Evaluation of In-Pavement Runway 

Guard Lights 

James W. Patterson, Jr.

December 2004 

DOT/FAA/AR-TN04/49 

This document is available to the public through the National 

Technical Information Service (NTIS), Springfield, Virginia 22161. 

U.S. Department of Transportation 

Federal Aviation Administration

o

t

e t

e

c

h

n

i

c

a

l n

o

t

e t

e

c

h

n

i

c

a

ote technical note technic

a
NOTICE 

This document is disseminated under the sponsorship of the U.S. 

Department of Transportation in the interest of information exchange. The 

United States Government assumes no liability for the contents or use 

thereof. The United States Government does not endorse products or 

manufacturers. Trade or manufacturer's names appear herein solely 

because they are considered essential to the objective of this report. This 

document does not constitute FAA certification policy. Consult your local 

FAA airports office as to its use. 

This report is available at the Federal Aviation Administration William J. 

Hughes Technical Center’s Full-Text Technical Reports page: 

actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF). 
Technical Report Documentation Page

1. Report No.

DOT/FAA/AR-TN04/49

2. Government Accession No. 3. Recipient's Catalog No.

 4. Title and Subtitle 

EVALUATION OF IN-PAVEMENT RUNWAY GUARD LIGHTS 

5. Report Date

December 2004

6. Performing Organization Code

ATO-P R&D 

7. Author(s)

James W. Patterson, Jr.

8. Performing Organization Report No. 

9. Performing Organization Name and Address

Federal Aviation Administration 

William J. Hughes Technical Center 

Airport Technology 

10. Work Unit No. (TRAIS)

Research and Development Branch 

Atlantic City International Airport, NJ 08405 

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration

13. Type of Report and Period Covered

 Technical Note

Office of Aviation Research 

Washington, DC 20591

14. Sponsoring Agency Code

 AAS-100

15. Supplementary Notes

Tom Paprocki of Hi-Tec Systems Inc. provided technical support throughout the course of this evaluation.

16. Abstract

In-pavement Runway Guard Lights are a series of alternate-flashing yellow, unidirectional in-pavement lighting fixtures 

(L-852G) equally spaced along a runway holding position marking that are only visible to aircraft approaching the hold position

from the taxiway side of the fixture. In some instances, however, problems have been encountered where pilots have reported the 

lights visible from the opposite side of the fixtures, i.e., to aircraft exiting the runway. This situation produced false information 

to the pilots that resulted in operational problems. The purpose of this effort was to determine the extent, cause, and solution for 

specific operational problems resulting from these runway guard lights installed at hold lines at the Chicago O’Hare International 

Airport. 

Solutions considered include modifications to the surrounding pavement, installation modifications, raising of the fixtures, 

installation of baffles, intensity adjustments, and the flash pattern of the system. Items investigated include lighting fixture 

design, lighting fixture photometrics, installation technique and workmanship, and system flash pattern. Two information 

gathering trips were conducted at Chicago O’Hare International Airport. In addition, preliminary photometric testing of various 

manufacturers’ runway guard light fixtures were conducted at the Federal Aviation Administration’s William J. Hughes Technical 

Center. In many cases, the manufacturers were contacted or visited to discuss potential changes that could be made to modify the 

fixtures. 

It was determined that the L-852G in pavement runway guard light fixture, in its current design, will generate light that 

illuminates the pavement or the front lip in front of the fixture and that this light will be visible from the opposite side of the 

fixture. No modifications to either the pavement or fixture could be made that would eliminate this problem without sacrificing 

the intended photometric values of the fixture. The final solution to the problem at Chicago O’Hare was to reconfigure the 

system flash pattern so that it flashes in unison, thus eliminating the confusing random yellow flashing pattern that was viewed 

from the rear of the fixture. This simultaneous flash pattern maintains the intended integrity and design of the system when 

viewed from the taxiway side of the fixture. 

17. Key Words 

Runway guard lights, RGL; L-852G, Chicago O’Hare 

International Airport, ORD; In-pavement, Lighting problem 

18. Distribution Statement 

This document is available to the public through the National 

Technical Information Service (NTIS), Springfield, Virginia 

22161.

