AGL Photometry
Measuring the light that guides aircraft. AGL photometry is the systematic measurement and evaluation of the optical performance of airfield lighting — intensity, distribution, colour and alignment — converting visual judgment into objective engineering data for commissioning, inspection, maintenance and troubleshooting.
What Is AGL Photometry?
AGL photometry is the systematic measurement of the light produced by an airfield lighting installation. Unlike a visual inspection, which primarily determines whether a light appears to be operating correctly, photometry uses measurement equipment to quantify its optical performance.
A photometric assessment can examine intensity, intensity distribution, horizontal and vertical distribution, colour, beam characteristics, alignment, uniformity and spacing-related performance — of individual fixtures and of an installed lighting system.
Beyond "Is It ON?"
The objective is not simply to determine whether a fitting is illuminated — it's to determine whether the lighting system is providing the required visual performance.
Quantified, Not Judged
Photometry converts the visual performance of a lighting system into measurable engineering data rather than a subjective impression.
Serves Visual Guidance
AGL exists to give pilots visual guidance on approach, landing, takeoff and ground movement — photometry verifies that this purpose is actually being met.
Why Is AGL Photometry Required?
AGL photometry is required because a light can be electrically healthy and still fail to give the pilot the intensity, colour and beam distribution the standard specifies. Dirt on the optics, ageing, misalignment and lamp or LED changes all reduce light output without tripping an electrical test. Photometry is the way to verify optical performance, at commissioning and periodically in service.
Electrically Healthy Isn't the Same as Optically Correct
An AGL fixture may be electrically healthy but still have poor optical performance — a condition that isn't always obvious during a normal visual inspection.
Hidden Failure Modes
A fitting may illuminate but produce insufficient intensity, have an incorrect beam direction, degraded optical components, incorrect colour, misalignment, contamination on the optical surface, damaged or degraded LEDs, or an abnormal intensity distribution.
Questions Photometry Answers
- Is the light producing the required intensity?
- Is the light distributed in the correct direction?
- Is the colour within specification?
- Is the fitting correctly aligned?
- Are there abnormal variations between fixtures?
- Has optical performance deteriorated over time?
What Does AGL Photometry Actually Measure?
Photometry is more than measuring brightness. The optical performance of an AGL system is considered through several distinct parameters.
1. Intensity
The amount of luminous power emitted by a light source in a particular direction, commonly expressed in candela (cd). The required intensity depends on the lighting system, fixture type, direction and applicable standard.
2. Distribution
A light may have sufficient peak intensity but still distribute it incorrectly. Photometric measurement examines how intensity changes across defined angular positions.
3. Colour
Colour is part of the visual coding used by aerodrome lighting systems. Photometric measurement verifies whether emitted light falls within the applicable colour requirements — and can help identify colour shift, LED degradation, or an optical/filter problem behind an incorrect reading.
4. Alignment
The direction a fixture emits light is critical. A correctly functioning LED module that is physically misaligned may provide inadequate guidance to an aircraft.
5. Uniformity / System
For installed systems, measurements are evaluated across multiple fixtures or positions to identify abnormal variations and overall system performance.
The Full Picture
None of these parameters stands alone — a complete photometric assessment considers intensity, distribution, colour and alignment together against the applicable requirement.
AGL Photometry Is Not the Same as Lux Measurement
A common misunderstanding is to treat AGL photometry as simply measuring lux. For most AGL applications, the important parameter is luminous intensity in a specified direction, expressed in candela.
AGL photometry is primarily concerned with the directional optical performance of the lighting system — how much light a fixture emits in a specified direction — not simply how much light falls on a surface. This distinction is particularly important when evaluating runway, taxiway and approach lighting.
AGL Photometry Across Different Systems
Different AGL systems have different photometric requirements. Click through the categories below.
Runway Lighting
Runway edge, centreline, touchdown zone, threshold and runway end lights.
- Low-intensity fixtures
- Incorrect beam orientation
- Colour and optical degradation
- Fixture-to-fixture variation
Taxiway Lighting
Taxiway edge, centreline, stop bar and runway guard lighting.
