AGL-CS-061 — Runway Edge Light Photometry Failure
The AGL Knowledge Hub | Engineering Case Study Series. A runway edge lighting photometric investigation where optical degradation caused reduced intensity, beam distortion, and chromaticity shift — from electrical verification through photometric measurement, optical inspection, and alignment restoration.
Important: This is an engineering simulation created for training. It is not presented as an actual airport incident. All readings, values, dates and outcomes are illustrative, and no airport, organisation, person or manufacturer is identified or implied.
1Case Study Overview
During a scheduled airfield lighting photometric inspection, a section of runway edge lights was found to be significantly below the required photometric intensity, even though the lights were operating electrically and no CCR alarms were present.
Pilots had also reported that the runway edge lights appeared dim and difficult to identify during wet-night operations, particularly from intermediate approach distances.
The Constant Current Regulator (CCR) was maintaining the selected 6.6 A current, output voltage was normal, and all affected fixtures were illuminated.
A detailed photometric investigation was initiated covering light intensity, beam distribution, chromaticity, fixture alignment, optical contamination, and LED optical performance.
The investigation identified severe optical degradation caused by lens contamination, UV-related lens aging, reflector deterioration, and minor fixture misalignment, resulting in failure to meet ICAO Annex 14 photometric requirements.
This case demonstrates that a runway edge light can be electrically operational while failing photometric compliance and providing inadequate runway visual guidance.
2Learning Objectives
After completing this case study, the learner should be able to:
- Diagnose runway edge light photometric failures.
- Differentiate electrical and photometric defects.
- Evaluate runway edge light intensity.
- Assess beam distribution and alignment.
- Verify chromaticity compliance.
- Investigate optical degradation.
- Restore ICAO-compliant photometric performance.
3System Background
A runway edge light consists of:
- LED optical module.
- Optical lens.
- Beam-control optics.
- Reflector assembly.
- Housing.
- Mounting system.
- Electrical driver.
Photometric performance depends on:
- Peak intensity.
- Vertical beam distribution.
- Horizontal beam distribution.
- White chromaticity.
- Lens transmission.
- Optical cleanliness.
- Fixture alignment.
Common photometric failure causes include:
- Lens contamination.
- UV degradation.
- Optical scratching.
- LED lumen depreciation.
- Reflector deterioration.
- Internal condensation.
- Fixture misalignment.
- Incorrect replacement components.
4Problem Statement
The reported condition was:
- Runway edge lights illuminated.
- Reduced apparent brightness.
- Poor wet-night visibility.
- CCR healthy.
- No electrical alarms.
- Photometric inspection failed.
Are the runway edge lights electrically healthy but photometrically non-compliant with ICAO Annex 14 requirements?
5Initial Observations
| CCR status | Healthy |
| Circuit operation | Normal |
| Light operation | ON |
| Visual brightness | Reduced |
| Wet-night visibility | Poor |
| Beam appearance | Non-uniform |
The lights were electrically operational, but their optical performance was degraded.
6Initial Engineering Hypotheses
The maintenance team considered:
CCR current reduction.
Transformer under-voltage.
Lens contamination.
LED optical degradation.
Fixture misalignment.
7Photometric Failure Principle
A runway light can be electrically functional but operationally inadequate.
8Test Equipment
The investigation used:
- Portable AGL photometer.
- Goniophotometric measurement equipment.
- Chromaticity meter.
- Optical inspection tools.
- True-RMS multimeter.
- Fixture alignment instruments.
- Thermal imaging camera.
- ICAO Annex 14 photometric reference data.
- Airport-approved PPE.
9Investigation
Step 1: Verify Electrical Operation
Results:
| CCR operation | Normal |
| Current regulation | Normal |
| Secondary voltage | Normal |
| Fixture operation | Normal |
No electrical fault was identified.
