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IESNA RP-19-01

RoadwaySign

Lighting

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IESNA RP-19-01

IESNA Recommeded Practice for Roadway Sign Lighting

Publication of this Committee Report has been approved by the IESNA. Suggestions forrevisions should be directed to the IESNA.

Prepared by:

The Sign Lighting Subcommitteeof the IESNA Roadway Lighting Committee



Copyright 2001 by the Illuminating Engineering Society of North America.

Approved by the IESNA Board of Directors, March 3, 2001, as a Transaction of the Illuminating EngineeringSociety of North America.

All rights reserved. No part of this publication may be reproduced in any form, in any electronic retrieval systemor otherwise, without prior written permission of the IESNA.

Published by the Illuminating Engineering Society of North America, 120 Wall Street, New York, New York 10005.

IESNA Standards and Guides are developed through committee consensus and produced by the IESNA Officein New York. Careful attention is given to style and accuracy. If any errors are noted in this document, please for-ward them to Rita Harrold, Director Educational and Technical Development, at the above address for verificationand correction. The IESNA welcomes and urges feedback and comments.

ISBN # 0-87995-175-3

Printed in the United States of America.



Prepared by the Sign Lighting Subcommittee of the IESNA Roadway Lighting Committee

Sign Lighting Subcommittee

Ian Lewin, Subcommittee Chair

B. AnanthanarayananJ. B. ArensR. B. ChongZ. DurysJ. A. HavardM. E. KeckL. J. Maloney

H. OdleM. OwensM. PackerR. RainierC. ShaflikG. E. SmallwoodV. H. Waight

W. AdrianY. S. Abdelsamed*P. Allegretto*B. AnanthanarayananS. W-Annoh*J. B. ArensJ. D. ArmstrongP. ArumugasaamyJ. A. BastianpillaiP. C. BoxR. A. BradfordS. Braun*M. Bucci*J. J. Buraczynski*K A. BurkettJ. C. Busser**M. G. CanavanE. Cacique*V. F. CarneyT.J. Chapman*B. T. Chau*A. P. Cheng*R B. ChongV. CiminoR. D. ClearP. ContosW. CraigL. Crawford*M. D. CrosslandW. Daiber*J. E. DegnanN. DittmannJ. M. Doyle*W. Edman**K. Fairbanks**G. A. EslingerT. Fenimore*D. H. Fox*M. FreedmanD.G. Garner

R. Gibbons*R. C. GuptaR. L. HammG. Harlow*J. M. HartG. Hauser*J. A. HavardW. A. HughesD. E. Husby*R.G. Irvine*M. S. JanoffJ. E. Jewell*R. Kauffman*M. E. Keck**D. KeithG. Keller*A. KetvirtisE. Kramer*J. Kroll*R. LeVereI. LewinL. Lewis*C.H. LochD. MaceD. R. Macha*M. MaltezosM.A. Maners, Jr.*P. G. McCarthy*J. McCormick**S. W. McKnightF. MeyersJ.J. MickelC. Miller*D. R. MonahanR. G. MonsoorW. E. Morehead*E. MorelR. Nabours*K. Negash*H. Odle

A. OerkvitzW. OkonM. Owens*P. Dalle Pezze*J.L. Pimenta*R. Rainier*P. H. Reed, Jr.*M. J. Robinson*S. RoseE.C. RowsellP. P. SabuS. Schmidt*C. Shaflik*R. N. SchwabB.L. Shelby**A.D. Silbiger*J-F. SimardR. L. SitzemaG.E. SmallwoodS. G. Spitulski*R. E. StarkR. StemprokD.C. Strong*R. Summerford*C. V. Thomas*D. TurnerH. A. Van DusenR. VincentR. P. Vogel*V. H. Waight*J.D. WatersP.C WatsonJ. WeaverS. Wegner*R. R. Wylie**A. B.York*

* Advisory Members** Honorary Members

IESNA Roadway Lighting Committee

Paul J. Lutkevich, Chair





Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

2. Classification of Lighted Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

3.Sign Light Source Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13.1 Source characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13.2 Color rendering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

4. Standardized or Regulated Sign Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

5. Elements of Roadway Sign Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25.2 Ambient Luminance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45.3 Reflectivity and contrast. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45.4 Sign Luminance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45.5 Uniformity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

6. Electrical Control Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

7. Externally Lighted Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47.1 Design levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47.2 Uniformity Ratios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47.3 Luminaire Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

7.3.1 Top Mounted Luminaires. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47.3.2 Bottom Mounted Luminaires. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57.3.3 Ground or Remote Located Luminaires. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