- Edge/centreline light performance
- Colour, intensity, alignment
- Fixture condition
Approach Lighting
Careful evaluation of intensity, direction, colour, alignment and configuration.
- Individual light performance
- System-level consistency
PAPI / VASI
Visual approach slope indicators require specialised assessment of optical characteristics and alignment.
- Vertical angular characteristics
- Colour transition
- Unit-to-unit consistency
Illuminated Signs
Luminance/brightness, colour, uniformity and module performance.
- Individual module performance
- Overall sign illumination
Common Thread
Every system above is evaluated for the same underlying question: is the lighting providing the required visual performance in the direction it needs to?
PAPI / VASI Photometry & Alignment
PAPI performance depends not only on whether units are illuminated, but on the optical geometry and vertical distribution of the emitted light — photometry and alignment are closely connected here.
Photometric verification of a PAPI system can support evaluation of light intensity, vertical angular characteristics, colour transition, alignment and unit-to-unit consistency along the approach slope indication.
Each unit's red/white transition sits at a slightly different vertical angle — together the row gives the pilot a slope reading
PAPI Intensity Testing
PAPI intensity testing measures the intensity of each unit's red and white beams with a PAPI photometer, together with the red/white transition angle and unit-to-unit consistency. Compare the results with the PAPI photometric requirements of the applicable standard at each brightness step, and repeat after lamp or LED replacement or realignment.
AGL Photometry Equipment
Field photometry requires suitable measurement equipment and controlled measurement procedures — appropriate to the type of AGL installation being evaluated.
A Typical Photometry Setup Includes
Calibration is critical. Photometric measurements are only useful when the measurement equipment is properly calibrated and the measurement setup is controlled — a technically accurate instrument cannot compensate for incorrect measurement geometry.
What Equipment Is Used for AGL Photometry?
AGL photometry uses a calibrated photometer or photometric head, a measurement frame or positioning system, colour measurement capability, alignment aids such as an inclinometer, and a data logger with analysis software. The calibration certificate for the instrument goes with every report.
Airport Photometer & Photometric Testing Equipment
An airport photometer is a calibrated instrument that measures the light output of airfield lighting in a defined direction. Choosing the right photometric testing equipment for the airport, and keeping its calibration current, decides whether the numbers in a photometry report can be trusted.
What Is a Runway Lighting Photometer?
A runway photometer (also called a runway lighting photometer) is a calibrated light-measurement system used to measure the intensity of runway lights, either in the field or against a fixture on a test bench. In practice the same airport photometer is used across taxiway, approach and stop bar lighting. A PAPI photometer is set up differently, because it must also resolve the vertical angle at which the red/white transition occurs.
Photometric Testing Equipment Airport Teams Use
This airport light testing equipment, which also serves as runway lighting photometry equipment, is typically assembled as follows:
Luminous Intensity Measurement Airport Method
It means measuring candela in a specified direction, and in the field it is usually done with a photometric head placed at a known distance along the measurement axis. The meter reads illuminance (lux) at the head, and intensity is derived using the inverse-square relationship, I = E × d², so the measurement distance must be known and the head must be far enough from the fixture for the relationship to hold.
Luminous intensity measurement airport teams carry out follows the same order each time: fix the measurement distance, align the head with the beam axis, record the reading at each CCR brightness step, and compare the result with the required photometric values.
Airport Light Beam Measurement & Airport Light Beam Angle Measurement
Airport light beam measurement records intensity at a grid of horizontal and vertical angles. Airport light beam angle measurement then describes how wide and how high the useful beam is and where its axis points. Together these results can be compared with the fixture's isocandela diagram to confirm both distribution and aiming.
Airport Photometer Calibration & Photometer Calibration Certificate
Airport photometer calibration compares the instrument against a reference standard that is traceable to a national standard, normally in an accredited laboratory (ISO/IEC 17025; NABL in India). The result is a photometer calibration certificate, which should state the instrument identification, calibration date, calibration factors or results, measurement uncertainty, traceability and the due date for re-calibration. Re-calibrate at the interval set by the manufacturer or project specification, and after any shock, damage or repair. File the certificate with every photometry report that uses the instrument.