19. Security Classif. (of this report)

 Unclassified 

20. Security Classif. (of this page)

 Unclassified

21. No. of Pages

 15

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY v 

INTRODUCTION 1

Purpose 1 

Objective 1

Related Documents 1 

Background 1

DISCUSSION 4 

Fixture Design 5 

Fixture Installation 5 

Flash Configuration 6 

Federal Aviation Administration William J. Hughes Technical Center Testing 6 

Considered Solutions 7 

EVALUATION 8

TEST RESULTS 8 

CONCLUSIONS 9

LIST OF FIGURES

Figure Page 

1 Diagram of Chicago O’Hare International Airport 2 

2 View of RGL Bar From Runway Side 3 

3 Chamfer Painted Black in an Effort to Absorb and Reflect the Light Upward 4 

4 An RGL Fixture With Light Reflecting Off the Edge of the Concrete 5 

5 An RGL Fixture With Light Reflecting Off the Surface Pavement 6 

iii/iv
EXECUTIVE SUMMARY

The effort described in this technical note was accomplished in response to a request for airport 

research and development from the Office of Airport Safety and Standards, AAS-1. 

In-pavement Runway Guard Lights are a series of alternate-flashing yellow, unidirectional 

lighting fixture type (L-852G) equally spaced along a runway hold position marking that are only 

visible to aircraft approaching the hold position from the taxiway side of the fixture. In some

instances, however, problems have been encountered where pilots have reported the lights visible 

from the opposite side of the fixtures, i.e., to aircraft exiting the runway. This situation provided 

false information to pilots that resulted in operational problems. The purpose of this effort was 

to determine the extent and cause for specific operational problems resulting from these runway 

guard lights that are installed on hold lines at the Chicago O’Hare International Airport; 

specifically, pilots exiting from the runways reported seeing a considerable amount of light from

these in-pavement fixtures, so much so that they believed that they might be entering a 

construction area. 

The objective of the research was to evaluate the cause and find solutions that would eliminate 

these problems. Solutions that were considered include modifications to the surrounding 

pavement, installation modifications, raising of the fixtures, installation of baffles, intensity 

adjustments, and the flash pattern of the system. Specific items that were investigated included 

lighting fixture design, lighting fixture photometrics, installation technique and workmanship, 

and system flash pattern. To investigate these issues, two information gathering trips were

conducted at Chicago O’Hare International Airport. In addition, preliminary photometric testing 

of various manufacturers’ runway guard light fixtures were conducted at the Federal Aviation 

Administration William J. Hughes Technical Center. The manufacturers were contacted or

visited to discuss potential changes that could be made to modify the fixtures. 

It was determined that the type L-852G runway guard light fixture, in its current design, will 

generate light that illuminates the pavement or the front lip in front of the fixture and that this

light will be visible from the other side of the fixture. No modifications to either the pavement 

or fixture could be made that would eliminate this problem without sacrificing the intended 

photometric values of the fixture. The final solution to the problem at Chicago O’Hare was to

reconfigure the system flash pattern so that it flashes in unison, thus eliminating the confusing 

random yellow flashing pattern that was viewed from the rear of the fixture. This simultaneous 

flash pattern maintains the intended integrity and design of the system when viewed from the

taxiway side of the fixture. 

v/vi
INTRODUCTION

PURPOSE. 

The purpose of this investigative effort was to determine the extent and cause of operational 

problems resulting from the installation of in-pavement runway guard lights (RGL) at entrances

to runways at Chicago O’Hare International Airport (ORD). Specifically, pilots exiting from the

runways where the flashing yellow RGLs were located reported seeing considerable amounts of 

reflected light coming from the recessed fixtures, to the extent that several pilots halted short of

exiting the runway and informed air traffic control (ATC) that they were concerned about 

possibly entering a construction area. As a result of this lighting problem, a major airline carrier

lodged a formal complaint about the visible light being reflected in the runway direction, forcing 

the airport authorities to temporarily suspend operation of the in-pavement RGL. 

OBJECTIVE. 

The objective of this effort was to research and evaluate the most effective and economical

method to eliminate or redirect the reflected light associated with the in-pavement RGL systems

installed at ORD. 

RELATED DOCUMENTS. 

