAPES ARE ILLUSTRATIVE · REQUIRED AREAS AND LIMITS COME FROM THE APPLICABLE STANDARD
      Figure 6. Too dim, off-axis, wrong shape and wrong colour, each shown against the required area.
      AGL Visual Encyclopedia: Photometric failure visualization Misalignment LED failure
      Staged Approach

      Structured Troubleshooting of an Abnormal Result

      Stage 1: Verify the measurement

      Photometer calibration, sensor position, geometry, fixture ID, operating intensity and repeatability.

      Stage 2: Inspect the fixture

      Lens, optics, housing, orientation, contamination, water ingress and mechanical damage.

      Stage 3: Check the electrical system

      Supply condition, series-circuit operation, isolation transformer, connectors, wiring and control system.

      Stage 4: Correct the defect

      Clean, align, repair or replace as appropriate.

      Stage 5: Retest

      Confirm the final photometric result.

      Cleaning first: use measure, clean, re-measure rather than measure, replace. Record whether output improved after cleaning, which separates contamination from true optical or electrical degradation.

      Acceptance

      Acceptance Testing, Baseline Data and Reports

      New installations

      Build photometry into commissioning rather than leaving it to periodic maintenance. The first results become the baseline performance of the installation.

      Rehabilitation

      After major rehabilitation, compare previous and new data to find improvements or remaining deficiencies.

      Baseline record, per fixture

      • Fixture ID, exact location and type
      • Operating condition
      • Measured intensity and relevant optical parameters
      • Alignment information and colour result where measured
      • Date and instrument details
      Baseline
      Year 1
      Year 2
      Year 3
      A trend like this reveals gradual degradation that a single pass/fail check would miss.

      Example report table

      Fixture IDTaxiwayFixture typeOperating stepMeasured resultAcceptance criterionStatus
      TW-01Taxiway AEdge lightSpecified stepRecorded valueApplicable limitPass
      TW-02Taxiway AEdge lightSpecified stepRecorded valueApplicable limitPass
      TW-CN-01Taxiway ACentrelineSpecified stepRecorded valueApplicable limitInvestigate
      SB-01Holding positionStop barSpecified stepRecorded valueApplicable limitPass
      Take acceptance values from the applicable controlled specification.

      Project and equipment

      Airport, taxiway, project number, date, organisation, personnel; photometer manufacturer, model, serial, calibration status and certificate, software version.

      Fixture information

      Fixture ID, type, manufacturer, model, location, installation type and operating intensity.

      What the report must prove

      What was tested, with what equipment, under what conditions, what was measured, what the requirement was, and what happened to failed units.

      Reading a photometric report in six steps.

      PHOTOMETRIC REPORT · SIX THINGS TO READ, IN ORDER 1 IDENTIFY What was tested 2 CONDITIONS Current, distance 3 DATA Table & isocandela 4 COMPARE Against requirement 5 COLOUR Chromaticity 6 CONCLUDE Result & limits EXAMPLE REPORT SHEET · READ AGAINST THE REQUIREMENT, NOT ON ITS OWN 1 FIXTURE · SOURCE · COLOUR · LABORATORY · DATE 2 RATED CURRENT · TEST DISTANCE · STANDARD USED 3 ISOCANDELA DIAGRAM · DASHED BOX = REQUIRED AREA 5 CHROMATICITY x, y inside the colour limits 4 POINT-BY-POINT COMPARISON POINT REQUIRED MIN MEASURED RESULT A (0, 0) 1500 cd 1850 cd PASS B (+2, 0) 1000 cd 1120 cd PASS C (-2, 0) 1000 cd 960 cd FAIL D (0, +1) 800 cd 880 cd PASS ONE POINT BELOW ITS LIMIT IS A FAILURE · EXAMPLE VALUES ONLY 6 RESULT APPLIES TO THE TESTED SAMPLE UNDER STATED CONDITIONS SCHEMATIC · EXAMPLE VALUES ONLY · REQUIRED POINTS AND LIMITS COME FROM THE APPLICABLE STANDARD
      Figure 7. Photometric report interpretation. Take acceptance values from the governing specification.
      AGL Visual Encyclopedia: Report interpretation Data interpretation Before and after photometry
      Maintenance

      Maintenance, Replacement and Pavement Work

      Maintenance testing

      Test periodically, after major maintenance, replacement, accidental impact or resurfacing, when pilots report abnormal lighting, when visual inspection finds inconsistent output, or as part of an asset-condition programme.