Runway Lighting Photometry Equipment
Runway lighting photometry equipment is a calibrated photometer, portable or on a bench, with a measurement frame, alignment aids and a data logger. For runway lights it is set on the fixture's measurement axis at a known distance. A PAPI photometer is set up differently because it must also resolve the vertical angle of the red/white transition.
How Is a Photometer Calibrated?
A photometer is calibrated by comparing it with a reference standard traceable to a national standard, normally in an accredited laboratory (ISO/IEC 17025; NABL in India). The laboratory issues a calibration certificate with the results, uncertainty and re-calibration due date. Re-calibrate at the interval set by the manufacturer or specification, and after any shock, damage or repair.
The Field AGL Photometry Process
A typical field photometry activity, organized into ten steps across four phases. Tick items off as you work through a project — this resets on reload.
Plan
Inspect & Verify
Measure
Analyse & Report
Correct measurement geometry is one of the most important aspects of AGL photometry. A photometric result is meaningful only when the measurement position, viewing direction, fixture position and reference geometry are correctly established. Errors can arise from incorrect fixture or instrument positioning, incorrect measurement distance, poor alignment, or uncontrolled field conditions.
Airport Lighting Photometry Procedure: Runway & Taxiway
The airport lighting photometry procedure follows the same logic for every system: fix the geometry, set the circuit to a known brightness step, measure, and compare against the applicable criteria. The runway photometry procedure and taxiway photometry procedure differ mainly in fixture type, colour and the criteria applied. Airfield lighting photometric testing and airport light intensity measurement are repeated at commissioning and periodically in service.
Runway Lighting Photometry Procedure
Runway fixture photometry and runway light measurement cover edge, centreline, touchdown zone, threshold and runway end lights.
- Identify fixture type and brightness step
- Set up the photometer on the defined axis
- Measure intensity and colour
- Compare against the criteria
Taxiway Photometry Procedure
Taxiway light measurement covers edge, centreline, stop bar and runway guard lights.
- Confirm colour coding (blue edge, green centreline)
- Measure at the specified angles
- Check alignment and fixture condition
- Record fixture-to-fixture variation
Runway Lighting Current Measurement
Light output depends on the CCR current, so photometry is only meaningful if the circuit current is known.
- Record CCR output current at each step
- Repeat photometry across brightness steps
- Note any current drift during the test
Light Intensity Testing by Light Type
| Light type | Test | What to confirm |
|---|---|---|
| Runway edge / centreline | Runway light intensity testing (runway light photometric testing) | Intensity, colour and alignment at each brightness step |
| Touchdown zone | Touchdown zone light intensity | Intensity and alignment against the applicable criteria |
| Runway threshold | Runway threshold light intensity | Green colour and intensity in the specified direction |
| Runway end | Runway end light intensity | Red colour and intensity |
| Taxiway edge / centreline | Taxiway light intensity testing (taxiway lighting photometric test) | Blue edge / green centreline colour, intensity and alignment |
| Stop bar | Stop bar photometry | Red colour, intensity and beam direction toward the holding position |
| Runway guard light | Runway guard light photometry | Yellow colour, intensity and alignment |
| Approach lighting | Approach lighting photometric testing | Intensity, aiming and consistency along the system |
| PAPI | PAPI intensity testing | Intensity, red/white transition angle and unit-to-unit consistency |
How Is Runway Light Intensity Measured?
Runway light intensity is measured by setting the circuit to a defined brightness step, placing a calibrated photometer on the specified measurement axis at a known distance, and recording the reading at each required angle. The intensity in candela is derived from the reading and the distance, then compared with the criteria for that fixture.
How Is Taxiway Light Intensity Measured?
Taxiway light intensity measurement uses the same method as runway lights, with the criteria for taxiway edge, centreline, stop bar or guard fixtures applied. Colour is checked at the same time, because taxiway lights are colour-coded and a colour shift can make a fixture non-compliant even when intensity is acceptable.
