AGL Photometric Testing Guide
The practical field guide to verifying that runway, taxiway, approach and PAPI lighting delivers the required intensity, distribution, colour and alignment — equipment, field measurement, evaluation, reporting and troubleshooting.
What Is AGL Photometry?
The measurement and evaluation of the photometric performance of Airfield Ground Lighting systems.
AGL photometry verifies whether installed runway, taxiway, approach and PAPI lighting provides the required light intensity, distribution, colour and alignment for its operational function. It is carried out during commissioning, periodic inspection, maintenance, rehabilitation, troubleshooting and performance verification. A properly planned inspection helps identify degraded light output, incorrect beam alignment, colour deviations, optical contamination and installation problems that can affect the visual aids pilots rely on.
The objective is not simply to determine whether a light is ON or OFF. A fixture can operate electrically and still fail photometrically — through optical degradation, incorrect aiming, contamination, damaged lenses or filters, incorrect installation, lamp or LED degradation, mechanical movement, incorrect transformer or circuit conditions, or measurement setup errors.
Electrical Serviceability
Does the fixture light up and carry current correctly?
Photometric Serviceability
Does the light deliver the required intensity, distribution, colour and alignment?
Two Different Checks
Electrical serviceability and photometric serviceability are different aspects of AGL inspection.
New to the topic? This page is the practical field guide. For the concepts — candela vs lux, isocandela diagrams and what photometry measures — start with AGL Photometry.
Why Is Photometric Testing Required?
Objective evidence that the installed system continues to perform to the applicable design and acceptance requirements.
New Installation
Verify performance of newly installed lighting before commissioning and operational acceptance.
Commissioning
Establish that the completed installation meets the specified photometric requirements.
Periodic Inspection
Identify deterioration in lighting performance over time.
Preventive Maintenance
Verify performance after maintenance activities and component replacement.
Rehabilitation
Establish the condition of existing lighting before and after rehabilitation work.
Troubleshooting
Investigate abnormal performance, uneven brightness, incorrect beam coverage or alignment problems.
Airport audits and acceptance. Photometric measurements can form part of technical inspection, acceptance documentation and airport lighting performance records.
AGL Photometric Testing Equipment
A professional survey needs suitable, calibrated equipment configured for the lighting facility under test.
Airport Photometer
Measures photometric performance of airfield lighting — intensity, angular distribution, colour, beam characteristics and values at defined positions. It should suit the type of AGL facility under test.
Runway Photometer
Used for runway edge, threshold, end, centreline, touchdown zone and approach lighting. The arrangement must correspond to the applicable test geometry and requirements.
PAPI Photometer
Evaluates PAPI optical characteristics: intensity, beam coverage and alignment, colour transition, vertical angular characteristics and horizontal coverage. Highly sensitive to geometry and alignment.
Measurement System
- Photometer and light sensor
- Positioning system and measurement frame
- Angular measurement arrangement
- Data acquisition equipment and software
- Reference targets or alignment aids
- Calibration documentation
| Pre-survey verification | What to confirm |
|---|---|
| Calibration | Instrument identification, calibration validity, traceable certificate |
| Instrument condition | Sensor condition, battery condition, zero/reference condition where applicable |
| Configuration | Measurement configuration, software and settings |
Measurement Frame & Sensor Positioning
The physical position and orientation of the sensor are critical.
Errors in sensor height, distance, horizontal position, vertical angle, azimuth, fixture orientation or reference point can produce incorrect photometric results.
Establish the measurement setup before testing and keep it consistent throughout the survey.
Runway Light Photometry
Each runway lighting facility has its own operational function and photometric characteristics.
| Facility | What is verified | Notes |
|---|---|---|
| Runway edge lights | Intensity, beam distribution, colour, orientation, fixture condition, uniformity between test points | Provide lateral guidance and define the usable runway edges |
| Threshold lights | Required colour, intensity, angular coverage, alignment, individual fixture performance | |
| Runway end lights | Required colour, intensity, beam coverage, alignment, fixture condition | |
| Centreline lights | Relevant intensity and distribution characteristics where installed | Particularly important for precision approach runways and enhanced visual guidance |
| Touchdown zone lights | Evaluated per the applicable photometric arrangement and measurement requirements | |
| Approach lighting | Intensity, distribution, alignment, colour, system configuration, individual light performance | Multiple unit types and configurations |
Taxiway Photometry
Taxiway lighting provides visual guidance for aircraft ground movement.
Taxiway Edge Lights
- Intensity
- Colour
- Beam distribution
- Alignment
- Fixture condition
Taxiway Centreline Lights
Where installed, evaluated for specified photometric performance and colour characteristics.
