Key Factors to Consider in the Street Lighting Design
The main purpose of street lighting is to provide an appropriate lighting level for motorists to ensure safety in driving or for pedestrians to ensure safety while walking. In cities, street lighting plays an additional role in creating a more attractive and safer environment. The ability of street lighting to illuminate objects is affected by the quality of the light and other physical factors such as traffic levels and road surfaces. A good street lighting system will ensure the visual detection of objects at greater distances.
For more and more outdoor LED lighting projects, ZGSM’s LED street light developers have launched street lighting designs to provide customers with more comprehensive technical support. The lighting effect and overall quantity can better communicate with the end customer and calculate the project cost more accurately. At the same time, it also displays detailed street lighting data for customers, which can meet the different lighting requirements of customers. This article will describe the various lighting factors that we should consider when designing an effective lighting system, as well as the minimum standards that need to be met to ensure safe driving conditions.
Main factors which we should pay attention to?
Street lighting evaluation indicators include average road luminance Lav (road average illuminance, road minimum illuminance), brightness uniformity, longitudinal uniformity, glare, environmental ratio SR, Color Rendering Index, and visual inducement. So these are the points we need to pay attention to when doing street lighting design.
Average Road Luminance Lav in Cd/m
Road Luminance is a measure of the visibility of the road. It is the most important factor affecting whether the obstacle can be seen, and it is based on the principle of illuminating the road enough to see the outline of the obstacle. Brightness (Road Luminance) depends on the light distribution of the luminaire, the lumen output of the luminaire, the installation design of the street lighting, and the reflective properties of the road surface. The higher the brightness level, the better the lighting effect. According to lighting-class standards, Lav is in the range between 0.3 and 2.0 Cd/m2.
Uniformity is an index to measure the uniformity of light distribution on the road, which can be expressed as overall uniformity (U0) and longitudinal uniformity (UI).
Street lighting facilities must determine the allowable difference between the minimum brightness and the average brightness on the road, that is, the overall brightness uniformity, which is defined as the ratio of the minimum brightness to the average brightness on the road. Good overall uniformity ensures that all points and objects on the road are sufficiently illuminated for the driver to see. The Uo value accepted by the road lighting industry is 0.40.
On the other hand, for comfort, the difference in brightness between the brightest and darkest areas along the centerline of the lane, ie, longitudinal uniformity, should be limited. Good longitudinal uniformity reduces the pattern of high and low brightness on the road (i.e. the zebra effect), thus ensuring comfortable driving conditions. It is applicable to long and continuous roads.
Glare is the blinding sensation that occurs when the brightness of light exceeds the level of adaptation of the human eye to light. It can cause discomfort and reduce road visibility. It is measured in Threshold Increment (TI), which is the percentage increase in brightness required to compensate for the effects of glare (ie, to make the road equally visible without glare). The industry standard for the glare in street lighting is between 10% and 20%.
Road Average Illuminance, Road Minimum Illuminance, and Vertical Illuminance
The average value of the illuminance of each point is measured or calculated at the preset points on the road according to the relevant regulations of CIE. The lighting requirements of motor vehicle lanes are generally based on brightness, but the lighting requirements of sidewalks are mainly based on road illuminance. It depends on the light distribution of the lamps, the lumen output of the lamps, and the installation design of the street lighting, but it has little to do with the reflection characteristics of the road. Illuminance uniformity UE (Lmin/Lav) also needs attention in sidewalk lighting, it is the ratio of the minimum illuminance to the average illuminance on the road. To provide for uniformity the actual value of the maintained average illuminance may not exceed 1.5 times the value indicated for the class.
Surround ratio (SR)
The ratio of the average horizontal illuminance in the 5 meters wide area outside the roadway to the average horizontal illuminance on the adjacent 5 meters wide roadway. Road lighting should not only illuminate the road, but also the adjacent area so that motorists can see surrounding objects and anticipate possible road obstacles (eg, pedestrians about to step onto the road). SR is the visibility of the road perimeter relative to the main road itself. According to lighting industry standards, the SR should be at least 0.50, as this is ideal and sufficient for proper eye accommodation.
Color Rendering Index
The color rendering index measures the ability of artificial light sources to display or reproduce the color of the road or objects on the road relative to natural light sources. The natural light source (sun) has a CRI of 100. The higher the index, the better the visibility. It’s recommended CRI ≥ 70 for all types of road lighting classes.
Through the guidance auxiliary facilities of the road, such as the centerline of the road, the curb, the road sign, the emergency road barrier, etc., the driver can make the driver know his position and the direction in front of the road.
Which standard your projects shall meet?