Runway Fixture Photometry & Runway Light Measurement
Runway fixture photometry and runway light measurement cover edge, centreline, touchdown zone, threshold and runway end lights. For each fixture, measure intensity and colour at the required angles and brightness steps, then compare the results with the criteria for that fixture type.
Taxiway Light Measurement
Taxiway light measurement covers edge, centreline, stop bar and runway guard lights. Check colour together with intensity, because taxiway lights are colour-coded, and record fixture-to-fixture variation.
Runway Threshold Light Intensity & Runway End Light Intensity
Runway threshold light intensity is measured in the specified direction with the green colour confirmed. Runway end light intensity is measured with the red colour confirmed. Both are compared with the criteria for the fixture and application at each brightness step.
Runway Guard Light Photometry
Runway guard light photometry confirms the yellow colour, intensity and alignment of each light against the criteria for the fixture type and application.
Photometry at Different CCR Intensity Settings
Many AGL systems use multiple intensity steps controlled by the Constant Current Regulator (CCR). Photometric evaluation may need to consider more than a single operating condition — select a step to see how a series circuit's fixtures should respond, and how a degraded fixture stands out.
What Step-Testing Can Reveal
Individual Fixture vs. Installed System Photometry
Individual Fixture Evaluation
Focuses on one fitting.
- Factory testing
- Incoming inspection
- Troubleshooting
- Replacement verification
- Maintenance
- Failure investigation
Installed System Evaluation
Focuses on the lighting system in its actual field environment.
- Commissioning
- Acceptance testing
- Periodic inspection
- Performance verification
- Airport maintenance
- Compliance assessment
Same photometric parameters, two very different measurement environments
Commissioning vs. Periodic Photometry
During Commissioning
Establishes whether newly installed lighting performs as intended. Early detection is valuable because correcting a problem during commissioning is generally easier than discovering it after the airport system is already in routine operation.
- Incorrect fixture orientation
- Poor alignment
- Incorrect colour or low output
- Wiring/configuration issues
Periodic (In-Service)
AGL performance changes over time — LED ageing, optical contamination, mechanical movement, water ingress, environmental exposure and component degradation all contribute. Instead of only asking "is the light working?", periodic photometry lets maintenance teams ask "how has the optical performance changed?"
Photometry & AGL Maintenance
Photometric data is useful not only for acceptance but also for maintenance decision-making.
| Photometric Result | Recommended Response |
|---|---|
| Normal measurement | Continue operation / routine monitoring |
| Gradual reduction | Investigate degradation |
| Sudden abnormal result | Inspect fixture, alignment, electrical supply and optical components |
| Incorrect colour | Inspect LED/module/filter/optical system |
| Abnormal distribution | Inspect alignment and optical assembly |
Common AGL Photometry Problems
Electrical testing alone cannot establish complete AGL performance — click a card to see the likely cause.
Low intensity
Possible Cause
- LED degradation
- Lamp issue
- Optical contamination
- Electrical problem
Incorrect colour
Possible Cause
- LED/module degradation
- Optical/filter issue
Uneven intensity
Possible Cause
- Optical degradation
- Component variation
- Contamination
Wrong beam direction
Possible Cause
- Fixture misalignment
One fixture significantly different
Possible Cause
- Fixture/component problem
Multiple fixtures low
Possible Cause
- Circuit issue
- CCR issue
- Common-system issue
Sudden performance change
Possible Cause
- Maintenance error
- Damage
- Configuration change
Good electrical test, poor photometry
Possible Cause
- Optical problem
- Alignment problem
Photometry vs. Electrical Testing vs. Visual Inspection
These are different, complementary testing disciplines. Electrical testing tells you whether the system is electrically healthy; photometry tells you whether the lighting is performing visually as required.
| Discipline | Checks | Measures | Detects |
|---|---|---|---|
| Visual Inspection | What can we see? | Whether a light appears ON | Obvious visible defects |
| Electrical Testing | Electrical condition | Insulation, continuity, current/voltage | Electrical faults |
| Photometry | Optical performance | Intensity, colour, distribution, alignment | Optical faults |
Photometry Data Analysis
Raw measurements are only the beginning — the engineering value comes from converting measurement data into useful conclusions.