The following Federal Aviation Administration (FAA) advisory circulars (AC) pertain to RGL 

systems and equipment. 

• AC 150/5340-30, Design and Installation Details for Airport Visual Aids 

• AC 150/5345-46B, Specification for Runway and Taxiway Light Fixtures 

BACKGROUND. 

In 1999, ORD installed over 30 sets of in-pavement RGLs at various key locations around the 

airport surface (see figure 1). Each RGL system consists of a series of type L-852G 105-watt 

traffic yellow, in-pavement, unidirectional airport lighting fixtures. The fixtures were installed 

per the FAA AC 150/5345-28, Low-Visibility Taxiway Systems, in an effort to increase 

operational safety at the airport and reduce the possibility of runway incursions. The installation 

of the fixtures was completed in late 1999. 

Upon ORD’s activation of the in-pavement RGL system, pilots began reporting that the flashing 

yellow lights created a confusing situation. The pilots saw the RGL lights from the runway side 

and interpreted the yellow flashing lights to be those of flashing barricade lights (see figure 2). 

The pilot, believing that the taxiway was closed due to the yellow construction barricade lights, 

proceeded to the next taxiway and found the same situation. The pilot contacted ATC who 

assured the pilot that there were no barricades in that area, and it was safe to proceed. Several 

other pilots encountered the same situation, refusing to exit the runway under the assumption that 

there were barricades in the way. This problem delayed arrivals and departures and forced other 

aircraft to go around. 

1
Area of 

Evaluation 

FIGURE 1. DIAGRAM OF CHICAGO O’HARE INTERNATIONAL AIRPORT 

2
FIGURE 2. VIEW OF RGL BAR FROM RUNWAY SIDE 

Through discussions with the pilots, it was learned that the cause of the pilot’s confusion came 

from viewing the in-pavement RGL from the runway side, which gave the same appearance as 

random flashing yellow barricade lights that are typically used to identify nonaccessible 

construction areas. When viewed from the runway side, the flashing pattern of the in-pavement 

RGLs appeared to be random rather than the alternating pattern that is visible from the front of 

the in-pavement RGL, thus creating a false signal to the rear of the fixtures. 

On April 5, 2000, engineers from FAA Headquarters (HQ) and the Great Lakes Regional Office 

went to ORD to investigate the RGL problem. Experimentation by the engineers showed that 

when the in-pavement lights were set to step 2 of a 5-step regulator, the lights provided 

acceptable intensity when viewed at night from the front of the fixture while reflecting very little 

light toward the runway. Further experimentation to simulate rain conditions with standing 

water forming on the fixtures revealed that when the fixtures where submerged in water, the 

reflected light toward the runway was zero. 

FAA HQ engineers were confident that the solution of reducing the step level of the RGL

fixtures solved the problem, and offered ORD their proposed solution. ORD personnel, 

including airline representatives at ORD, were brought in to view the proposed solution of 

reducing the intensity level of the fixtures. The airline representatives rejected the solution, 

arguing that the reduction in the intensity of the fixtures would result in fixtures that do not meet 

the specifications, and the intensity would be too low for daytime use, especially in low-visibility 

conditions. It was also stated that they would not support using lower wattage lamps as a 

solution. While it may help to solve the problem, it would severely reduce the intended 

effectiveness of the fixtures. 

Being unable to resolve the reflective lighting problem, the Director of Airport Safety and 

Standards, AAS-1, requested the assistance of the Airport Technology R&D Branch, Airport 

Safety Section, AAR-411. While trying not to physically raise the fixtures so that minimal light 

3
is emitted on the pavement in front of the fixtures, FAA HQ suggested trying the following until 

a final solution was found: 

1. Chamfer the concrete lip where light strikes it to direct most of the reflected light upward 

and away from the runway. The concrete surface within this chamfer must be very

smooth to reduce any reflections. 

2. Increase the smoothness of the chamfer by applying a durable, glossy, polyurethane paint 

to the surface. 

3. Paint the chamfer black to absorb and reflect the light upward (see figure 3). 

4. Raise the fixture with spacer rings. Depending on how level the concrete is, grinding 

may also be needed. 

