An Airfield Ground Lighting (AGL) system can appear to be functioning normally while its photometric performance is gradually deteriorating. The lights may illuminate. The electrical circuits may be healthy. The Constant Current Regulator (CCR) may operate without alarms. Yet the light reaching the pilot may no longer meet the photometric requirements specified by ICAO Annex 14 or FAA standards.
This is why photometric testing is one of the most important verification activities in airport lighting engineering. It confirms not only that a light works, but that it provides the correct intensity, colour, and beam distribution required for safe aircraft operations. One of the most common questions from airport operators is: how often should AGL photometry actually be carried out? The answer is not a fixed annual interval — it depends on the operational condition of the airfield, maintenance activities, regulatory requirements, and the airport's maintenance strategy.
Photometry should be planned according to engineering risk, not a fixed calendar. Electrical operation does not guarantee photometric compliance — the two must be verified separately.
There Is No Universal Testing Interval
Unlike routine electrical inspections, ICAO Annex 14 does not prescribe a single mandatory photometric testing frequency applicable to every airport. It does, however, expect preventive maintenance on precision approach runways (CAT II/III) to include field measurement of the intensity, beam spread and orientation of approach and runway lights, and it treats certain lights as unserviceable when their main-beam average intensity falls below 50% of the specified value. Beyond that, airport operators are responsible for ensuring that all visual aids continue to meet the required performance throughout their service life. In India, check the photometric and maintenance provisions of DGCA CAR Section 4, Series B, Part I and the conditions of the aerodrome licence, since national rules and the approved maintenance programme can set specific intervals.
This means photometry should be planned according to engineering risk rather than waiting for visible failures. The objective is straightforward:
Verify that the lighting system still delivers the visual performance expected by the pilot.
How often should airport lighting be inspected?
There is no single fixed interval. For photometric inspection, ICAO Annex 14 does not prescribe one mandatory frequency for every airport, so the interval is set by the airport operator as part of its preventive maintenance programme. It depends on traffic volume, environmental conditions, fitting age, LED vs. halogen technology, local procedures and regulatory oversight. In addition, inspect photometrically after new installation, after major maintenance, after realignment of fixtures, and before regulatory audits or operational upgrades. Confirm routine visual and electrical inspection intervals against your own maintenance procedures and regulator.
When Should Photometric Testing Be Performed?
Rather than a fixed calendar, photometric testing is triggered by specific events and conditions across the lifecycle of the lighting system:
These are the moments that matter — not a date on a calendar, but a change in condition, configuration, or scrutiny.
Why Waiting for a Failure Is the Wrong Strategy
Many lighting systems continue to operate electrically even while their optical performance degrades. Common causes include:
Without photometric testing, these issues may remain unnoticed until they affect operational safety or trigger audit observations. By that stage, corrective maintenance becomes more disruptive and expensive.
Electrical operation does not necessarily mean photometric performance is acceptable.
The Benefits of Regular Photometry
Routine photometric testing provides much more than a simple pass-or-fail result. It enables airports to:
- Establish baseline performance after installation
- Monitor gradual degradation over time
- Identify underperforming fittings early
- Verify maintenance quality
- Support predictive maintenance programmes
- Reduce unexpected failures and optimise maintenance budgets
Photometric data transforms maintenance decisions from reactive to evidence-based.
The Cost of Not Testing
Skipping scheduled photometric verification can lead to a range of operational and financial consequences:
| Risk | Consequence |
|---|---|
| Undetected degradation | Operational restrictions or reduced runway availability |
| Reactive maintenance | Emergency maintenance and unexpected fitting replacements |
| No performance history | Increased lifecycle costs and non-conformities during audits |
| No verification data | Reduced confidence in the visual guidance system |
The cost of a structured photometric inspection programme is generally far lower than the cost of operational disruption caused by undetected performance degradation.
Photometry Is an Investment in Safety
Some organisations still view photometric testing as an optional compliance exercise. In reality, it is an essential engineering tool. Electrical tests confirm that the system is powered. Photometric tests confirm that the system performs its intended operational function. Both are equally important for safe aircraft operations.
Photometry is a risk-control measure that helps ensure pilots receive the visual guidance they depend on during every take-off and landing.
When Photometry Should Be Triggered
Event-driven, not calendar-driven
Conclusion
There is no single timetable that applies to every airport. However, the engineering principle is universal: photometry should be performed whenever there is a possibility that lighting performance has changed, and at planned intervals to verify continued compliance.
Airfield lighting is a safety-critical system. Its performance should never be assumed. It should be measured.
- Perform photometry after installation and commissioning
- Re-test after major maintenance or fixture replacement
- Verify performance after alignment adjustments
- Include periodic photometric inspections in preventive maintenance
- Confirm compliance before audits and operational upgrades
- Use photometric data to support predictive maintenance
Electrical operation does not guarantee photometric compliance.
Frequently Asked Questions
How often should AGL photometry be performed?
There is no universal interval. ICAO Annex 14 does not prescribe a single mandatory photometric testing frequency for every airport, so photometry should be planned according to engineering risk and the operator's preventive maintenance programme, not a fixed calendar. Factors include traffic volume, environmental conditions, fitting age, LED or halogen technology, local procedures and regulatory oversight.
Does Annex 14 say anything about photometric checks at all?
Annex 14 expects preventive maintenance on precision approach runways (CAT II/III) to include field measurement of the intensity, beam spread and orientation of approach and runway lights. It also treats certain lights as unserviceable when their main-beam average intensity falls below 50% of the specified value. In India, check the provisions of DGCA CAR Section 4, Series B, Part I and the aerodrome licence conditions.
When should photometric testing be triggered?
Testing is event-driven: after new installation and before operational service, after major maintenance that could affect optical performance, after realignment of fixtures, during periodic compliance verification and before regulatory audits or operational upgrades. A change in condition, configuration or scrutiny is the trigger, not a date on a calendar.
Why is waiting for a failure the wrong strategy?
Many lighting systems keep operating electrically while optical performance degrades. Common causes include ageing LEDs, reflector deterioration, prism contamination, UV ageing of lenses, water ingress and optical misalignment. These issues can go unnoticed until they affect safety or trigger audit observations.
Does a lit light with a healthy CCR mean photometry is fine?
No. Electrical operation does not guarantee photometric compliance, and the two must be verified separately. The lights may illuminate and the CCR may run without alarms, yet the light reaching the pilot may no longer meet Annex 14 or FAA requirements.
What are the benefits of regular photometry?
It establishes baseline performance after installation, monitors gradual degradation, identifies underperforming fittings early and verifies maintenance quality. It also supports predictive maintenance and helps reduce unexpected failures and optimise maintenance budgets.
What are the risks of not testing?
Undetected degradation can lead to operational restrictions or reduced runway availability, reactive maintenance leads to emergency fitting replacements, and no performance history increases lifecycle costs and audit non-conformities. The cost of a structured photometric programme is generally far lower than the cost of operational disruption.