Stop Bars
A critical visual aid associated with runway entry control.
- Intensity and colour
- Beam coverage
- Individual fixture performance
- Circuit operation
Runway Guard Lights
- Correct operation
- Intensity and colour
- Flashing characteristics where applicable
- Alignment and visibility
Photometric inspection should be considered together with the operational function of the lighting facility.
PAPI Photometry
Its photometric performance is closely tied to the accuracy of the visual glide-path indication given to the pilot.
Intensity
Verify the PAPI light units produce the required light output.
Beam Coverage
The beam should provide the required horizontal and vertical coverage.
Beam Alignment
Each unit's angular position is critical — guidance relies on the relationship between the red and white portions of the beam.
Colour
The white-to-red transition must be clearly defined and within applicable requirements.
Vertical Angle
Vertical angular characteristics of each unit are a key part of performance verification.
Geometry
Measurement geometry matters as much as the readings themselves.
PAPI photometry is not simply an intensity test. Measurement geometry, beam alignment and colour transition are equally important.
The AGL Photometry Procedure
A structured procedure gives repeatable, traceable results.
1. Preparation
Review the test requirement; identify the lighting facilities to be tested; review drawings, runway/taxiway configuration and previous photometric reports; prepare test forms; verify equipment and calibration status; coordinate with airport operations and ATC as required.
2. Calibration verification
Verify photometer ID, certificate and validity, sensor condition, power supply, software and settings. Record equipment details in the report.
3. System inspection
Visually check for damaged fixtures, dirty lenses, broken components, incorrect orientation, loose fittings, obstructions, water ingress, cable or connector issues, transformer issues and abnormal light output — separating physical problems from true photometric deficiencies.
4. Measurement setup
Confirm reference point, distance, sensor height and orientation, horizontal and vertical position, angle and fixture identification. Keep the method consistent.
5. Field measurement
Operate at the required condition and record at selected units, defined points, CCR intensity steps and angular positions. Each measurement must be traceable to its location.
6. Data evaluation
Compare against applicable requirements: intensity, distribution, colour, alignment, coverage, uniformity. Do not fail a fixture merely because it looks dim.
7. Failure identification
Identify the probable cause: degradation, contamination, aiming, optical damage, LED/lamp, transformer, connector, cable, CCR output, installation error or measurement error.
8. Rectification
Clean, realign, replace fixture or optical parts, replace transformer, repair connector or cable, investigate the CCR, correct mechanical faults.
9. Retest
Repeat the relevant measurement to confirm the problem is resolved and the requirement is now met.
10. Final report
Issue a complete, traceable report: project and airport/runway details, test date, weather/visibility where relevant, equipment and calibration information, methodology, measurement locations, raw and evaluated results, pass/fail status, deficiencies, corrective actions, retest results, photographs, test personnel and approval/sign-off.
Common AGL Photometry Failures
Tap a card to see possible causes.
Low intensity
Possible causes
- Lamp / LED degradation
- Optical contamination
- Damaged lens
- Incorrect CCR setting
- Transformer problem
- Electrical supply issue
- Fixture degradation
Incorrect colour
Possible causes
- Damaged colour filter
- Optical degradation
- Incorrect light source
- Fixture contamination
- Measurement equipment issue
Poor alignment
Possible causes
- Mechanical movement
- Incorrect installation
- Damaged mounting
- Maintenance error
- Settlement of supporting structure
Damaged optical system
Possible causes
- Cracked lens
- Damaged filter
- Clouded optical window
- Water contamination
- Internal optical damage
Contamination
Possible causes
- Dirt and dust
- Oil
- Moisture
Incorrect installation
Possible causes
- Fixture height
- Orientation and position
- Aiming
- Spacing / geometry
Sensor positioning error
Possible causes
- Incorrect distance
- Incorrect sensor height
- Incorrect angle
- Incorrect reference point
- Sensor misalignment
Obstruction & interference
Possible causes
- Temporary obstructions
- Permanent obstructions
- Surrounding environment
Wiring & transformer issues
Possible causes
- Series circuit
- Isolating transformer
- Primary / secondary connector
- Cable
- CCR
- Fixture connections
Photometry and the AGL Electrical Chain
Photometry should never be considered independently from the electrical system.
A photometric deficiency may require investigation across the complete chain. For low light intensity, work from the fixture back: fixture condition → optical system → secondary connection → isolating transformer → primary circuit → CCR output. This avoids replacing a fixture when the real problem is elsewhere in the series circuit.
The Photometric Report
Enough information for another engineer to understand what was done, and why.