FIGURE 3. CHAMFER PAINTED BLACK IN AN EFFORT TO ABSORB AND 

REFLECT THE LIGHT UPWARD 

DISCUSSION

AAR-411 project personnel completed two information gathering trips to ORD to investigate the 

RGL problem and perform preliminary troubleshooting. A considerable amount of time was 

spent conducting preliminary photometric testing of various L-852G light fixtures at the William 

J. Hughes Technical Center. In addition, a significant amount of time was spent visiting or 

speaking to the manufacturers who produce the fixtures. AAR-411 project personnel, through 

visits to ORD, photometric testing, and discussions with fixture manufacturers, were able to 

identify the following key issues that were found to contribute to the problem. 

4
FIXTURE DESIGN. 

The fixtures, as produced by all major airport lighting manufacturers (Crouse-Hinds, ADB, 

Honeywell, etc.), were derived from the standard L-850 and L852 series of fixtures, and in most 

cases, the same casting as runway centerline and touchdown zone (L-850A&B) fixtures. These 

fixtures will, as determined by the William J. Hughes Technical Center testing, project a 

significant amount of light below the horizontal level because the lens are raised higher than the 

front edge of the fixture port or ramp, which projects the light to negative angles of 2 to 3 

degrees. By design, this type of fixture will always illuminate the surrounding surface in front of 

the fixture and create reflections in the reverse direction (see figure 4). 

FIGURE 4. AN RGL FIXTURE WITH LIGHT REFLECTING OFF THE 

EDGE OF THE CONCRETE 

The L-852G fixtures presently installed at ORD are provided with a single 105-watt lamp, and 

project a relatively high-intensity beam of light. This, unfortunately, also produces higherintensity reflections and may be contributing to the problem. It was determined that no matter 

which lamp wattage or brightness/intensity setting was used, it was possible that pilots would 

still confuse the RGL installation with random flashing yellow barricade lights. 

FIXTURE INSTALLATION. 

In addition to the design of the fixtures, the fixtures at ORD were installed at such a low level 

that the outer edge of the fixture, which is also at the same level as the front of the light,

impinges directly upon the vertical wall (or in some cases slope) of the saw cut hole. The 

primary reason for this low setting is to prevent the fixtures from being struck by snowplows or 

blades. This low installation creates an even more intense rearward reflection. AC 150/5340-30 

specifies that the outer edge of the fixture be level with the surrounding taxiway surface or, at 

most, a maximum of 1/16 inch (1.5 mm) below the pavement surface. Paragraph 11.1, page 75

of AC 150/5340-30 reads: 

5
“The lighting fixture must be level ±1/2 degree, and the top of the fixture edge 

must be between +0 inch (0 mm) and -1/16 inch (-1.5 mm) from the pavement

top.” 

During a site visit, these fixtures were elevated using the appropriate spacer rings to bring the 

edge of the fixture up to the same level as the concrete lip. However, by raising the fixture, the 

glare was moved from the edge of the concrete wall to the top surface of the concrete, creating a 

teardrop pattern of concentrated light on the pavement in front of the fixture (see figure 5). 

FIGURE 5. AN RGL FIXTURE WITH LIGHT REFLECTING OFF THE SURFACE 

PAVEMENT 

For another approach, a different type of inset fixture was obtained and installed. This unit, an

L-850B touchdown zone lighting fixture, provided no reduction of reflected light and, in fact, 

created a worse condition due to its higher center protrusion of approximately 3/8 inch (9.5 mm). 

Different spacer combinations, to raise the fixture closer to the level of the concrete surface,

were also tried but provided no improvement or reduction in reflected light. 

FLASH CONFIGURATION. 

Another factor that contributes to the confusing nature of the reflections generated by the inpavement RGL system is that the row of yellow lights are configured so that alternate lights are 

pulsed on and off, to provide a so-called wig-wag pattern. However, when viewed from the rear, 

the reflections can very easily be perceived as random flashing, which is the signal normally 

projected by battery powered, unsynchronized yellow construction area warning lights. 

FEDERAL AVIATION ADMINISTRATION WILLIAM J. HUGHES TECHNICAL CENTER

TESTING.

To verify that the negative angle projected light situation exists with the L-852G guard light 

fixtures, one of the units was brought back to the William J. Hughes Technical Center for testing. 