8. Internally Lighted Signs (Fixed Message Signs Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58.2 Design Levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58.3 Uniformity Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

9.Retroflectorization and Vehicle Forward Headlighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

10. Retroflectorization and External Sign Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

11. Maintenance of Lighted Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .611.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .611.2 Scheduled Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .611.3 Need for Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

12. Light Loss Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .612.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..612.2 Light Loss Factor (LLF). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

12.2.1 Lamp Lumen Depreciation Factor (LLD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .712.2.2 Luminaire Dirt Depreciation Factor (LDD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .712.2.3 Luminaire Ambient Temperature Factor (TF). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .712.2.4 Ballast Factor (BF). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .712.2.5 Voltage-to-Luminaire Factor (VF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .712.2.6 Manufacturing Tolerance (MT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7



Contents

13. Sign Surface Reflectance and Color Change Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

14. Sign Lighting Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9



IESNA Recommended Practice forRoadway Sign Lighting

1. INTRODUCTION

This recommended practice is a revision and expan-sion of the 1982 IESNA publication RP-19.1

These recommendations provide guidelines only for thelighting of roadway signs.They do not provide standardsfor the shape, message, letters, symbols, color, size, orlocation of roadway signs since these are covered bythe design requirements of the applicable federal regu-lations2 and the appropriate highway agencies.

This document does not address the requirements forchangeable message signs.

Additional practical applications regarding non-high-way signs may be found in Chapter 17 of the IESNAHandbook, 9th Edition, 2000.3

This document is intended to supplement and not tosupersede the regulations and requirements of anyfederal, state, provincial, regional or local governmentagency.

A sign that is designed to be legible under daylightconditions can also be lighted to fulfill its basic pur-pose at night. Well-designed sign lighting can aid thedriver in rapid, accurate recognition and understand-ing of the sign’s message. This serves to improvesafety by reducing the possibility that motorists willstop or drastically reduce speed at signs that may oth-erwise be difficult to read. Where the background,against which a sign is to be seen, has a high level of(ambient) luminance, sign lighting can provide thesign legibility necessary for decisive driver action.

Lighting of roadway signs becomes more significant as(1) volume of traffic increases, (2) complexity of highwaydesign increases, (3) adverse weather in specific loca-tions is prevalent, and (4) ambient luminance increases.

The lighting of retro-reflective signs is beneficial whensuch retroflectorization (formerly retro-reflectorization)alone cannot adequately convey the sign message. Itbecomes important to provide light where frequentand severe conditions of condensate, frost, dirt on asign panel, or sign face wear reduce the effectivenessof the reflective materials. During some inclementweather conditions, headlamps covered with dirt maybe ineffective in illuminating retro-reflective signs.

Ground-mounted signs should be lighted where thereis a need to attract special attention to upcoming traf-

fic patterns, such as where the approach to a roadwayconfiguration is of complex geometric design.

Traffic signs mounted on overhead structures shouldbe lighted for adequate nighttime conspicuity and leg-ibility of the sign message for several reasons:

(1) Retroflectorization alone may not provide sufficientadvance sign legibility due to the design of vehicleheadlighting systems, (i.e., the projection of themain beams downward), and the vertical and hor-izontal alignments of the roadways at theapproach to the sign.

(2) Roadway lighting is not intended to properly acti-vate or light overhead retro-reflective signs.However, careful placement of roadway luminairesin advance of an overhead sign location will pro-vide some beneficial sign illumination in the eventthat the actual sign lighting is out of service.Roadway luminaires should be placed with careso as not to cause a distracting shadow on thepavement and a significant reduction in the pave-ment lighting level because of the sign.

(3) Sight distance for sign recognition is increasedwhen signs are illuminated.

2. CLASSIFICATION OF LIGHTED SIGNS

Signs for this recommended practice are classifiedinto two categories:

(a) Externally lighted signs - signs on which a fixed mes-sage is illuminated by an external source of light.

(b)Internally lighted signs - signs in which the sourceof light is enclosed within the sign and the mes-sage becomes understandable because of thevarying transmittance of the sign face.

3. SIGN LIGHT SOURCE SELECTION

3.1 Source characteristics.Several different light sources are used to light roadwaysigns. Each light source has specific characteristics,which may make it more appropriate than others for agiven application. Energy consumption is a major con-sideration in each application, and must be balancedby other factors such as color rendering, temperature ofoperation (e.g., fluorescent lamps operating at lowambient temperature), and ease of maintenance.

1

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