Step 2: Photometric Measurement
Measured peak intensity:
32,000 cd
Required intensity:
≥ 50,000 cd (representative training value)
The fixture failed the photometric requirement.
Step 3: Beam Distribution Measurement
Testing showed:
- Reduced peak intensity.
- Vertical beam depression.
- Horizontal beam narrowing.
- Non-uniform intensity distribution.
The beam no longer matched the required photometric envelope.
Step 4: Chromaticity Measurement
Measured chromaticity showed:
- Slight shift toward warm white.
- Reduced color consistency.
- Optical aging effects.
The emitted light remained generally white but showed measurable degradation.
Step 5: Optical Inspection
Inspection revealed:
- Dirt accumulation.
- Rubber deposits.
- Surface scratching.
- UV-related lens hazing.
- Reduced optical transparency.
Lens transmission had deteriorated significantly.
Step 6: Internal Optical Inspection
The optical assembly showed:
- Reflector discoloration.
- Optical contamination.
- LED lens aging.
- Internal moisture staining.
Optical efficiency had decreased.
Step 7: Fixture Alignment Verification
Measurements showed:
- Vertical aiming error.
- Slight outward rotation.
- Reduced runway-edge coverage.
- Inconsistent beam overlap.
Alignment errors further reduced effective runway guidance.
10Root Cause
The runway edge light photometric failure was caused by combined optical degradation, including:
- Lens contamination.
- UV-related lens aging.
- Reflector deterioration.
- LED optical degradation.
- Minor fixture misalignment.
The electrical system remained healthy, but the fixture no longer produced ICAO-compliant intensity and beam distribution.
11Corrective Action
The maintenance team:
- Removed the affected fixture.
- Replaced the optical lens assembly.
- Replaced the degraded optical module.
- Restored reflector condition.
- Cleaned the optical compartment.
- Realigned the fixture.
- Performed photometric testing.
- Verified beam distribution.
- Confirmed chromaticity compliance.
- Updated photometric maintenance records.
12Post-Repair Verification
The runway edge light met ICAO photometric requirements after repair.
13Root-Cause Analysis
Dim runway edge light
Healthy
Below requirement
Non-compliant
Contaminated and aged
Degraded
Optical degradation and photometric deterioration
Replace optical components and restore alignment
14Why This Case Was Important
Photometric failures can cause:
- Reduced runway conspicuity.
- Poor edge definition.
- Wet-night visibility problems.
- ICAO non-compliance.
- Reduced visual range.
- Increased operational risk.
Photometric testing is essential for runway lighting performance verification.
15Engineering Lessons
An illuminated runway edge light is not necessarily ICAO compliant.
An illuminated runway edge light is not necessarily ICAO compliant.
Photometric testing is separate from electrical testing.
Photometric testing is separate from electrical testing.
Lens contamination can significantly reduce runway-edge intensity.
Lens contamination can significantly reduce runway-edge intensity.
Fixture alignment directly affects beam distribution.
Fixture alignment directly affects beam distribution.
Optical aging is a major long-term photometric degradation mechanism.
Optical aging is a major long-term photometric degradation mechanism.
16Engineer's Decision Point
You observe: Runway edge lights ON. Pilots report poor wet-night visibility. CCR healthy. No electrical faults. What should you investigate first?
17Knowledge Check
18Interview Questions
Quick Reference: Runway Lighting Photometry Procedure, Equipment, FAA Photometry & Guard Lights
A runway lighting photometry procedure sets the measurement distance, aligns the photometric head with the beam axis, records the output at each brightness step and compares it with the required values. Runway lighting photometry equipment is a calibrated photometric head, a data logger and alignment aids.
FAA runway lighting photometry requirements apply where the project cites FAA documents. Runway guard light photometry is tested in the same way as other fixtures, using the requirements for that light type.
19Frequently Asked Questions
Quick answers about runway edge light photometric failure and ICAO Annex 14 compliance.
Q1What is AGL-CS-061?