      Classify results

      Normal, monitor, maintenance required, failed or retest required. This is more useful than recording only ON or OFF.

      After fixture replacement, verify

      • Correct fixture type and optical assembly
      • Installation orientation and mechanical position
      • Electrical connection and operating condition
      • Photometric output, especially when changing technology or optical design

      After pavement work, ask

      • Is the fixture correctly positioned?
      • Is the optical system undamaged?
      • Is the beam correctly aligned?
      • Is the intensity acceptable, and the colour correct?
      • Does the overall lighting pattern remain consistent?
      Pavement work includes resurfacing, milling, repairs, fixture removal and reinstallation, drainage works, civil construction and taxiway geometry changes. Do not check only whether fixtures illuminate.

      Cleaning and photometric performance

      Cleaning matters most for fixtures at pavement level, where a contaminated optical surface cuts the light transmitted through the lens. Use the sequence below rather than replacing a fixture straight away, so contamination is separated from true optical or electrical degradation.

      Measure
      Clean
      Re-measure
      Instead of Measure, then Replace fixture. In maintenance reports, document whether output improved after cleaning.

      A three-level maintenance programme

      LevelActivityCovers
      1: Routine visual inspectionIdentify obvious defectsFailed lights, damaged fixtures, contamination, water ingress, physical movement
      2: Photometric inspectionMeasure optical performanceIntensity, distribution, colour, alignment, relevant optical parameters
      3: Detailed troubleshootingInvestigate the systemElectrical supply, CCR, transformer, connectors, cables, control system

      Related Guides

      AGL testing and inspection Maintenance handbook

      Same fixture before and after cleaning or repair.

      BEFORE AND AFTER · SAME FIXTURE, SAME SET-UP, SAME REQUIRED AREA 1 BEFORE PEAK AND CONTOURS TOO SMALL Required area not covered 2 AFTER CONTOURS COVER THE AREA Improvement to be checked against the limits ACTION TAKEN CLEAN · RE-AIM · REPLACE same set-up same grid and current 1 SAME SET-UP Same distance, grid and aiming reference both times 2 SAME CONDITIONS Same current step, warm-up and calibrated photometer 3 SAME REQUIREMENT Overlay the same required area on both results IF THE SET-UP CHANGES, THE COMPARISON NO LONGER SHOWS THE FIXTURE SCHEMATIC · ILLUSTRATIVE SHAPES, NOT MEASURED DATA
      Figure 8. Before and after photometry of one fixture. Do not check only whether fixtures illuminate.
      AGL Visual Encyclopedia: Before and after photometry Lamp replacement LED module replacement
      An electrical systems craftsman repairing a taxiway edge light
      Photo 3. An electrical systems craftsman repairs an inoperable taxiway edge light. After a repair, verify type, position and photometric output.Credit: U.S. Air Force photo by Staff Sgt. Nick Wilson, Whiteman Air Force Base, Jan. 29, 2013. Public domain (US Government work). Source page
      Checklists

      Taxiway Lighting Photometry Checklist

      Click an item to mark it complete.

      Before testing

      Taxiway lighting drawings reviewed
      Fixture types confirmed
      Test scope defined
      Standards and specifications reviewed
      Photometer calibration verified
      Previous measurements reviewed
      Fixtures inspected
      Optical surfaces cleaned where required
      0 / 8 complete

      During testing

      Taxiway identified
      Fixture identification recorded
      Operating intensity confirmed
      Sensor position confirmed
      Measurement geometry maintained
      Required parameters measured
      Abnormal results recorded
      Questionable measurements repeated
      0 / 8 complete

      After testing

      Results analysed
      Deficient fixtures identified
      Corrective maintenance performed
      Repaired units retested
      Final report prepared
      Asset record updated
      Historical results preserved
      0 / 7 complete
      Best Practice

      Taxiway Photometry Best Practices

      1

      Use calibrated instruments

      Document calibration status and traceability.

      2

      Use consistent geometry

      Critical for meaningful comparisons.

      3

      Record the operating condition

      Intensity depends on the selected lighting step.