Where measurements are repeated over time, historical data can also be compared to identify performance trends — turning a single photometric snapshot into a maintenance trend line.
The AGL Photometry Report
A professional photometry report provides sufficient information to make the measurements traceable.
Project Information
Airport, project, location, date, lighting system, fixture type.
Measurement Information
Measurement equipment, calibration information, configuration, locations, operating conditions.
Results
Photometric and colour measurements, distribution data, alignment observations, pass/fail evaluation.
Observations
Damaged fixture, contamination, misalignment, low output, colour deviation, installation issue.
Conclusion
An engineering summary of the measured system performance.
Traceability
Every value should trace back to a calibrated instrument, a defined geometry and a recorded operating condition.
Runway, Taxiway & PAPI Photometric Reports and Checklists
A photometry report is the permanent record of a measurement campaign. The headings are the same for every system, but the content differs for runway, taxiway and PAPI work.
Runway Photometric Report
A runway photometry report records each runway fixture measured, its intensity and colour results at each brightness step, alignment observations and pass/fail status against the applicable criteria.
Taxiway Photometric Report
A taxiway photometric report covers edge, centreline, stop bar and guard lights, with colour results and fixture-to-fixture variation recorded alongside intensity.
PAPI Photometric Report
A PAPI photometric report records intensity, red/white transition angle and aiming for each unit, with the calibration certificate of the instrument attached.
Runway Photometry Checklist
Runway Photometry Report
A runway photometry report records each fixture measured, its intensity and colour results at each brightness step, alignment observations and pass or fail status. Attach the photometer calibration certificate, then sign and file the report.
AGL Photometry Standards & References
Photometric requirements depend on the particular AGL system and applicable regulatory/technical criteria. Do not evaluate every AGL fixture against one universal photometric criterion — the required performance depends on the lighting system, fixture/application and applicable standard.
Annex 14, Volume I and applicable aerodrome design and lighting provisions.
AC 150/5340 series and applicable equipment specifications.
Applicable Indian standards for the relevant AGL equipment.
Airport/project-specific technical specifications and manufacturer requirements.
Airfield Lighting Photometric Design, Requirements, Inspection & Taxiway Lighting Intensity
Airfield lighting photometric design
Airfield lighting photometric design is the design stage where the required light output is turned into a layout. Fixture intensity and beam distribution, spacing, mounting and aiming are chosen so the lighting meets the photometric requirements across the area it serves. Fixture isocandela data comes from the manufacturer, and the result should be checked against the standard being followed.
Airfield lighting photometric requirements
Airfield lighting photometric requirements set the minimum intensity, beam pattern and colour that each type of light must achieve. They come from ICAO Annex 14 and national or FAA specifications, and differ by light type and category of operation. Please confirm the exact requirements in the edition you follow. See Photometric Requirements & Photometry in India below.
Airfield lighting photometric inspection
Airfield lighting photometric inspection is the field check that installed lights give the light output and alignment they should. It uses calibrated measuring equipment and a defined method, and the results are recorded and compared with the requirement and earlier readings. It finds problems such as dirt, misalignment and ageing that a visual check can miss.
Taxiway lighting intensity
Taxiway lighting intensity is the light output of taxiway edge and centreline lights at each brightness step. The required values depend on the light type and the visibility conditions the system supports, and come from the standard. Intensity is checked by photometric measurement, because a taxiway light can still look lit while giving too little output.
Photometric Requirements & Photometry in India
Airport photometric requirements are set per system and per fixture, not by one universal figure. The sections below show where runway, taxiway and PAPI requirements come from.
Runway Photometric Requirements
Runway photometric requirements define intensity, beam coverage and colour for each runway light type, and are usually presented as isocandela diagrams in ICAO Annex 14, the FAA AC 150/5340 series and the project specification.
Taxiway Photometric Requirements
Taxiway photometric requirements follow the same approach for taxiway edge, centreline, stop bar and guard lights, with the applicable colour and beam requirements for each.