AGL-CS-061 is an engineering training case study on a runway edge light that is electrically healthy but fails photometric requirements because of optical degradation. It covers intensity, beam distribution, chromaticity, alignment and optical inspection, through to corrective action and post-repair verification. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2Can a runway edge light be working electrically but still fail ICAO Annex 14 requirements?
Yes. A light can be illuminated, with the CCR holding the correct current and no alarms, and still fall short on intensity, beam distribution or chromaticity. Electrical health and photometric compliance are separate checks, and a lit fixture is not automatically a compliant one.
Q3How do you tell an electrical fault from a photometric failure?
Verify the electrical side first: CCR operation, current regulation, secondary voltage and fixture operation. If these are normal but the lights look dim or the beam looks uneven, the problem is likely optical. Photometric measurement then confirms it by comparing measured intensity and beam distribution against the required values.
Q4What causes runway edge light photometric failure?
Common causes include lens contamination, UV-related lens aging, optical scratching, LED lumen depreciation, reflector deterioration, internal condensation, fixture misalignment and incorrect replacement components. In this case, several of these combined: contaminated and aged lenses, degraded reflector and LED optics, and minor misalignment.
Q5Why did pilots report poor visibility in AGL-CS-061?
The fixtures produced reduced peak intensity and a distorted beam. In the training scenario the measured peak was 32,000 cd against a representative requirement of at least 50,000 cd. Combined with wet-night conditions, this made the edge lights dim and harder to identify from intermediate approach distances.
Q6Which test equipment is used for a runway edge light photometric investigation?
The case uses a portable AGL photometer, goniophotometric measurement equipment, a chromaticity meter, optical inspection tools, a true-RMS multimeter, fixture alignment instruments and a thermal imaging camera, with ICAO Annex 14 photometric reference data. All work must follow the airport's approved procedures, with appropriate PPE.
Q7Why does fixture alignment matter for photometric performance?
Beam distribution depends on the fixture being aimed correctly. Vertical aiming error or outward rotation reduces runway-edge coverage and creates inconsistent beam overlap, so even a good optical module can give poor runway guidance if it is misaligned.
Q8What was the root cause in AGL-CS-061?
Combined optical degradation: lens contamination, UV-related lens aging, reflector deterioration, LED optical degradation and minor fixture misalignment. The electrical system remained healthy, but the fixture no longer produced ICAO-compliant intensity and beam distribution.
Q9How was compliance restored after the fault was found?
The maintenance team replaced the optical lens assembly and degraded optical module, restored the reflector condition, cleaned the optical compartment and realigned the fixture. They then repeated photometric testing, verified beam distribution and chromaticity, and updated the photometric maintenance records.
Q10Why should runway edge lights undergo periodic photometric testing?
Optical performance degrades gradually through contamination, aging and misalignment, often without any electrical alarm. Periodic photometric testing detects this loss before it reduces runway conspicuity or breaches ICAO Annex 14 requirements.
Engineering & Expert Notes
Electrically Healthy Does Not Mean Optically Compliant
PrincipleUse photometric checks to confirm intensity and distribution, not only that the light is on.
Clean First, Then Measure
MethodContamination is the simplest explanation. Record before-and-after readings.
Check Alignment Before Condemning the Optics
AlignmentA slightly turned fixture can look like a weak one.
Trend Photometric Results by Fixture Age
TrendingGradual loss shows when lenses and modules need planned replacement.
20Case Study Conclusion
Runway edge light photometric failure is an optical-performance problem caused by lens contamination, optical aging, reflector deterioration, and beam misalignment, and a runway edge light can be electrically operational while failing ICAO Annex 14 photometric requirements and providing inadequate runway visual guidance.
Systematic photometric measurement, beam-distribution verification, chromaticity testing, optical inspection, LED assessment, and fixture alignment verification can identify photometric failures and restore compliant runway edge lighting performance.
