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Introduction. Installation variables have a real-world effect on the fixture’s Light Beam or the Field Photometrics. Disruption to the Photometric Beam effects the number of lights the pilot can see.

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  • Installation variables have a real-world effect on the fixture’s Light Beam or the Field Photometrics.

  • Disruption to the Photometric Beam effects the number of lights the pilot can see.

  • This talk focuses on the part of the photometric beam that gets obstructed by the pavement and the effect on overall the pilots view of the lights.

“The secret of a good speech is to have a good beginning and a good ending; and to have the two as close together as possible” ….

George Burns (No Relation To Burns Engineering)

Light beam obstruction elevation at light beam vs elevation at fixture edge
Light Beam ObstructionElevation at Light Beam vs. Elevation at Fixture Edge

  • FAA’s Elevation Tolerance is Measured From Fixture Edge to Low Side of the Pavement because of snow plow removal.

  • From a photometrics point of view – we care about the elevation at fixture center (not edge) where the light beam is.

  • On many projects, there exists a dispute between Contractors and Airport regarding elevation vs. photometrics.

Beam blockage vs pilot s field of view good visibility vs low visibility
Beam Blockage vs. Pilot’s Field of View(Good Visibility vs. Low Visibility)

Pilot’s point of view in good weather.

What about in low visibility
What About in Low Visibility?

  • Complicated Issue:

    • Background Light: Daytime vs. Night-Time

    • Type of Airplane – Cockpit Height.

    • Light Fixture Photometric Intensity.

    • Chromaticity.

    • Others.

Past research fog chamber
Past Research – Fog Chamber

Past research
Past Research

  • Fixtures Used:

  • R/W CTL was 5,000 candelas

  • R/W TDZ was 7,500* candelas.

  • R/W Edge was 20,000* candelas.

    • * Lower than current FAA values.

Number of lights pilot sees in low visibility1
Number of Lights Pilot Sees in Low Visibility

Visibility of Runway Lights in Nighttime Fog.

Effect beam blockage has on number of lights pilots sees in low visibility

Lower Photometric Angles are Blocked by Pavement if fixture elevation is low

Cockpit Height

Reduces the Number of Lights

Effect Beam Blockage Has on Number of Lights Pilots Sees in Low Visibility

  • Assumes that all lights have the same fixture elevation.

  • Geometric, Linear Analysis only.

  • Main Beam angles only.

Variables impacting fixture elevation at light beam
Variables Impacting Fixture Elevation at Light Beam Visibility

Transverse And Longitudinal Tilt

Fixture Elevation at Low Side of Pavement (FAA Req’t)

Tolerances of Surrounding Pavement

Design Percent Grade

Elevation of Fixture at Light Beam Exit To Adjacent Pavement

Effect on Field Photometrics & Pilots Field of View

Can the Pilot See The Lights?

Pavement tolerances grade tolerance electrical tolerance
Pavement Tolerances Visibility Grade Tolerance > Electrical Tolerance

  • Lateral: ± ¼” with 16’ Straightedge every 50’.

  • Corrective Actions only if 15% in a lot fail. Lot can cover area of 20 R/W Ctl lights.

  • Similar criteria for Longitudinal

  • Not necessarily measured where the fixture is.

Possible reasons pavement specifications tolerances

Pavement Tolerances Visibility Grade Tolerance > Electrical Tolerance

Possible Reasons: Pavement Specifications/Tolerances

FAA Spec < ¼”

Pavement tolerances

Pavement Tolerances Visibility Field Experiment

Pavement Tolerances

Field Experiment:

Measure the pavement slope next to the light fixture using a digital level.

The results showed that, in many instances, the slope around the can was 2.3% whereas theoretical was 1.5%

Tolerances effect on photometrics actual example from field
Σ Visibility Tolerances Effect On PhotometricsActual Example From Field

~ 0.288 (< 3/8”)

Fixture Height Below Grade at Light Beam =

~ 3.2 °

Photometric Angle Blocked =

Recommendations Visibility

  • Specify the Measurement Tool to be used by the Contractor to measure fixture elevation.

Recommendations Visibility

  • Perform 16’ Straight-edge Measurements for pavement tolerances at fixture locations.

  • Calculate Photometric Blockage for % Grades higher than 2.0%.

  • Specify and Inspect Base Can Level prior to pouring encasement.

  • Consider Photometrics in the Project.

The end
The End? Visibility

Pavement tolerances1
Pavement Tolerances Visibility

Measuring Fixture Height:

- The actual height will vary greatly depending on the measuring tool used. Can easily vary by 3/8”

Possible reasons1
Possible Reasons Visibility

Analyze Snow Plow Removal Procedures/Equipment

Possible reasons2
Possible Reasons Visibility


For new projects provide a detail to the Contractor or train the Contractor on the method to measure fixture elevation that most suites your Airport’s operational/snow plow removal constraints.

Possible reasons pavement specifications tolerances1
Possible Reasons: Pavement Specifications/Tolerances Visibility

  • Pavement Tolerances:

  • Lateral: ± ¼” measured every 50’ w/ 12’ Straightedge. Not necessarily measured where the fixture is going to be located.

  • Longitudinally: Measured with pfilograph. Cannot deviate by more than ½” on a single pass. ( A pass maybe ~ 500’)

  • Correction Criteria: If 15% of the measurements in a lot than corrective actions shall be taken on the pavement. (On a recent overlay project a lot was 20’ wide by 900’ long or ~ 20 R/W CTL lights).

  • At some Airports this is not aggressively regulated.

Possible reasons pavement specifications tolerances2
Possible Reasons: Pavement Specifications/Tolerances Visibility


When performing the straightedge measurement of the pavement tolerances, survey the location of the lights and measure where the lights are going to be.

Possible reasons base can tilt

Ht Visibility D Ht D

Deg Grade for 12” for 6”


1/2 0.9% 0.1” 0.05”


1 1.75% 0.2” 0.1”

Possible Reasons: Base Can Tilt.

Level !!



The end1
The End Visibility