A professional report answers: What was tested? How? With what equipment? Where were measurements taken? What values were measured? Which requirement applied? Which points failed? What corrective action was taken? What were the retest results?
| Report sections | ||
|---|---|---|
| 1. Cover page | 8. Measurement geometry | 15. Photographs |
| 2. Project information | 9. Lighting system configuration | 16. Conclusion |
| 3. Scope of testing | 10. Measurement results | 17. Test personnel |
| 4. Applicable standards | 11. Pass/fail evaluation | 18. Approval / signatures |
| 5. Test equipment | 12. Deficiency register | 19. Calibration certificates |
| 6. Calibration details | 13. Corrective actions | 20. Supporting drawings |
| 7. Test methodology | 14. Retest results |
AGL Photometry Documentation
Good photometry is not only about measurement — it is also about traceability.
What & where
- Airport
- Runway / taxiway
- Lighting facility
- Fixture identification
- Measurement location
How & with what
- Test date and test condition
- Photometer identification
- Calibration information
Results & action
- Measured values
- Acceptance criteria
- Pass / fail status
- Deficiencies and corrective actions
- Retest results
Keep the history. Historical records help identify gradual degradation and recurring problems — a single result tells you the condition today; a series of results tells you the trend.
Photometry During AGL Maintenance
Verify that maintenance restored intended performance — not just electrical operation.
Photometric testing is especially useful after fixture replacement, major AGL maintenance, runway or taxiway rehabilitation, PAPI adjustment, approach lighting maintenance, significant pavement works, fixture realignment and lighting system modification.
Photometry vs Visual Inspection
They serve different purposes.
| Check | Visual inspection | Photometric testing |
|---|---|---|
| Light ON / OFF | Yes | Yes |
| Physical damage | Yes | May identify effect |
| Lens contamination | Yes | Yes |
| Light intensity | Subjective | Measured |
| Beam alignment | Limited | Measured |
| Colour | Visual indication | Measured / evaluated |
| Beam distribution | Limited | Measured |
| Performance verification | Limited | Yes |
| Numerical test results | No | Yes |
| Trend monitoring | Limited | Yes |
Photometric Testing at Different CCR Intensity Steps
Verification should consider the applicable test condition for the facility and measurement requirement.
AGL systems operate at different intensity steps through the Constant Current Regulator (CCR). The purpose is to establish whether the system delivers the required performance under the specified operating condition.
When investigating abnormal results, comparing performance across CCR steps can reveal fixture response problems, circuit abnormalities, transformer issues, CCR-related issues and non-linear or abnormal light output.
Photometry Troubleshooting Approach
When a measurement fails, avoid immediately replacing the fixture.
1. Confirm the measurement
Equipment, calibration, sensor position, measurement geometry and test settings.
2. Inspect the fixture
Lens, optical components, cleanliness, alignment, mechanical condition.
3. Check the secondary circuit
Secondary connector, transformer, fixture connection.
4. Check the primary circuit
Primary connector, cable, series circuit.
5. Check the CCR
Output current, intensity step, circuit condition, monitoring indications.
6. Repeat the measurement
After corrective action, perform a controlled retest.
AGL Photometry Standards & References
Always evaluate against the applicable edition and specific facility requirements — not generic numerical values.
Annex 14, Volume I; Airport Design Manual; applicable guidance on visual aids.
Requirements for airport lighting and visual aids.
Applicable national aviation authority requirements.
Airport technical specifications, project specifications, manufacturer documentation and approved design drawings.
Important: acceptance values, test geometry and measurement methods vary by lighting facility, operational category, applicable standard and project specification. Always use the controlled project reference for the installation under test.
AGL Photometry Workflow
From plan to traceable report.
| Stage | What happens |
|---|---|
| Plan | Define scope, facilities, test conditions and acceptance requirements |
| Prepare | Verify equipment, calibration, drawings and safety/operational coordination |
| Inspect | Check the physical condition of the lighting system |
| Set Up | Establish the correct measurement geometry and sensor position |
| Measure | Record photometric data systematically |
| Evaluate | Compare results with the applicable requirements |
| Identify | Locate failed or abnormal lighting points |
| Rectify | Correct the underlying problem |
| Retest | Verify the effectiveness of the corrective action |
| Report | Issue a complete and traceable photometric report |
Photometry Field Checklist
Tap to tick items off as you work through a survey.
Plan & Prepare
Verify & Set Up
Measure & Evaluate
Rectify & Report
8 Key Principles of AGL Photometry
01 — A light being ON does not prove photometric compliance.
Electrical operation and photometric performance are different checks.
02 — Measurement geometry matters.
Incorrect sensor position can produce incorrect results.
03 — Calibration matters.
Measurements need controlled, traceable equipment.
04 — Alignment matters.