They have different standards for vehicle lanes and sidewalks. We have listed two tables below for you to quickly check relative standards. The tables below are for motorways and sidewalks, respectively. As you can see, it includes Lav (Eav, Emin), Uo, UI, Ti, and SR requirements. Of course, in addition to lighting class M and class P, there are other lighting classes. For example, lighting-class C is for conflict areas. Normally projects or tenders have a requirement on the protection class of lamps. They will ask for either Class I or Class II for AC input LED street lights. For what is Class I or Class II, you can read our related article “Class I vs Class II vs Class III, or Class 1 vs Class 2“
Street lighting standard table
Lighting class standard table for motorways
|Lighting class||Dry-Lav in cd/m2||Dry-Uo||Dry-UI||Wet-Uo||TI in %||SR|
Lighting class standard table for pedestrians
|Lighting class||Average horizontal illuminance Eav in lx||Minimum horizontal illuminance Emin in lx||TI in %||Minimum vertical illuminance|
Ev,min in lx
|Minimum semi- cylindrical illuminance
Esc,min in lx
What lighting-class do you need to meet for your project? If you’re still hesitating, we think you can find your answer in two ways.
Requirement from tender
As a municipal project, road lighting generally has technical specifications for their lighting projects. For example, the following table is the lighting performance that our project in Kuwait requires. It gives the width of the road, the height of the pole, the length of the arm, and the tilt angle, through which we can confirm the selection of LED street lights, including wattage, lens, and pole spacing.
Generally speaking, the smaller the wattage, the larger the distance between the lamps (the fewer lamps required for the project), and the better it can meet the requirements of the project party. Of course, the price of lamps is also a factor that the project party often considers. For details, please refer to our article about street light cost.
Requirement as per lighting-class selection table
In addition, to get the requirements from the tender, you can also decide which lighting-class your road should conform to by using the factors in the selection table below. For lighting-class M, these parameters include speed, traffic volume, traffic composition, separation of carriageways, junction density, parked vehicles, ambient luminance, and navigational task. For lighting-class P, these parameters include design speed, use intensity, traffic composition, parked vehicles, ambient luminance, and facial recognition.
Because there are so many related factors, here we only discuss design speed. For example, for design speed, there are five options given across the different lighting classes M and P. The option ‘very high’ (e.g. more than 100 km/h) would apply to motorways (lighting classes M). The option ‘high’ (e.g. between 70 km/h and 100 km/h) would apply primarily to inter-urban single and dual carriageways, but also to urban principal roads between primary destinations (lighting classes M). In urban areas speed limits are 50 km/h on average, ranging from 30 km/h to 70 km/h (e.g. on major distributor roads). The option ‘moderate’ is related to this speed (lighting classes M). In residential areas with or without geometric measures for traffic calming in many cases, the speed limit is set to 30 km/h or less. Here the option ‘low’ would be the appropriate choice (lighting classes P). For areas where pedestrians are considered as main users the speed option ‘very low’, i.e. walking speed, often limited between 5 km/h and 7 km/h, here ‘very low’ should be applied (lighting classes P). If you know how to choose other factors, you can contact us or refer to the EN13201 standard or contact us to learn more.
|Parameter||Options||Weighting Value||WV selected|
|Design Speed||Very high||2||1|
|Traffic composition||Mixed with high percentage of non-motorized||2||1|
|Separation of carriageway||No||1||1|
|Navigational task||Very difficult||2||1|
|Sum of Weighting Values||SWV=4|
The number of lighting-class M = 6-SWV= M2, then you can choose lighting-class M2 as the requirement for your project.
|Parameter||Options||Weighting Value||WV selected|
|Very low (walking speed)||0|
|Traffic composition||Pedestrians, cyclists and motorized traffic||2||1|
|Pedestrians and motorized traffic||1|
|Pedestrians and cyclists only||1|
|Facial recognition||Necessary||Additional requirements||0|
|Not necessary||No additional requirements|
|Additional requirements||SWV= 2|
The number of lighting-class M = 6-SWV= P4, then you can choose lighting-class P4 as the requirement for your project.
Others which we should pay attention to
Physical factors can either enhance or detract from the performance of the road light, so it is imperative to give these factors ample consideration when creating a lighting system.
Light poles should be strong enough to carry and support light fixtures and should be the appropriate height and spacing for optimal lighting. When planning the street lighting layout, structures that obstruct traffic, such as trees, should also be considered. The following table shows several common road conditions, as well as the corresponding pole height, pole spacing, and boom.
