PHOTOMETRIC REQUIREMENT VS ELECTRICAL REQUIREMENT

At a Glance

Think "Light" vs "Electricity"

       ELECTRICAL INPUT
              ↓
          LED / LAMP
              ↓
        OPTICAL SYSTEM
              ↓
       LIGHT OUTPUT
              ↓
     Candela / Distribution

       POWER SUPPLY
              ↓
        ELECTRICAL SYSTEM
              ↓
      Voltage / Current
              ↓
    Insulation / Protection
              ↓
       SAFE OPERATION

Photometric vs Electrical Requirements

Worked Example: LED Runway Edge Light

The same fixture carries both types of requirements, verified through entirely different tests.

LED RUNWAY LIGHT
      ↓
Light intensity
      ↓
Candela
      ↓
Horizontal distribution
      ↓
Vertical distribution
      ↓
Colour
      ↓
Beam coverage

LED RUNWAY LIGHT
      ↓
Input/current
      ↓
LED driver
      ↓
Protection
      ↓
Insulation
      ↓
Dielectric strength
      ↓
Electrical safety

Candela vs Current

Suppose an AGL fixture operates from a constant-current series circuit.

6.6 A
  ↓
LED driver / optical system
  ↓
Required light output
  ↓
Candela

The 6.6 A is electrical. The resulting candela is photometric.

Electrical Compliance Does Not Mean Photometric Compliance

A fixture can pass its electrical tests but still fail photometry.

Voltage/current       ✓
Insulation            ✓
Dielectric withstand  ✓
Functional operation  ✓
                       ↓
Photometry             ✗

Possible reasons include:

• Incorrect LED output
• Optical degradation
• Wrong lens
• Poor optical alignment
• LED aging
• Manufacturing variation

Electrical pass ≠ photometric pass.

Photometric Compliance Does Not Mean Electrical Compliance

The reverse is also possible — a fixture can produce the correct light distribution while having an electrical problem.

Candela distribution   ✓
Colour                 ✓
Beam spread            ✓
                       ↓
Insulation resistance  ✗

Photometric pass ≠ electrical pass. Both need to be verified independently.

Photometry Test

Typical photometric verification uses a goniophotometer or another appropriate calibrated photometric system.

        AGL FIXTURE
             ↓
      Controlled input
             ↓
       Goniophotometer
             ↓
     Angular measurement
             ↓
      Candela values
             ↓
    Photometric curve
             ↓
      Compare with limits

Typical output includes candela tables, polar curves, horizontal and vertical distribution, and colour data.

Electrical Tests

Photometric Requirement vs Electrical Requirement in FAT

AGL System Example

Consider a complete runway lighting circuit. Electrical requirements run throughout the system, while photometric requirements sit primarily at the fixture/optical level.

       CCR
        ↓
     AGL Cable
        ↓
Isolation Transformer
        ↓
   LED Fixture
        ↓
    LIGHT OUTPUT

Photometric vs Electrical vs Functional

It's useful to distinguish three categories rather than just two.

How Each Requirement Gets Verified

Example Compliance Matrix

Every row here ends in a pass/fail result, but the requirement type determines which instrument and which limit applies.

Important Relationship

Electrical performance can affect photometric performance, even though the two remain different requirements.

CCR current
      ↓
Fixture input
      ↓
LED driver
      ↓
LED output
      ↓
Optical output
      ↓
Candela

If the electrical current is incorrect, the light output may also be incorrect — but they remain different requirements, each needing its own verification.

LED AGL Fixture Breakdown

Constant-current compatibility
Operating current
Surge protection
Power consumption
Driver efficiency
Insulation
Dielectric withstand
Grounding

Candela
Beam spread
Horizontal distribution
Vertical distribution
Colour
Angular coverage
Intensity stability

How to Remember the Difference

"Can it safely and
correctly handle
electricity?"
      ↓
ELECTRICAL
      ↓
Electricity
      ↓
V / A / W / Ω / MΩ

"Does it produce the
required light in the
required direction?"
      ↓
PHOTOMETRIC
      ↓
Light
      ↓
cd / distribution / colour

Photometric Requirement vs Electrical Requirement

A proper AGL FAT/SAT dossier should keep electrical, photometric and functional requirements separately identified, even though they interact during actual operation.

Engineering & Expert Notes

Frequently Asked Questions

Governing Documents

For an actual project design, always verify the current edition of the applicable documents.

Photometric and electrical requirements are not two versions of the same check — one verifies the light a fixture produces, the other verifies how it handles electricity to produce it.

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