The primary role of roadway lighting is to provide road users with the necessary visual conditions at night to ensure that they can travel safely and comfortably. Not only does it need to clearly display the various features of the road and traffic, such as sidewalks, lanes, road signs, road markings, crosswalks, pedestrian crossings, etc., but these features are essential for all users, including pedestrians, cyclists and motorists. Additionally, street lighting fixtures not only need to be efficient, reliable, and durable, but should also look aesthetically pleasing and harmonize with their surroundings both day and night.

Lighting design standards describe roadway lighting levels based on different categories of lighting parameters to meet local lighting needs. The selection of these levels should take into account the function of the road, traffic density, traffic complexity, traffic separation, pedestrian flow and ambient brightness. The roadway classification can be found in the EN 13201 standard.

For motorways, there are five lighting classes (M1 to M5). These levels are shown in the table below.

The recommended Maintained Average Luminance (Lav) ensures that the roadway is bright enough to show objects clearly, while the Overall Uniformity Ratio (Uo) ensures that no portion of the roadway is obscured so that it is too dark to be used as a background for objects. Longitudinal Uniformity (Ul) refers to the ratio of minimum to maximum luminance along a longitudinal line passing through the observer's position and ensures that visible visual speckles are avoided on the illuminated roadway. The glare-inhibiting (TI) limit ensures that glare does not impair the vision of road users.

Conflict Areas

Driveways are typically near or leading to utility areas such as bus terminals, ferry terminals, cab stands, toll booths, or parking lots. Other similar areas of concern include intersections, pedestrian crossings and traffic circles. These are often referred to as "conflict zones" and are better suited for lighting design using the illuminance method.

Area lighting techniques are used to illuminate open spaces, such as conflict zones in traffic mixing or traffic diversion areas. The main requirements are to provide specific illuminance levels and uniformity ratios and to control glare effectively. In these conflict zones, the visual task is usually more complex than for straight roads due to the variability of the road layout and the frequent passage of pedestrians, bicyclists or other road users. Therefore, for these areas (including intersections, traffic circles, pedestrian crossings, etc.), a higher level of lighting should be provided to ensure safety.

Sidewalk and Bikeway Lighting

Sidewalks and bikeways (without motorized vehicles, P1 through P6) are classified into five classes based on lighting levels. Unlike highways, pedestrians prefer a brighter environment for increased safety. Therefore, lighting in these areas is mainly based on illumination level as the main consideration, as shown in the table below. For areas where face recognition is required (e.g. alleyways), it is recommended that luminaires with a color rendering index greater than 70 be selected, and there are corresponding requirements for minimum vertical illuminance levels to improve safety and crime prevention.

The roadway lighting simulation design layout involves two main aspects: street layout and pole placement.

Street Layout

The street layout refers to the components that make up a roadway. In different countries or cities, there may be many variations of street layout, but it usually includes the following main elements: motorway, bicycle lanes, sidewalks, parking lanes, green belts, barrier zones, emergency lanes, separation zones, and emergency lanes. The combination of these elements forms the basic outline of a city street. Sometimes a street may include only motor vehicle lanes, sometimes it may be a combination of motor vehicle lanes and bicycle lanes, or a combination of motor vehicle lanes, separated strips, and emergency lanes, etc. Urban streets are usually a combination of these elements.

Layout of light poles

Once the lighting standards and street layout have been determined, the arrangement of the light poles should also be selected based on the roadway conditions. In addition, the distance between light poles, the height of the poles, the angle of the boom, the amount of indentation, the over-length and the length of the boom if must be confirmed before the lighting simulation is carried out. The following are five common light pole arrangements for street lighting.

Single side arrangement

Applicable to the width of the roadway does not exceed the streetlight installation height. This arrangement installs the street light on one side of the road. It has the advantage of providing good visual guidance and longitudinal uniformity on the roadway. However, one of its main disadvantages is that the luminance of the road surface on the far side must be lower than that of the road surface on the near side of the luminaire. The overall uniformity can usually be improved by proper lighting distribution design. In addition, this arrangement is also suitable for branch roads.

Double-sided staggered arrangement

This arrangement is usually used when the width of the roadway is between 1 and 1.5 times the installed height of the streetlight. This arrangement staggers or meanders the luminaires along both sides of the road. However, such an arrangement may result in alternating bright and dim areas, creating an unpleasant visual effect, and therefore requires special attention to the uniformity of brightness on the road surface. Staggered arrangements are generally not recommended for highways due to the difficulty of achieving acceptable longitudinal uniformity.

Bilateral symmetrical arrangement

The luminaires of this arrangement face each other and are mainly used in cases where the width of the road is greater than 1.5 times the installation height of the street light. It is recommended for use on spacious carriageways or highways.

Center symmetrical arrangement

The double-center arrangement is mainly used for two-lane roads. Lighting columns are located in the center median. Each lighting column usually has two luminaires mounted back-to-back on each side of the lane. This type of lighting arrangement usually requires the roadway to be equipped with wide median islands, which reduces capital and maintenance costs. For this type of lighting arrangement, we need to be aware of the potential risks that may exist during lighting maintenance due to the proximity of the divider islands to the express lanes. Therefore, it is recommended that this be done with lane closures.

Centrosymmetric and bilaterally symmetric

In the combination of centrosymmetric and bilaterally symmetric arrangements, twin luminaires located in the central reservation are combined with relative arrangements. Hard shoulders are generally provided on highways, and the lighting columns should be located on one side of the hard shoulder. In other words, in this road layout, the opposite arrangement is preferred to the centrally symmetrical arrangement. This type of arrangement is recommended for highways with particularly wide lanes.

DIALux design for road lighting simulation

Once the lighting standards, the street layout and the arrangement of the light poles have been determined, a road lighting simulation is carried out with the aid of lighting software. In this process we can import an overview of the street into DIALux, including the number of motorways, sidewalks (bike lanes), barrier strips, etc. We can also import the street layout into DIALux. Next, we can import the IES files of the luminaires. Experienced designers can use this information to quickly select the appropriate street lighting, wattage and spectrum. Finally, the design is adjusted according to specific requirements.

Basic steps of dialux road lighting simulation

Determine lighting standards (requirements)

Create street profile

Select street lighting equipment

Adjustment of the street lighting arrangement (correct placement of poles and lamps)

Calculation of the lighting parameters and adjustment of the design as required

Exporting the DIALux lighting design report

Lighting simulation is a rather complex process. If you are interested, you can check out the tutorials on the DIALux website. Furthermore, if you are still looking for the right street lighting for your project, you can refer to our lighting fixture catalog, Kinlights offers road lighting solutions. We welcome you to communicate with each other and share your experience in street lighting design and product selection. We provide 24/7 customer service!