A working fixture can still give incorrect visual guidance if misaligned.
05 — Colour matters.
Intensity alone does not establish complete photometric performance.
06 — Troubleshoot the complete circuit.
The cause may be upstream of the fixture.
07 — Always retest after rectification.
A repair should be verified by measurement.
08 — Record everything.
Data is valuable when traceable and comparable over time.
Measure correctly. Evaluate objectively.
Rectify systematically. Retest and record. Photometry is a complete engineering verification process — equipment, geometry, configuration, electrical systems, optical performance, alignment, colour, evaluation and corrective action.
Explore the AGL Engineering Knowledge Hub
Fundamentals
Standards & Compliance
Runway, Taxiway & Approach Lighting
Surface Movement & Safety
PAPI
Electrical Engineering & Power
Photometry & Testing
Maintenance, Inspection & Safety
Resources, Documentation & Careers
Frequently Asked Questions
Q1What is AGL photometry?
AGL photometry is the measurement and evaluation of the photometric performance of Airfield Ground Lighting systems, including intensity, distribution, colour and alignment as applicable.
Q2What is an airport photometer?
An airport photometer is a measurement instrument designed or configured to measure the photometric performance of airport visual aids and lighting systems.
Q3What is a runway photometer?
A runway photometer measures the photometric characteristics of runway lighting facilities such as edge, threshold, centreline and other applicable runway lights.
Q4What is PAPI photometry?
PAPI photometry is the measurement and evaluation of the optical performance of a PAPI system, including intensity, beam coverage, colour and angular characteristics.
Q5How is runway lighting tested?
Using a defined measurement procedure and suitable photometric equipment. The measurement geometry, test points and acceptance criteria depend on the particular runway lighting facility and applicable requirements.
Q6How is taxiway lighting tested?
By measuring the applicable photometric characteristics of taxiway edge, centreline, stop bar, runway guard and other installed lighting facilities.
Q7Why is runway light intensity testing important?
It provides objective evidence that the lighting system produces the required visual guidance performance under the specified test conditions.
Q8Can a light pass visual inspection but fail photometry?
Yes. A fixture may appear operational while producing inadequate intensity, incorrect beam distribution, incorrect colour or incorrect alignment.
Q9How often should AGL photometry be carried out?
The required frequency depends on the applicable aviation authority requirements, airport procedures, project specifications, operational requirements and the maintenance programme.
Q10Is photometry required after AGL maintenance?
Where specified by the maintenance procedure or applicable requirements, photometric verification can confirm that the lighting system still meets its required performance after maintenance or adjustment.
Q11What causes low AGL light intensity?
Potential causes include optical contamination, lamp or LED degradation, damaged optical components, incorrect CCR output, transformer problems, connector or cable issues, fixture degradation or measurement errors.
Q12What causes PAPI photometric failure?
Possible causes include incorrect unit alignment, optical degradation, contamination, damaged components, incorrect measurement geometry or other system configuration issues.
Q13What information should an AGL photometric report contain?
Project details, scope, equipment and calibration information, measurement methodology, test geometry, measured results, acceptance criteria, deficiencies, corrective actions, retest results and supporting records.
Calculators & Tools
Work with real photometric data.
Comparisons
Common photometry questions, side by side.
SOPs, Forms & Checklists
Procedures, forms and inspection checklists for photometric work.
Related AGL Engineering Guides
Explore related technical subjects.
Engineering & Expert Notes
Electrical Health Is Not Optical Performance
PrincipleFixtures can draw correct current while delivering poor intensity or colour. Photometric checks confirm what the pilot actually sees.
Calibrate and Document the Measurement Setup
EquipmentRecord instrument identity, calibration status and sensor position. Results are only credible when the setup can be reproduced.
Control Ambient Light and Surface Conditions
ConditionsStray light and contamination affect readings. Choose suitable conditions and clean optics before measurement, noting what was done.
Alignment Errors Can Look Like Low Intensity
AlignmentCheck aiming before concluding that a unit is under-performing. A correctly aimed unit may measure very differently from a misaligned one.
Trend Results Against a Baseline
TrendingCompare each measurement with commissioning data. Gradual change is easier to see and act on than a single reading.
Report What Was Measured and How
ReportingInclude method, location, conditions and instrument details so another engineer could understand and repeat the test.
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Please read before relying on any content on this page or on any record downloaded from it.
- Purpose and intended users. This page is an independent educational and informational reference for competent, suitably trained and authorised airfield ground lighting (AGL) and aerodrome personnel. It is not professional engineering, legal or regulatory advice, and using it creates no professional or client relationship. Learning-path and Academy references describe stages of learning only and are not a certification, accreditation or authorisation.
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