LABORATORY PHOTOMETRY VS FIELD PHOTOMETRY
Controlled Fixture Testing vs Installed-System Verification — laboratory photometry measures an AGL fixture under controlled test conditions to characterise its intrinsic optical performance, while field photometry measures the installed lighting system under actual site conditions to verify how it performs in service. Neither replaces the other; a complete performance picture needs both.
At a Glance
| Feature | Laboratory Photometry | Field Photometry |
|---|---|---|
| Location | Controlled laboratory/test facility | Airport installation site |
| Test object | Individual fixture/product | Installed fixture/system |
| Conditions | Highly controlled | Actual environmental conditions |
| Main purpose | Product characterization and qualification | Installation/performance verification |
| Equipment | Goniophotometer and laboratory instruments | Field photometric instruments |
| Repeatability | Generally higher | More affected by site conditions |
| Beam distribution | Detailed measurement | May be more limited/practical |
| Installation effects included | No | Yes |
| Maintenance condition included | Usually new/controlled fixture | Actual operating condition |
What Is Laboratory & Field Photometry?
Laboratory Photometry
Tests an AGL fixture in a controlled laboratory environment using a goniophotometer and calibrated instruments. Position, distance, angles and environment are all controlled to determine the fixture's intrinsic photometric performance.
Question answered
What can this fixture do under controlled conditions?
Field Photometry
Evaluates the light after installation at the airport, using field photometric instruments. The measurement can reflect the actual installation geometry and operating conditions of the installed system.
Question answered
How is the installed lighting system performing in practice?
Product Performance vs Installed Performance
Easy memory: Laboratory = PRODUCT PERFORMANCE. Field = INSTALLED PERFORMANCE.
What Each Environment Controls
A laboratory test attempts to control the variables that could affect the measurement; a field measurement is exposed to the actual site.
Laboratory Variables (Controlled)
Controlled position, controlled distance, controlled angles, controlled environment, and calibrated instruments — enabling detailed and repeatable fixture characterization.
Field Factors (Actual Site)
Mounting alignment, fixture condition, lens contamination, installation geometry, surrounding lighting and environmental conditions — factors laboratory testing alone cannot capture.
Laboratory Result vs Field Result
Suppose a new runway light is tested in a laboratory and returns a peak intensity of 10,000 cd. After installation, the field measurement reflects the actual installation and operating conditions — which may differ due to misalignment, dirt or contamination, lens condition, installation orientation, electrical operating conditions, or environmental influences. The exact interpretation depends on the field test method used.
| Stage | Result |
|---|---|
| Laboratory test (new fixture) | Peak intensity: 10,000 cd |
| Field test (after installation) | Reflects actual installation and operating conditions |
Detailed Pattern vs Practical Verification
A goniophotometric test produces a detailed beam pattern, revealing the fixture's optical design.
Field testing focuses more directly on whether the installed light meets required performance at relevant locations or directions.
Strengths of Laboratory vs Field Testing
| Characteristic | Laboratory Photometry | Field Photometry |
|---|---|---|
| Peak intensity | Excellent | — |
| Detailed beam pattern | Excellent | — |
| Horizontal/vertical distribution | Excellent | — |
| Product-to-product comparison | Very useful | — |
| Installation alignment | — | Useful |
| Actual operating performance | — | Very useful |
| Effects of dirt/contamination | — | Included |
| Installation-related degradation | — | Included |
| Real-world performance | — | Primary purpose |
One of the Most Important Distinctions
Laboratory photometry does not necessarily verify that a fixture is correctly installed at the airport. Even a small installation or alignment difference can alter the direction in which the light is presented.
Laboratory
Fixture is perfectly positioned; the beam is measured exactly as designed, with no installation geometry involved.
Field
Fixture is measured as actually installed — mounting alignment and orientation can shift the beam away from the designed direction.
Controlled Condition vs Real Condition
Laboratory testing often evaluates a fixture in a controlled, usually new, condition. Field testing can reveal the real maintenance condition of an in-service fixture, including performance changes caused by dirt, lens degradation, mechanical damage, alignment changes, or ageing.
| Condition Assessed | Laboratory | Field |
|---|---|---|
| Fixture cleanliness | Clean, controlled | Actual condition (dust/contamination possible) |
| Ageing/degradation | Not captured | Captured |
| Alignment changes | Not applicable | Captured |
Runway Edge Light — Two Questions
| Test | Question It Asks |
|---|---|
| Laboratory | Does this fixture produce the required intensity distribution — candela, horizontal angles, vertical angles, beam distribution? |
| Field | Is this installed runway edge light performing correctly in its actual location, orientation and condition? |
Not Direct Substitutes
Laboratory and field photometry should not be viewed as alternatives to one another — each answers a different question, and together they form a complete performance assessment.