Airport Photometric Requirements
Airport photometric requirements also cover approach lighting and illuminated signs. The airport's technical specification may add manufacturer or project-specific limits on top of the regulatory baseline.
PAPI Photometric Requirements
PAPI photometric requirements concern both intensity and the vertical angular setting of each unit's red/white transition, so a PAPI is verified for angle as well as brightness.
AGL Photometry in India
Airport photometry in India, including runway photometry, is normally specified through the aerodrome's technical specification, which refers to ICAO Annex 14, the aerodrome regulator's requirements and the relevant Indian Standards for the equipment. AGL photometry is carried out at commissioning to establish the baseline, and periodically in service to track performance. For measurement planning, calibration and reporting on Indian aerodromes, get in touch.
AGL Photometry Workflow
This creates a traceable engineering loop from installation to verified performance. Photometry becomes significantly more valuable when connected with other AGL information — a low photometric output leads to checking the fixture, alignment, optical condition, secondary voltage/current, isolating transformer and series-circuit condition, then repeating photometry once the fault is corrected.
The 4 Dimensions of AGL Performance
Complete AGL verification requires looking beyond a single test — four complementary dimensions describe a fully verified system.
Electrical
Is the electrical system operating correctly?
Photometric
Is the lighting producing the required optical performance?
Mechanical
Are fixtures, transformers, connectors and mounting arrangements physically sound?
Operational
Does the system operate correctly through its control, intensity and monitoring functions?
Quick Knowledge Check
Q1. AGL photometry is primarily concerned with measuring which unit?
Q2. A fixture that is electrically healthy but misaligned would most likely be caught by:
Q3. Why might photometry need to be repeated at multiple CCR intensity steps?
Explore More AGL Engineering
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Open the Standards Companion →AGL Design & Electrical Engineering
The series-circuit design decisions that shape optical output.
Open AGL Design →AGL Testing & Inspection
Field verification alongside photometric measurement.
Open Testing & Inspection →AGL Installation & Commissioning
Photometric acceptance as part of commissioning.
Open Installation & Commissioning →PAPI Engineering Guide
Photometry applied to a specific precision visual aid.
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The optical and electrical principles behind the measurements.
Open Physics of AGL →Measure. Analyse. Verify.
AGL Photometry turns lighting performance into engineering data. Explore the principles, equipment, analysis techniques and practical applications.
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Frequently Asked Questions
Q1What is AGL photometry?
AGL photometry is the systematic measurement and evaluation of the optical performance of airfield lighting, covering intensity, distribution, colour and alignment. It converts visual judgment into objective engineering data used in commissioning, inspection, maintenance and troubleshooting.
Q2How is photometry different from a visual inspection?
A visual inspection primarily determines whether a light appears to be operating correctly. Photometry uses measurement equipment to quantify its optical performance, so it can establish whether the lighting system provides the required visual performance, not just whether a fitting is illuminated.
Q3What does AGL photometry measure?
It considers intensity (commonly in candela), distribution across angular positions, colour against the applicable colour requirements, alignment of the direction the fixture emits light, and uniformity across multiple fixtures or positions in an installed system. None of these stands alone; a complete assessment considers them together against the applicable requirement.
Q4Is AGL photometry the same as measuring lux?
No. For most AGL applications the important parameter is luminous intensity in a specified direction, expressed in candela, not illuminance in lux. Lux describes how much light falls on a surface and depends on distance and angle, whereas AGL photometry is concerned with the directional optical performance of the fixture.
Q5Why can an electrically healthy AGL fixture still fail photometry?
A fitting may illuminate yet produce insufficient intensity, have an incorrect beam direction, degraded optical components, incorrect colour, misalignment, contamination on the optical surface, damaged or degraded LEDs, or an abnormal intensity distribution. These conditions are not always obvious during a normal visual inspection.
Q6What questions does photometry answer?
It answers whether the light produces the required intensity, is distributed in the correct direction, is within colour specification and correctly aligned, whether there are abnormal variations between fixtures, and whether optical performance has deteriorated over time.
Q7Which airfield lighting systems are assessed photometrically?