      4

      Test identified fixtures

      Make every result traceable to a physical location.

      5

      Clean before final acceptance

      Contamination can mask actual equipment performance.

      6

      Separate optical and electrical troubleshooting

      A poor measurement can come from either side.

      7

      Retest repaired fixtures

      Do not close an action without verification where testing is required.

      8

      Maintain baseline data

      Historical measurements support condition monitoring.

      9

      Keep criteria traceable

      Identify the source of each requirement.

      Workflow

      Recommended Taxiway Photometry Workflow

      01

      Design review

      Confirm lighting functions and applicable criteria.

      02

      Installation inspection

      Verify fixture condition and orientation.

      03

      Photometer set-up

      Verify calibration and measurement geometry.

      04

      Initial measurement

      Measure intensity and required optical parameters.

      05

      Evaluation

      Compare with applicable requirements.

      06

      Corrective maintenance

      Clean, align, repair or replace.

      07

      Retest

      Verify the correction.

      08

      Baseline record

      Preserve commissioning results.

      09

      Periodic testing

      Repeat measurements in service.

      10

      Trend analysis

      Identify degradation and recurring faults.

      Reference

      Standards and Acceptance Criteria

      FAA Taxiway Lighting Photometry

      Where FAA requirements apply, taxiway lighting photometry follows FAA fixture specifications and maintenance guidance, for example FAA AC 150/5345-46 for light fixtures and AC 150/5340-26C for maintenance, which includes photometric measurement. Confirm the current edition of each, and see FAA AC 150/5340 series explained.

      No single photometric value applies blindly to every taxiway light. Requirements vary with the following, and the final report should name the specific controlled source used for acceptance.

      ICAO provisions

      International SARPs, including Annex 14 Volume I for aerodrome visual aids.

      National authority

      National civil aviation authority requirements.

      FAA, where applicable

      FAA fixture specifications and maintenance guidance.

      Project and manufacturer

      Approved project specification, fixture design, operational category and manufacturer documentation.

      Avoid copying generic intensity values from another airport or an outdated document. Confirm the current edition of every reference before you rely on it.

      Related Guides

      ICAO Annex 14 AGL requirements FAA AC 150/5340 series explained Standards companion

      Every light in a complete taxiway lighting system.

      COMPLETE TAXIWAY LIGHTING SYSTEM RUNWAY A B → BLUE EDGE LIGHTS · OMNIDIRECTIONAL SIGNS GREEN CENTRELINE LIGHTS INTERMEDIATE HOLDING POSITION LIGHTS STOP BAR · RED RUNWAY GUARD LIGHTS · YELLOW EXIT LIGHTS · GREEN / YELLOW AIRFIELD LIGHTING CONTROL SYSTEM · SELECTIVE SWITCHING · STOP-BAR INTERLOCK · MONITORING EDGE CIRCUITBLUE EDGE LIGHTSCENTRELINE CIRCUITSSWITCHED BY SECTIONSTOP-BAR CIRCUITINTERLOCKEDHOLDING & GUARD CIRCUITYELLOW LIGHTSSCHEMATIC · LAYOUT, SPACING AND CIRCUIT COUNT ILLUSTRATIVE · NOT TO SCALE
      Figure 9. Plan view of edge, centreline, exit and stop bar lights on a link and parallel taxiway. Requirements vary by authority and project.
      AGL Visual Encyclopedia: Complete taxiway lighting system Taxiway lighting layout Taxiway edge lights

      Four checks feed one acceptance decision.

      THE 4Cs · ACCEPTANCE DECISIONCOLOURChromaticityCANDELAIntensityCOVERAGEBeam spread and aimCONFIGURATIONPlacement and layoutALL FOURMEET?YESNOACCEPTREJECTINVESTIGATERETEST123451COLOURChromaticity within its region2CANDELAIntensity meets the requirement3COVERAGEBeam spread and aim are correct4CONFIGURATIONPlacement, spacing, layout5DECISIONEvery C must pass to acceptSCHEMATIC · THE ACTUAL CRITERIA COME FROM THE STANDARD AND THE PROCEDURE
      Figure 10. Colour, candela, coverage and configuration each feed the accept or reject decision.
      AGL Visual Encyclopedia: Photometric acceptance Photometric compliance flow Report interpretation
      Final Engineering Perspective

      Taxiway lights guide aircraft only if they give the right light, in the right direction, in the right colour. Measure it, trace it to the fixture, and retest every repair.

