Road lighting is a critical component of urban infrastructure. Its design and evaluation must adhere to a set of calculation metrics and international standards to ensure traffic safety, efficiency, pedestrian comfort, and energy efficiency.Road lighting standards aim to provide a safe, efficient, and comfortable visual environment. Major international road lighting standard systems include those from the International Commission on Illumination (CIE), European Standards (EN), and the Illuminating Engineering Society of North America (IESNA).
In order to ensure the scientific and standardized design, it is necessary to follow the road lighting standards developed by different countries and regions, such as ANSI-IES RP-8-18, CIE 140-2000, BSEN 13201-3:2015, etc.Different standards differ in terms of observation point location, occlusion luminance calculation, and target comparison modeling
Introduction to mainstream roadway lighting standards:
ANSI/IES RP-8-18 (U.S.A.): mainstream North American standards with comprehensive indicators;
CIE 140:2019 & CIE TN-007:2017 (International Commission on Illumination): emphasizes brightness, uniformity & intermediate visual perception;
BSEN 13201-3:2015 (Europe): focusing on the introduction of half-column illuminance, ambient illuminance and other human factors lighting indicators;
ABNT NBR5101-2012 (Brazil): regional national standard;
AS/NZS 1158.3.1:2020 (Australia and New Zealand): applicable to local urban and community roadway design;
IES RP-18 (U.S. Tunnel Lighting): dedicated to tunnel environments.
Comparison of computational metrics supported by each standard
Definition of main calculation indicators
- Average luminance (Lavg) unit: cd/m² refers to the average luminance of the road surface observed from the driver's viewpoint, which is an important indicator for judging the visual clarity of the road surface. Its calculation is affected by the reflective properties of the road surface, observation angle, lamps and lanterns light distribution and other factors.
- average illuminance (Eavg) and minimum illuminance (Emin) unit: lux indicates the intensity of light flux received per unit area. The average illuminance reflects the overall lighting level, the minimum illuminance is used to assess the uniformity of light, the ratio of the two (Eavg/Emin) reflects visual comfort and safety.
- Veiling Luminance (Lv) unit: cd/m² refers to the additional luminance caused by lamps or strong light sources caused by intraocular scattering, which will interfere with the observer's recognition of the target, and too high a value of Lv will increase the visual burden.
- Light Curtain Luminance Ratio (Lv/Lavg) measures the relative value of shading luminance to the average roadway luminance, and is one of the core parameters for evaluating the glare control capability of roadway lighting.
- Small Target Visibility (STV) indicates the degree of visibility of small targets (e.g., falling rocks, animals, etc.) observed under road lighting conditions. STV combines the parameters of target contrast, background luminance, and occlusion luminance, with higher values indicating that the target is easier to identify.
- Vertical illuminance (Ev) unit: lux refers to the light intensity received on a vertical surface (such as pedestrians or the front of the body), usually measured at an observation height of 1.5m, is a key indicator of pedestrian safety and facial recognition capabilities.
- semi-cylindrical illuminance (Esc) unit: lux simulation of human chest height (about 1.5m) of the half-cylindrical surface of the light intensity received for a comprehensive assessment of the pedestrian in the three-dimensional space of the light effect, is one of the indicators recommended by the EU standard.
- hemispherical illuminance (Ehs) unit: lux refers to the virtual hemisphere (usually 1.5m for the centre of the height) on the average illuminance of the light in all directions, which can comprehensively reflect the quality of the spatial light environment, is commonly used in the plaza, pavements, and other open space light assessment.
- Surround Illuminance (EA) unit: lux indicates the average illuminance in a certain range around the task lighting area (such as the edge area or background area), which is used to assess the brightness balance between the visual task area and the background. Reasonable ambient illuminance helps to reduce visual fatigue and enhance the sense of safety and spatial recognition.
- Threshold Increment (TI) in % indicates the degree of decrease in contrast between the target and the background due to the interference of glare; the larger the TI, the more severe the glare and the higher the difficulty in target recognition, which is often used as an alternative to the Lv/Lavg indicator in the CIE and BSEN standards.
- Mesopic Luminance (Lmes) unit: cd/m² is used in low-light environments to combine the response of optic rod cells (dark vision) and optic cone cells (bright vision) to calculate the integrated luminance value. The algorithm is closer to the real perception of the human eye at night.
Key differences among international standards
ANSI-IES RP-8-18 (with tunnel lighting RP-22)
- Observer position: 83.07 meters from the calculation point, line of sight 1 degree below horizontal, height 1.45 meters.
- Calculation of light curtain luminance: no axis of sight (LOS) filtering, only one direction of traffic is considered.
- STV calculation: positive and negative contrast targets are considered, emphasizing overall visibility.
CIE 140-2019 (applies to CIE 115-2010)
- Observer position: distance of 60 m, in the center of the lane or 1/4 road width from the curb.
- Masking luminance: default filtering of the center field of view 0.1-1.5° and the area more than 60° out of the line of sight.
- Glare Indicator: uses “Threshold Increment (TI)”, which indicates the percentage increase in the recognition threshold due to glare.
CIE TN 007-2017 (addition of intermediate visual luminance)
- Adding **Mesopic Luminance** calculation on the basis of CIE 140, based on the formula of CIE 191:2010, and adjusting the adaptation level of the human eye according to the actual average luminance.
BSEN 13201-3:2015
- New vertical, semi-cylindrical and hemispherical illuminance and many other indicators are added for modeling the visibility of drivers and pedestrians in different directions.
- Observer position: consistent with CIE, Lv default does not filter out light sources in the line of sight direction.
- Glare Calculation: In conjunction with CIE 146-2002 method, it is possible to manually select whether to filter out in-line-of-sight luminaires or not.
ABNT NBR5101-2012 (Brazilian Standard)
- Essentially the same as the CIE methodology, but with more emphasis on the role of semi-cylindrical illuminance in enhancing visibility of pedestrian-driver interactions.
Lv and TI calculation logic is similar to BSEN.
The calculation indexes of the above standards do not take into account the influence of daylight exposure, but some standards will take into account the influence of the road surface brought by wet weather, and there will be a different reflectance between dry road surface and wet road surface.
The reflective properties of pavement surfaces have a significant impact on illuminance calculation, luminance distribution and energy-saving design. For this reason, the industry has developed standardized reflectance tables (R-Tables) to describe the reflectance properties of pavement surfaces based on the physical surface characteristics of different pavement materials.
The most central parameter in the R table is Q₀, which represents the average reflection coefficient of this pavement under standard lighting conditions and is converted to overall reflectance by the following formula:
Overall reflectance = Q₀ × π
The higher the Q₀, the stronger the overall reflectivity of the pavement to light, and the choice of the Q₀ value directly affects the illuminance simulation results.
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