Runway lighting, taxiway lighting, approach lighting, PAPI and VASI, and illuminated signs. Each has its own requirements: for example, runway and taxiway lights are checked for intensity, colour, alignment and fixture-to-fixture variation, while signs are assessed for luminance, colour, uniformity and module performance.
Q8How is a PAPI system checked photometrically?
PAPI performance depends on optical geometry and vertical distribution as well as illumination. Photometric verification can support evaluation of light intensity, vertical angular characteristics, red and white colour transition, alignment and unit-to-unit consistency. An error in any one unit shifts the glide-path indication given to the pilot.
Q9Why is fixture alignment part of photometry?
The direction a fixture emits light is critical. A correctly functioning LED module that is physically misaligned may still provide inadequate guidance to an aircraft, so alignment is measured against the design axis alongside intensity, distribution and colour.
Q10When is AGL photometry used?
It is used across commissioning, inspection, maintenance and troubleshooting, and it can help identify colour shift, LED degradation, contamination or optical problems, and deterioration of optical performance over time.
Q11Why is AGL photometry required?
AGL photometry is required because it verifies that airfield lighting gives pilots the visual guidance it was designed to give. A light can be switched on and electrically healthy while its intensity, colour or aiming has drifted out of specification. Photometry measures those properties objectively at commissioning and during service, so that degradation is found before it affects safety.
Q12How is runway light intensity measured?
A calibrated photometer is placed on the specified measurement axis at a known distance from the fixture, with the circuit set to a defined brightness step. Readings are taken at the required angles, and the intensity in candela is derived from the reading and the distance, then compared with the criteria for that fixture. The CCR current is recorded alongside, because output depends on it.
Q13How is taxiway light intensity measured?
Taxiway light intensity is measured the same way as runway light intensity: a calibrated photometer, a known distance and a defined brightness step. The criteria for the specific taxiway fixture (edge, centreline, stop bar or guard light) are applied, and colour is checked at the same time because taxiway lights are colour-coded.
Q14What equipment is used for AGL photometry?
Typical equipment includes a calibrated airport photometer with a photometric head, colour measurement capability, positioning and alignment aids such as an inclinometer, a data logger with analysis software, and a valid calibration certificate for the instrument. PAPI work needs a set-up that can also resolve the vertical angle of the red/white transition.
Q15What is a runway lighting photometer?
A runway lighting photometer is a calibrated instrument that measures the luminous intensity of runway lights in a defined direction. It is used in the field or on a test bench, and the same type of airport photometer is generally used for taxiway, approach and stop bar lighting.
Q16How is a photometer calibrated?
A photometer is calibrated by comparing it against a reference standard that is traceable to a national standard, normally in an accredited laboratory. The laboratory issues a calibration certificate showing the calibration results, uncertainty, traceability and re-calibration due date. It is repeated at the interval set by the manufacturer or project, and after any damage.
Q17What is the airport lighting photometry procedure?
The procedure is to identify the fixture type and applicable criteria, inspect and clean the installation, verify the photometer and its calibration, fix the measurement geometry, set the circuit to a known brightness step and record the current, capture intensity and colour data, and compare the results with the criteria. Deviations are investigated, and everything is documented in a photometry report.
Engineering & Expert Notes
Photometry Answers a Different Question From Electrical Testing
PrincipleElectrical tests show the circuit is working; photometry shows whether the light is correct in intensity, colour and direction.
Installed Performance Can Differ From Laboratory Data
InstallationMounting, aiming, contamination and surrounding surfaces change the delivered light. Verify on site, not only from data sheets.
Test at Several CCR Steps Where Required
StepsLight output changes with current. Use the steps specified for the test and record them with the readings.
Baseline Data Is Valuable
BaselineEarly measurements make later degradation visible. Store them in a form that can be compared year after year.
Clean Before You Condemn
MaintenanceDirty optics can mimic a failed fixture. Clean and recheck before replacing equipment.
Document Equipment and Conditions
RecordsInstrument calibration and test conditions are part of the result. Without them, the numbers are hard to trust.
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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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