      Calibrate. Measure. Trace. Retest.

      Test Yourself

      Quick Knowledge Check

      Q1. Why is photometry better than visual inspection alone for taxiway lights?

      A. It checks only that power arrives
      B. It gives quantitative data on intensity, distribution, colour and alignment
      C. It replaces maintenance
      D. It needs no instrument

      Q2. Why record the operating intensity step?

      A. It is optional
      B. A result at one step cannot be judged against a criterion for another
      C. Steps never change output
      D. It sets the calibration date

      Q3. What is the better maintenance sequence for a low reading on a dirty in-pavement light?

      A. Measure, replace
      B. Measure, clean, re-measure
      C. Ignore it
      D. Raise the brightness step

      Q4. Why record individual stop bar fixtures?

      A. One degraded fixture leaves a visible gap, and maintenance must find the exact unit
      B. Stop bars have only one fixture
      C. It is not needed
      D. To shorten the report

      Q5. Several taxiway lights perform abnormally at once. What should you consider first?

      A. Replace every fixture
      B. The common electrical supply
      C. Cleaning only
      D. Nothing
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      Keyword Reference

      Taxiway Lighting Types

      Taxiway lighting types

      Taxiway lighting types include edge lights, centreline lights, stop bar lights and runway guard lights, each with its own colour and purpose. Because they differ in type, each needs its own photometric test points and acceptance criteria. See the section on what to test on each taxiway light type for the method.

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      FAQ

      Taxiway Lighting Photometry FAQ

      Q1What is taxiway lighting photometry?

      The measurement and evaluation of the optical performance of taxiway visual-aid systems, including intensity, distribution, colour and alignment where applicable.

      Q2What taxiway lights can be tested photometrically?

      Depending on the airport configuration: taxiway edge lights, centreline lights, stop bars, runway guard lights and other specialized taxiway lighting.

      Q3What does a taxiway photometer measure?

      Light intensity and, depending on configuration, optical distribution, angular performance, colour-related parameters and alignment information.

      Q4Why is photometry better than visual inspection?

      Visual inspection confirms that a fixture appears to operate, while photometry gives quantitative information about its optical performance.

      Q5Can taxiway lights be bright but incorrectly aligned?

      Yes. A fixture can produce substantial output while directing its beam incorrectly, and photometric measurement can help identify this.

      Q6Why do taxiway centreline lights need special attention?

      They are frequently in-pavement and exposed to contamination, aircraft loading, moisture and mechanical stress that can affect optical performance.

      Q7Should taxiway lights be cleaned before testing?

      Where the test procedure requires it, yes. Cleaning separates contamination-related loss from an actual equipment defect.

      Q8What causes low taxiway light intensity?

      Optical contamination, degraded lamp or LED components, damaged lenses, incorrect intensity settings, electrical problems and ageing of the optical system.

      Q9Why should operating intensity be recorded?

      Measured output depends on the operating condition, so recording the intensity step makes a result meaningful and repeatable.

      Q10What should a taxiway photometric report contain?

      Airport, taxiway, fixture, test equipment, calibration status, operating condition, measurement geometry, actual results, applicable acceptance criteria, corrective actions and retest results.

      Q11How often should taxiway photometry be performed?

      It depends on authority requirements, the airport maintenance programme, lighting system, operating environment and historical performance. Do not assume a single interval for every airport.

      Field Insight

      Engineering & Expert Notes

      RS
      By Rahul Sharma
      Airfield Ground Lighting Specialist
      Test Edge, Centreline and Guidance Lights Separately
      Scope

      Each type has different requirements and positions.

      Check Colour as Well as Intensity
      Colour

      Colour checks are part of acceptance for many lights.

      Use a Repeatable Setup
      Setup

      Mark positions and record instrument details.

      Check Alignment on Directional Lights
      Alignment

      Misaligned fixtures can give poor readings.

      Clean and Re-Measure
      Maintenance

      Contamination is a common cause of low results.

      Store Baseline Data
      Records

      Use commissioning data as a reference for later tests.

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