In AGL engineering, the aircraft crew judges the runway by the light they see, not by the current flowing in the circuit, and photometric compliance is the true measure of runway edge lighting performance.
Turn Case Studies Into Engineering Capability
A case study shows you how a problem is investigated. Precision AGL Academy helps you build the knowledge to understand why it happens, diagnose it systematically, and apply the right engineering approach.
Study real-world-style engineering scenarios, identify failure patterns, understand root causes, and develop a systematic approach to AGL troubleshooting.
Study the case. Understand the system. Build the skill.
Follow the Academy
Important Notice, Disclaimer & Limitation of Liability
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 electrical personnel. It is not professional engineering, legal or regulatory advice, and using it does not create any professional or client relationship.
- Fictional training simulation. This case study is an engineering simulation created for training. It is not a report of an actual airport incident. Scenarios, sequences, dates, readings, measurements, outcomes and numerical values are illustrative and invented for teaching. No fault, failure, cause or liability is attributed to any person, company, airport, regulator, manufacturer or product, and any resemblance to a real event is coincidental. The content is not a forensic, legal, insurance, regulatory or accident-investigation finding and must not be cited as evidence, as a record of an event, or as a basis for disciplinary, contractual, insurance or legal action.
- Safety. Work on series circuits, constant current regulators (CCRs), isolating transformers, cables, connectors and control 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. Where a case narrates an inspection, measurement or test, that narrative is not an instruction or an endorsement of the method.
- Values, test results and acceptance. Test voltages, insulation-resistance and current values, tolerances, thresholds, photometric and angular figures and pass/fail or “acceptable” wording in a case are specific to its invented scenario. They are not acceptance criteria, limits or targets. Use the project specification, the applicable standard and the manufacturer’s data for real work. Completing or following a case produces no test certificate, calibration record, acceptance or evidence of compliance.
- Aviation operations. Nothing here authorises return to service, a change of operating category (CAT I/II/III), a NOTAM, a flight inspection outcome or any aerodrome certification decision. These rest with the aerodrome operator, the air navigation service provider and the competent regulator.
- Standards and regulations. References to ICAO, FAA, IEC, IEEE, ISO and other standards are for orientation only. They are summarised, may be incomplete or out of date, and standards are revised from time to time. Consult the current official editions. Following this content does not guarantee compliance with any law, standard or regulatory approval. Official documents, regulations and manufacturers’ instructions always prevail.
- Learning aids. Knowledge checks, decision points, interview questions, FAQs and suggested answers are teaching aids with illustrative answers. They are not an assessment, certification, accreditation or competency or authorisation to work on any aerodrome, and they do not predict or guarantee the outcome of any job interview or application.
- Generic content; no warranty. Diagnostic sequences, cause rankings, tolerances and values are generic and indicative; real installations differ in design, equipment make and model, age and condition. Content is provided “as is” and “as available”, without warranty of any kind, express or implied, including accuracy, completeness, currency or fitness for a particular purpose.
- Limitation of liability. To the fullest extent permitted by applicable law, Precision AGL Academy and its owners, authors and contributors are not liable for any injury, death, loss, damage, downtime, penalty or regulatory consequence, whether direct or indirect, arising from the use of, reliance on, or inability to use this content. Nothing in this notice excludes or limits any liability that cannot lawfully be excluded or limited.
- Independence and trademarks. This is an independent publication, not affiliated with or endorsed by ICAO, the FAA, the IEC, DGCA, any airport, regulator or equipment manufacturer. Third-party names, standard designations and trademarks belong to their respective owners and are used for identification only.
- Copyright and use. © 2026 Precision AGL Academy. All rights reserved. You may read this page and use it for personal reference and internal training, keeping this notice attached. Any other copying, republication, redistribution, scraping or commercial use requires our prior written permission.
- Corrections. Content is reviewed periodically, with no obligation to update. To report an error, safety concern or rights issue, write to precisionaglsolutions@gmail.com.