The fixture was set up, leveled, and the light-beam was projected on a vertical flat surface 10 feet 

6
(3.05 m) directly in front of the unit. A theodolite was used to measure the vertical height 

difference between the height of the outer edge of the leveled L-852G fixture and the height of 

the bottom cutoff of the light pattern projected. The cutoff point was found to be, at a distance of 

10 feet, 0.44 feet below the level of the fixture’s outer edge. These height values showed that the 

bottom edge of the L-852B unit’s projected light beam is at a negative angle of 2.52 degrees and 

will, regardless of the height at which it is installed, cause reflections rearward from either the 

vertical edge or horizontal surface of the surrounding concrete. This procedure was later 

conducted with sample fixtures from other manufacturers, and resulted in comparable

measurements of light being emitted at negative angles. 

CONSIDERED SOLUTIONS. 

Having considered the several causes for the reflections, the William J. Hughes Technical Center 

provided three possible solutions for alleviating or reducing the problem. In order of descending 

effectiveness, possible remedies offered were as follows. 

1. The specifications for the L-852G guard light fixture should be changed to contain a 

requirement that “no light shall be emitted at negative angles” to ensure a photometric or 

physical cutoff point that will prevent reflections from a correctly installed fixture. As

such, a modification will most likely involve a slight reduction in overall projected light 

intensity and a reduction in specified intensity for the +1 to +10 degree beam angles

(1000 candelas) may be required. A benefit of such a change to the advisory circular 

would be that the manufacturers would be encouraged to develop and produce L-852G 

fixtures having even lower above-pavement (top of fixture) projections than available at 

present. While this is the most effective remedy for the reflection problem, it is also the 

one that would be the most difficult, and expensive, to implement. Initial discussions 

with fixture manufacturers have shown that they may be reluctant to pursue such a 

modified fixture because of the low market demand for such fixtures. There are simply 

not enough inset RGL installations to warrant the development of a custom fixture. 

2. A change or modification to existing L-852G fixture lenses, to reduce the physical height 

of the lens and, thus, heighten the lower cutoff angle of the beam to 0 degrees, would 

significantly reduce the amount of reflection from the horizontal surface of the taxiway 

immediately in front of the fixture. Reflections from the vertical walls of the hole would 

still be a problem, however, unless the outer edge of the fixture is maintained within the 

recommended depth limit or 1/16 inch. Such modified lenses might be retrofitted to 

fixtures when they are disassembled for airport refurbishment. This too will require

physical modifications to the fixture and significantly diminish the photometric 

characteristics of the light projected from the fixture. 

3. A change to permit the use of a steady-flashing (all fixtures flash in unison) in-pavement

guard light configuration would eliminate the random flashing reflection impression that 

some pilots perceive and are confused by. A strong bold line of yellow flashing or steady 

lights, flanked by the wig-wag elevated lights on either side, should certainly be 

sufficiently attention-getting for the purpose. 

7
At the time these solutions were suggested, each of the manufacturers that produce the L-852G 

fixture was again contacted for comments. As was previously indicated, each of the 

manufacturers said they would very likely abandon the fixture as a product, as it would require 

significant development costs to design a fixture that performs as suggested. Since the overall 

reflection problem stems from both the physical design and photometric requirements of the 

L-852G fixtures, as suggested in remedy 1 and 2, it was decided that the next most easily 

implemented solution may be in finding an acceptable variation of the flash presentation. 

To investigate the possibility of varying the flash pattern, an on-site evaluation was conducted at 

ORD to determine if an alternate flash pattern would provide the desired solution. 

EVALUATION

On the evening of November 19, 2001, the original investigative team from the FAA Great 

Lakes Region and the FAA William J. Hughes Technical Center, the pilots from American

Airlines, and representatives of other interested organizations, met at ORD to conduct an 

evaluation of the following lighting configurations: 

1. Standard alternate flashing lights (wig-wag presentation) 

2. Simultaneously flashing lights (pulsing presentation) 

3. Steady-burning lights (solid line of lights) 

4. A set of randomly flashing yellow barricade lights (to provide an example of the

construction light pattern that was confused with the runway guard lights.) 