Reference standards of the layout of poles
|No||Luminaire Category||Bracket||Poles Arrangement and Clearance||Carriageway|
|Type(layout of poles)||Outreach (m)||Clearance from the road (m)||Mounting Height (m)||Spacing (m)||Median Width (m)||Type||lanes||Width (m)|
|1||A1||Single sided||0.5||Single Sided, 1||5||24||-||Single||2||6|
|2||A2||Single sided||1.5||Single Sided, 2.75||8||30 - 35||-||Single||2||6|
|3||A2||Double T-Shape (poles on median)||1.5||Central Verge Position (symmetrically)||8||30 - 35||2||Double||1||7 each|
|4||A3||Single sided||0.5-1.5||Single Sided, 2.75||10||35 – 40||-||Single||2||7.5|
|5||A3||Double T-Shape (poles on median)||0.5-1.5||Central Verge Position (symmetrically)||10||35 – 40||4||Double||2||7.5 each|
|6||A3||Double row, opposing Pole||0.5-1.5||Double row, opposing Pole, 1||10||35-40||1-2||Single||3||10.5 each|
|7||A4||Single sided||0.5||Single Sided, 2.75||12||40 – 45||-||Single||2||7.5|
|8||A4||Double T-Shape (poles on median)||0.5||Central Verge Position (symmetrically)||12||40 – 45||6||Double||2||7.5 each|
|9||A4||Single sided||0.5||Single Sided, 2.75||14||45 – 50||-||Single||2||7.5|
|10||A4||Double U-Shape (poles on median)||0.5||Central Verge Position (symmetrically)||14||45 – 50||-||Double||3||-|
Regarding the layout of the poles, please check the below diagram.
Smart control systems are infrastructure communication systems that allow instantaneous control of lighting systems. They can automatically adjust lighting levels according to their surroundings. Studies have shown that LED street lights combined with intelligent street lighting control systems can maximize the lifespan of lamps, minimize maintenance costs, and save up to 80% in energy. Of course, the adjusted brightness also needs to meet the corresponding lighting requirements. For example, for a road that needs to meet the M3 requirements, when there are few vehicles at midnight, the illuminance requirements may be reduced by M5. Refer to the table of Lighting Class M, then the brightness of our lamps can be adjusted to 50% of the initial brightness. This not only saves power consumption but also meets the corresponding lighting needs.
Street lighting design reference
When we have clear the points that need to be paid attention to in road lighting, let’s go back to how to plan our project to meet the requirements of the project, we think Dialux is a good means. Assume that a two-way six-lane road lighting simulation needs to be made, the object lane is separated by a middle partition island, and high-pole street lights are arranged on both sides of the road. Motorways and pedestrian paths are divided by lawns. Set up street lighting on the lawn to illuminate motor vehicle roads and sidewalks.
Through the table, we choose the scheme of installing street lights on the opposite side of A3, setting the width of the two-way eight lanes to be 28 meters in total, and the width of the middle separation island to be 1 meter. The width of the lawn is 1 meter, a total of 2 meters. The width of the pedestrian path is 2 meters, a total of 4 meters. The motor vehicle lane is 3.5 meters, a total of 21 meters. The layout of the road and street lights is as below.
And we used our Rifle series 100W street light with 15500lm and T2M53007 lens. Meanwhile, the space is 40m and the lighting simulation calculation results are as follows
|Calculation Field List||Standard: EN 13201|
|Valuation Field Roadway||(All lighting performance requirements are met.)|
|Selected Lighting Class: ME3a||Lav [cd/m²]||U0||Ul||TI [%]||SR|
|Required values according to class:||≥ 1.00||≥ 0.40||≥ 0.70||≤ 15||≥ 0.50|
Street lighting project reference
ZGSM has 17 years of experience in street lamp production. Our company’s products have served more than 3,000 customers around the world. There are countless street lighting projects, large and small. We are proud to share our successful road lighting project with you here. The image below is an urban street lighting project for our Croatian client. The project was completed in 2015, and the customer chose our classic H series modular street light with an installation height of 6M to replace the original 250W metal halide light after street lighting design. At first, the customer thought that at least 100W LED lamps were needed to meet their lighting requirements. Through communication with customers, we confirmed the corresponding requirements and road conditions. Finally, with the help of the Dialux lighting simulation, we replaced the original lamps with 65W H series street lamps. The lighting effect after installation is very good, the measured ground lux value is 30% higher than that before the renovation, and the energy-saving rate reaches 70%. ZGSM is very happy that the customer’s needs have been perfectly solved, and thanks to the street lighting design team of ZGSM for giving reasonable suggestions.
The main function of public lighting is to ensure the safety of road users and enhance urban safety. Public lighting installations should be designed to provide appropriate lighting in an energy-efficient and environmentally friendly manner. This article introduces the important concerns of road simulation, different lighting levels, and how to choose the appropriate level for your project. I hope these will give you a certain understanding of road lighting simulation. If you have a project in hand, you might as well start a lighting simulation now and choose the right LED street light for your project. Of course, if you need our help, we are also very happy to provide and share the corresponding knowledge with you. Let’s get in touch.