Introduction

Relevant standards for road lighting (street lighting) include EN13201 and IES RP-8-21, the former being a European standard and the latter an American standard. The full name of IES RP-8-21 is “ANSI/IES RP-8-21: Lighting Roadway and Parking Facilities.” However, unlike EN13201, IES RP-8-21 covers a wide range of topics, integrating several previously independent IES standards, such as visual and basic concepts, ambient light interference, and operation/maintenance. It also focuses on lighting calculations (What’s lighting calculation?) related to road lighting, traffic flow, and lighting standards determined by road type, ultimately forming the road and parking facility lighting standards. Since EN13201 does not cover many aspects, we will mainly introduce the overlapping areas. For example, IES RP-8-21 primarily addresses road classification (highways, expressways, streets, and parking lots), highway lighting / street lighting, pedestrian activity classification, and their corresponding lighting standards. EN13201, on the other hand, addresses roads, sidewalks, conflict areas, traffic flow/composition, and their corresponding lighting standards.

Other provisions of RP-8-21

Beyond the road classification, lighting standards, and standard selection discussed in this article, RP-8-21 covers a wide range of other lighting-related knowledge. For example, Chapter 2 primarily includes fundamental knowledge of light, such as the spectrum, the structure of the human eye and basic laws of vision, units of light measurement, photometric test reports, and the classification of light distribution. Chapter 3 mainly addresses calculation methods for road lighting, specifying luminaire distribution, grid calculation, light loss factor, r-table, luminance, uniformity, and glare. Chapter 4 deals with obtrusive light, detailing light trespass (What’s light trespass?), glare, and sky glow, their hazards, and corresponding regulations. Chapter 6 covers lighting system components, including light source types, luminaire installation methods, luminaire composition (housing, LEDs, and power supply), control systems, distribution cabinets, wiring, light poles, and foundations. Chapter 9 of this standard covers information related to the maintenance and operation of lighting, introducing the necessity of maintenance, preparatory work before maintenance (Street lighting maintenance – tips and benefits), and the content of maintenance (cleaning and replacement cycle of lamps, troubleshooting of equipment failures, and monitoring of system operation), which can ensure the long-term stable operation of the lighting system. Chapters 12-19 of this standard mainly talk about lighting-related content related to roads, such as intersections, roundabouts, sidewalks, tunnels, toll stations, parking lots, roadside facilities, parking lots, and roadway signs.

Highway lighting and street lighting in RP-8-21

RP-8-21 categorizes road lighting into highway lighting and street lighting. Highway lighting refers to the illumination provided for highways, expressways, roads with limited access, and roads generally without pedestrians, cyclists, or parked vehicles. Its primary purpose is to help drivers maintain their position on highways and to aid in the detection of obstacles both within and outside the range of vehicle headlights. Here, “highway” includes expressways; a highway is a divided road with fully controlled access, while an expressway is a divided road with partially controlled access. EN13201 and related Chinese standards do not specify lighting requirements for highways (In Europa they called them expressway), which is a significant difference from RP-8-21. Street lighting in RP-8-21 refers to the illumination provided for main (arterial), collector, and local roads, which are typically used by pedestrians and cyclists at night. The primary purpose of street lighting is to help drivers identify obstacles, provide sufficient visibility for pedestrians and cyclists, and assist in visual search tasks of the street and its surrounding area. This is very similar to the EN13201 standard (More about EN13201 road lighting standard). In general, RP-8-21 subdivides roads into two categories: highways and streets. EN13201 calls them all “street” (which actually includes expressways and ordinary streets), but its “street” includes three main categories: motor vehicle lanes, non-motor vehicle lanes (sidewalk), and conflict areas.

Lighting standard differences between RP-8-21 and EN13201

Lighting criteria for highway lighting as per RP-8-21

Highway lighting is suitable for roads where there is little or no pedestrian or cyclist activity (generally referring to expressways). These roads are typically roads with limited access (i.e., highways and expressways). The RP-8-21 standard recommends using the luminance method for designing continuous lighting for highways, with lighting design standards shown in the left half of the table below. Partial lighting is sometimes used on highways and expressways. For example, isolated interchanges and ramps (the conflict zone on a highway, i.e., the area between the bifurcation point and the point on the ramp and through lanes) are designed based on illuminance rather than luminance (About luminance and illuminance). Depending on the road classification, the right half of the table below shows the recommended average sustained illuminance levels.

Highway lighting standard as per RP-8-21

Lighting criteria for street lighting as per RP-8-21

Before determining the lighting level of street lighting according to the RP-8-21 standard, we need to clarify the classification of streets and the status of pedestrian activity. This is somewhat similar to the EN13201 standard, but there are still some differences, which we will explain in detail below.

Street light classification

The following are the definitions of different streets in the RP-8-21 standard, but it is also recommended to refer to the definitions of the street management authorities. This is because the RP-8-21 standard itself provides a relatively general framework for understanding these streets, aiming to provide practitioners with a basic understanding.