United Airlines was generous enough to provide a Chicago-based pilot and a Boeing 747-200 

aircraft to support the nighttime taxiing evaluation.

The test was accomplished on a closed runway and adjacent taxiways between the hours of 

11:00 p.m. to 1:00 a.m. A taxi route was chosen that included cockpit and port-side window

views of the three inset RGL configurations and the sample barricade light array: first from the 

back (runway/arrival) side and then from the front (taxiway/departure) side. Due to the confined 

cockpit area, the test participants had to take turns to observe the lighting from the pilot’s

viewpoint. During the test, it was most fortunate that low-visibility weather conditions of

1800-foot runway visual range in fog were encountered. This provided a most realistic, critical 

taxiing situation. 

TEST RESULTS

An informal debriefing was held on the ramp after the evaluation session, and the consensus was 

as follows. 

1. When viewed from the rear (runway) side, the appearance of the wig-wag (alternating

flashing lights) configuration was such that under certain circumstances, it might easily 

be interpreted as, or confused with, randomly flashing yellow construction or barricade 

8
lights. This would be especially true if the guard lights were viewed from the cockpit of

a smaller aircraft at short range when only a portion of the lighting array was within the

pilot’s direct field of vision. 

2. When viewed from the rear (runway) side, the appearance of the pulsing (simultaneously 

flashing) configuration was such that no sensation or perception of randomly flashing 

construction or barricade lights was noted. It was felt that this would also be true 

regardless of the aircraft size or distance from the lights. 

3. When viewed from the rear (runway) side, the appearance of the steady-burning light 

configuration, as expected, showed there could be no question or confusion with an array 

of randomly flashing barricade lights. It was noted, however, that at times the steady 

lights became lost among the numerous steady-burning taxiway and runway edge and 

centerline light fixtures. While it eliminated the flashing aspect of the problem, it did not

produce the attention-getting appearance that the in-pavement RGL system was designed

to produce. 

4. When viewed from the front (taxiway) side, all three configurations provided a bold 

indication of the holding position location. The line of steady-burning lights, however, 

was not quite as unique as the other two configurations and could, conceivably, become

immersed or rendered less effective by other nearby steady-burning yellow lights (i.e., 

runway lights on low intensity). The simultaneously flashing light configuration 

provided the bold and unique pattern required without the possibility of confusion when 

viewed from the runway side. 

CONCLUSIONS

From the results of this evaluation, and from a study of pertinent Federal Aviation 

Administration Advisory Circulars, the following conclusions were made. 

1. The L-852G lighting fixture, in its current design, will always generate light that is

directed downward towards the pavement in front of the fixture or onto the front lip of 

the fixture. No modifications are possible to eliminate this problem without sacrificing 

the intended photometric values of the fixture. A completely new fixture, with revised 

photometric requirements, would be necessary to perform as required without generating 

the downward shining light. 

2. Variations in installation technique and workmanship, while contributing to the 

backscattered lighting problem, were found not to be the primary cause of the problem. 

While attempts to vary the installation height and surface finish in front of the fixture did

show minimal reductions in the amount of reflected light, it did not solve the problem of 

the light being seen from the runway side of the fixtures. 

3. The problem was common with all manufacturers, with all types of L-852G fixtures. The 

problem could not be isolated to one vendor or one type of fixture. 

9
4. The problems encountered with the L-852G are isolated to that fixture style only. The

only other applications for the unidirectional inset lights have been as touchdown zone 

lights and stopbar lights. In this scenario, aircraft only proceed toward the lights and not

approach them from the rear where reflected light might be a consideration. Runway 

guard lights (RGL), however, are approached from either direction, resulting in a unique 

problem of reflections to the rear of the fixtures. 

5. The simultaneous flashing configuration was determined to be the most effective 

configuration because it provided the attention-getting appearance that the in-pavement

RGL system was designed to produce, and was not confused for a construction barricade 

when viewed from the runway side. 

6. The final solution to the problem encountered at Chicago O’Hare International Airport 

was to reconfigure the flash pattern of the in-pavement RGL system so that it flashes in 

unison, eliminating the confusing random yellow flashing pattern that is viewed from the 

runway side of the fixture, while still maintaining the intended integrity of the system 

when viewed from the taxiway side. 

10