Standards for Setting the Elevation Angle of Street Lights

1. Introduction​
   Street lighting plays a crucial role in ensuring the safety and functionality of urban and rural roads. Among the various parameters in street light design, the elevation angle of the street light is a key factor that significantly impacts the lighting effect. Properly setting the elevation angle can enhance road illumination, reduce glare, and improve energy efficiency. This article delves into the norms and considerations regarding the setting of street light elevation angles.

2. Importance of the Elevation Angle​
2.1 Lighting Coverage​
   The elevation angle determines the direction and extent of light projection. A well - set elevation angle can ensure that the light evenly covers the road surface, including the carriageway, sidewalks, and intersections. For example, in a narrow street, a relatively small elevation angle might be sufficient to direct light onto the entire width of the road. In contrast, for a wide boulevard, a slightly larger elevation angle may be needed to reach the far - side lanes effectively.

2.2 Glare Control​
   Glare is a major concern in street lighting as it can cause visual discomfort and reduce driver visibility. An inappropriate elevation angle can lead to excessive upward or lateral light emission, creating glare for road users. By setting the elevation angle within an appropriate range, the light can be directed more towards the road surface, minimizing glare and improving the overall visual environment.

2.3 Energy Efficiency​
   When the elevation angle is optimized, the light is concentrated where it is needed most - on the road. This reduces light wastage in non - essential areas such as the sky or adjacent buildings. As a result, energy consumption can be decreased while maintaining adequate lighting levels, contributing to sustainable urban development.

3. Factors Affecting the Setting of the Elevation Angle​
3.1 Road Width​
   The width of the road is a fundamental factor. Narrow roads (e.g., residential streets with widths of 5 - 8 meters) typically require a smaller elevation angle. A common range for such roads might be 0 - 5 degrees. This allows the light to spread horizontally across the road without over - illuminating the adjacent areas. For wider roads, such as multi - lane highways with widths of 20 - 30 meters or more, an elevation angle in the range of 5 - 15 degrees may be more suitable. The larger angle helps to project light to the far - side lanes and shoulders.

3.2 Lamp Type and Distribution​
   Different lamp types have different light distribution characteristics. For example, cut - off luminaires are designed to direct light mainly downwards. The elevation angle for cut - off luminaires is usually set to ensure that the maximum light intensity is focused on the road surface within a certain range. In contrast, semi - cut - off luminaires have a wider light distribution, and their elevation angle setting needs to balance the need for horizontal and vertical light projection. The maximum light intensity angles for cut - off and semi - cut - off luminaires are specified in relevant standards. For cut - off luminaires, the angle between the direction of the maximum light intensity and the downward vertical axis is between 0° - 65°, and at 90° and 80°, the maximum permissible light intensities are 10 cd/1000 lm and 30 cd/1000 lm respectively. For semi - cut - off luminaires, this angle range is 0° - 75°, with maximum permissible light intensities of 50 cd/1000 lm and 100 cd/1000 lm at 90° and 80° respectively.

3.3 Surrounding Environment​
   The surrounding environment, such as the presence of buildings, trees, or other obstacles, also affects the elevation angle setting. In urban areas with tall buildings, the elevation angle may need to be adjusted to avoid light being blocked by buildings and to ensure that the light reaches the road surface. If there are trees along the road, the elevation angle should be set to minimize light absorption by the foliage and to maximize the light reaching the ground. In areas with open landscapes, such as rural roads, the elevation angle can be set more freely based on the road width and lighting requirements.

4. General Standards for Setting the Elevation Angle​
4.1 Maximum Angle Limit​
   In general, the elevation angle of street lights should not exceed 15 degrees. An elevation angle greater than 15 degrees can lead to several problems. Firstly, it reduces the luminous efficiency of the lamp as more light is directed upwards rather than onto the road surface. Secondly, it increases the risk of glare for road users, which can be particularly dangerous for drivers. Thirdly, it may cause light pollution in the surrounding areas.

4.2 Consistency within a Street​
   For a particular street, the elevation angle of all street lights should be consistent. This ensures a uniform lighting effect along the entire length of the road. Inconsistent elevation angles can create patches of uneven illumination, which may be confusing or even dangerous for road users. When installing street lights, careful attention should be paid to adjust the elevation angle of each lamp to the same value.​

4.3 Adjustment Based on Lamp Mounting Height​
   The mounting height of the street light also influences the elevation angle. For lower - mounted street lights (e.g., those with a height of 3 - 5 meters, often used in residential areas or pedestrian paths), a relatively smaller elevation angle is appropriate. This is because the light source is closer to the ground, and a small angle can still achieve sufficient horizontal light spread. As the mounting height increases (e.g., for high - mast lighting with pole heights of 20 meters or more), a slightly larger elevation angle may be required to project light over a larger area. However, even for high - mast lighting, the elevation angle should still be within the general limit of 15 degrees.

5. Special Considerations​
5.1 Intersection Lighting​
   At intersections, the elevation angle of street lights needs to be carefully adjusted to ensure comprehensive lighting. The lights should be able to illuminate all directions of the intersection, including the cross - roads and turning lanes. In some cases, additional lights or different elevation angle settings may be required compared to straight sections of the road. For example, lights at the corners of intersections may have a slightly larger elevation angle to direct light diagonally across the intersection.​

5.2 Area - specific Requirements​
   Certain areas, such as industrial zones, may have different lighting requirements. In industrial zones, where large - scale vehicles and heavy machinery operate, the lighting needs to be bright and cover a wide area. The elevation angle may be set to provide maximum horizontal and vertical light distribution to ensure the safety of workers and the proper functioning of machinery. In contrast, in historical or scenic areas, the elevation angle may be adjusted to minimize light impact on the surrounding environment and to preserve the aesthetic value of the area.

6. Conclusion​
   The setting of the elevation angle of street lights is a complex yet essential aspect of street lighting design. By considering factors such as road width, lamp type, and the surrounding environment, and adhering to general standards such as the 15 - degree maximum angle limit and consistency within a street, optimal lighting performance can be achieved. This not only improves road safety but also promotes energy efficiency and reduces light pollution. In the future, with the continuous development of lighting technology and urban planning, the standards and methods for setting street light elevation angles will continue to be refined to meet the evolving needs of society.