Myths vs Facts
Laboratory testing is optimized for controlled, repeatable and detailed fixture characterization, while field testing is optimized for assessing the installed system under actual operating conditions. Both require properly calibrated equipment and defined measurement procedures — one is not simply "more accurate" than the other.
Laboratory photometry characterizes the fixture itself, not its installation. Only a field measurement can reflect actual mounting alignment and site conditions.
Field testing is often more limited and practical in scope, and is more affected by site conditions. Detailed beam pattern and product qualification data still come from laboratory testing.
Full Engineering Parameters
| Parameter | Laboratory Photometry | Field Photometry |
|---|---|---|
| Environment | Controlled | Actual site |
| Primary focus | Fixture | Installation/system |
| Repeatability | Generally high | Depends more on field conditions |
| Detailed angular measurements | Excellent | Often more limited |
| Beam pattern | Detailed | Practical verification |
| Installation alignment | Not normally assessed | Assessed |
| Environmental effects | Minimized | Present |
| Maintenance condition | Controlled | Actual |
| Product qualification | Very suitable | Less suitable |
| Operational verification | Limited | Very suitable |
Laboratory vs Field Photometry
Laboratory photometry establishes the fixture's detailed optical characteristics; field photometry verifies how the lighting performs after installation and under real operating conditions. They are not direct substitutes.
Use laboratory data to qualify and compare products before procurement. Use field data to verify installation, alignment and in-service condition once the system is on site. Together they provide the complete performance picture — neither alone is sufficient for full AGL assurance.
For AGL: laboratory photometry proves what a fixture can do under controlled conditions; field photometry proves how it is actually performing once installed. It is generally misleading to call one "accurate" and the other "inaccurate" — each is optimized for a different purpose.
Engineering & Expert Notes
Treat Laboratory Data as the Benchmark
BaselineIt shows what the fixture can achieve. Field results show how it performs installed.
Align and Clean Before Field Measurement
PreparationRecord the condition on arrival and after cleaning.
Match Current and Step for Comparison
SettingsCompare like with like using the same CCR step.
Report the Setup With the Numbers
ReportingInclude instruments, positions and conditions.
Frequently Asked Questions
Laboratory = PRODUCT PERFORMANCE, under controlled conditions. Field = INSTALLED PERFORMANCE, under actual site conditions.
Not simply "more accurate" — laboratory testing is optimized for controlled, repeatable, detailed fixture characterization, while field testing is optimized for assessing the installed system under actual operating conditions. Both can require properly calibrated equipment and defined procedures.
No. Laboratory photometry does not necessarily verify that a fixture is correctly installed at the airport — it characterizes the fixture itself, not its installed geometry or alignment.
Possible reasons include misalignment, dirt or contamination, lens condition, installation orientation, electrical operating conditions, and environmental influences. The exact interpretation depends on the field test method used.
No — the two are complementary rather than substitutes. Laboratory testing provides detailed fixture design characterization; field testing provides installation verification. A complete performance assessment needs both.
Laboratory photometry typically uses a goniophotometer and other laboratory instruments. Field photometry uses field photometric instruments suited to on-site, installed-system measurement.
Governing Documents
For an actual project design, always verify the current edition of the applicable documents.
FAA AC 150/5340-30
Design and Installation Details for Airport Visual Aids — defines the photometric requirements a fixture must meet, forming the basis for laboratory qualification testing.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — photometric characteristics of aeronautical ground lights, including requirements referenced in both type-test and in-service assessment.
CIE Photometry Standards
International Commission on Illumination definitions and measurement methods, applicable to both goniophotometric laboratory testing and field photometric practice.
Final Engineering Note
Do not treat a laboratory type-test result as confirmation of in-service performance. Field verification is required to confirm the installed system meets the required performance at its actual location and condition.
Laboratory photometry is not field photometry — one characterizes fixture performance under controlled conditions, the other verifies installed-system performance under actual site conditions. For AGL, both together define confidence in the lighting system.
Compare the Systems. Then Learn How to Engineer Them.
Understanding the difference between AGL systems is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how AGL systems work as part of a complete airport lighting system, not just as individual components or configurations.