Arterial streets (Main streets): Part of the road system that forms the main traffic flow network. They connect major traffic generation areas (such as city centers and transportation hubs) and major access routes in and out of the city. Sometimes they are further subdivided into primary and secondary categories; however, this distinction is not necessary for the purpose of street lighting. These routes primarily serve through traffic, and secondarily provide lighting for buildings along the street.

Collector streets: Roads that serve traffic between arterial roads and local streets. These streets are mainly used for traffic flow within residential, commercial, and industrial areas. Distribution streets are used for truck or bus traffic and provide lighting for adjacent buildings.

Local streets: Local streets primarily provide direct access to residential, commercial, industrial, or adjacent buildings. They constitute a large proportion of the street system but handle relatively low vehicular traffic.

Pedestrian activity classifications

Pedestrian activity areas are typically classified based on the intensity of pedestrian activity during nighttime hours (sometimes referred to as pedestrian traffic). The EN13201 standard also incorporates the concepts of pedestrian and vehicular traffic in its determination of street lighting levels. The logic behind using pedestrian traffic as a standard is based on the idea that higher pedestrian traffic on sidewalks indicates a greater probability of pedestrians being on the street, thus requiring higher lighting levels. Furthermore, the definition of pedestrian activity sometimes references other standards, such as land use and population density. The choice of the pedestrian activity level is an engineering judgment based on the estimated number of pedestrians typically present in an area approximately 100m long. The frequency of pedestrian activity is not constant throughout the night. Typically, the number of pedestrians in each area decreases during late night and early morning. Therefore, variations in pedestrian activity and reductions in lighting levels can be considered. This can be achieved using dimmable lighting control systems (Timer dimming in street lighting) that can adjust light intensity.

High pedestrian activity area: More than 100 pedestrians during the peak hourly traffic period at night. This includes, for example, downtown areas with dense urban development (typically exceeding 3,000 pedestrians per square kilometer) and areas surrounding large stadiums.

Medium pedestrian activity areas: 11 to 99 pedestrians during peak hourly traffic at night.

Low pedestrian activity areas: Fewer than 10 pedestrians during peak hourly traffic at night. In low activity areas, it is recommended that the jurisdiction determine whether pedestrian lighting is necessary, as lighting is generally less valuable in this application.

Street lighting standard in RP-8-21

Luminance is a design standard for street lighting. After clarifying the relevant information regarding road classification and pedestrian activity classification, we can look up the corresponding lighting class and lighting requirements for that road by referring to a table. These requirements include luminance, uniformity, and veiling luminance ratio, etc. Here, the veiling luminance ratio is something similar to Ti (more details about Ti in street lighting and GR in sports lighting). For pedestrian lighting, horizontal and vertical illuminance are design standards. If the bicycle lane is adjacent to the road (within the surrounding area), the bicycle lane lighting should meet the surrounding ratio requirements. If the bicycle lane is located within the road's ownership area but not within the surrounding area, the pedestrian horizontal illuminance standard should apply. The SR criterion should be 0.8, which is the ratio of the average illuminance of the surrounding area adjacent to the travel way (3.6 m wide) to the average illuminance of the travel lane itself. This differs significantly from the EN13201 standard. For more information on SR, please click on our corresponding blog - SR vs EIR in street lighting standard EN13201.

Street lighting standard as per RP-8-21

ZGSM street lighting solution

ZGSM has been deeply involved in the R&D, production, and sales of LED streetlights for over 20 years. Its products offer highly adaptable professional lighting solutions for various scenarios, including expressways, urban arterial roads, and rural roads. Regarding highway lighting, ZGSM's view is to provide partial lighting when necessary, primarily for complex traffic conditions such as ramps, curves, and bridges. Of course, continuous lighting can be provided for highways (expressways) where resources allow, but this is very expensive, especially in countries with highly developed highway networks like China. Below are some representative ZGSM streetlight products, please click on the images for more information.

Summary

Overall, RP-8-21 and EN 13201, as core standards representing the road lighting concepts of the Americas and Europe, differ significantly in scope, classification, and design principles. RP-8-21 is a comprehensive standard covering not only road and parking lot lighting but also delving into fundamental optics, visual theory, ambient light interference, and the maintenance of road lighting systems. One of its most notable features is the clear distinction between "highway lighting" and "street lighting," providing independent lighting standards for highways and expressways. In contrast, EN 13201 does not differentiate between expressways and streets. At the street lighting level, while both consider road classification and pedestrian activity levels, RP-8-21's road classification is more general, and its pedestrian activity levels (high, medium, low) are more vague than EN 13201, relying more on engineers' professional judgment. EN 13201, on the other hand, provides more detailed information in this area. For more information on EN 13201 road lighting, please contact ZGSM. Regarding key design metrics, RP-8-21 primarily recommends using the luminance method and introduces unique "veiling luminance ratio" and "surround ratio" to evaluate glare and ambient lighting. This differs from the "threshold increment" and "edge illuminance ratio" used in EN 13201 in both concept and calculation. Therefore, understanding these core differences is crucial for accurate, compliant, and effective lighting design (ZGSM lighting design solutions) under different standard systems.

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