Introduction

Post top lighting refers to a type of outdoor lighting fixture typically and vertically installed on poles. It is widely used in various outdoor spaces, including roadways, pathways, parks, parking lots, industrial and residential areas, which is mainly for lighting road in these areas. Post top lighting is very helpful in reducing accidents, improving nighttime activities and changing the image of cities/villages. With the changes in the world and the development of the industry, the ideal post top lighting needs to be able to cover the entire road while maintaining energy saving, which is also the goal that ZGSM has been pursuing. ZGSM believes that the two important points are high light efficiency (Check to find more details about how to improve the luminous efficacy of LED lights) and reasonable light distribution. This article will mainly explain the importance of light distribution selection for lighting, as well as the practical application of post top lights with different light distributions. Now let’s go into the text to learn more.

Asymmetrical and symmetrical light distribution

The core difference between symmetrical and asymmetrical light distribution lies in the difference in light intensity in different directions. Symmetrical light distribution takes the lamp as the center and projects evenly around to form a symmetrical light distribution pattern (circular). In Candela Table – Type C, we can see that when the γ angle is constant, the intensity of light in different c planes is the same. Asymmetric light distribution has different intensities in different projection directions, presenting an asymmetric light distribution pattern, that is, the light will be concentrated or focused in a specific direction. Symmetrical light distribution spreads evenly at 360°, forming a circular light spot on the illuminated surface, which is suitable for areas that require all-round lighting, such as parks or parking lots. Asymmetric light distribution often forms not a circular light spot on the illuminated surface, but an elliptical, long strip, semicircular, etc. light spot. For example, in the actual application of post top lighting, it needs to illuminate a long road. The circular light spot cannot effectively cover the area far away from the lamp (instead, it will shine the light to the periphery of the road – the back of the lamp), while the long strip light spot can accurately cover the road or sidewalk to avoid light waste. More details more Photometric testing – symmetric or asymmetric lighting distribution.

Benefit of asymmetrical light distribution

The core advantage of the asymmetric light distribution of post top light lies in its “precise light control” ability, which makes it have many advantages in outdoor lighting. The following ZGSM lists its three core advantages.

Accurate light distribution: We know that symmetrical light distribution often illuminates a circular area within a certain range directly below the lamp, while asymmetric light distribution is differentiated in each area under the lamp. It will focus the light on the area that needs to be illuminated, while reducing the light in the non-essential lighting area. For example, in the road lighting of the residential area, asymmetric light distribution can project most of the light emitted by the lamp to the lane, sidewalk, parking lot and crosswalk, etc., and only a small amount of light to non-essential areas including green belts, courtyards and houses, etc.

Low energy consumption and light pollution: The precise light distribution characteristics enable the post top light equipped with asymmetric distribution to achieve the desired lighting effect with lower power lamps or reduce the number of lamps. Combined with the characteristics of high light efficiency of LED, LED is very in line with the development trend of green energy saving. In addition, since the light is mainly concentrated in the area that needs to be illuminated, it can often reduce the light radiation upward or to the surrounding irrelevant areas, which helps to reduce light pollution (What’s light pollution and how to reduce it in street lighting?) to residential areas, wildlife habitats and the sky, thereby reducing the impact on residents’ lives, wildlife habitats and astronomical observations.

Reduce installation costs: Due to the asymmetric light distribution design of post top light, one lamp can often adapt to different installation conditions. Whether it is a wide road, a narrow road, a circular road, a parking area or a crosswalk, it can often meet the lighting needs with fewer lamps. In the actual installation process, the installer does not have to make too many adjustments to the projection direction of the lamp. Taking the crosswalk as an example, a post top lighting with asymmetric light distribution can illuminate the entire zebra crossing without setting up street lights on both sides like traditional street lights, which is very helpful to reduce installation costs and simplify the installation steps, including frequent adjustment of lamp positions or adding auxiliary equipment.

Post top lighting with different light distributions

Post top lighting (More ZGSM post top lights) can be equipped with traditional LED street light lenses to achieve light distributions such as type I, type II, and type III. These different light distributions allow the post top light to evenly distribute light on the road at different lamp pole heights and road widths. However, in actual applications, the road conditions can be very complicated. For example, some lamps are installed in the middle of the road, some lamps are next to houses, some roads need to illuminate crosswalks, and some lamps need to illuminate parking lots. These light distributions may be adjusted to meet the desired requirements, but this is often a time-consuming and labor-intensive process. Therefore, it is necessary to have other light distribution options so that the post top light can be better used for lighting in these areas. Below we list 4 more special scenarios and what kind of light distribution should be used for these scenarios.

Post top lighting in middle

When the post top light is installed in the middle of the road (such as a pedestrian street, square, and park), we need symmetrical light distribution so that the post top light can illuminate the road in front and behind the lamp at the same time. This type of lighting distribution emits bright light in two opposite directions, making it ideal for wide roads. Imagine if a lamp with traditional light distribution is located in the middle of the road, the light can only shine directly in front, and only a part of the light shines to the back of the lamp. The lighting effect is definitely not satisfactory. On the contrary, a post top equipped with symmetrical light distribution (axial symmetry, not central symmetry) can diffuse the light evenly to the front and back of the lamp. The following is diagram of this type of light distribution and the application scenario is shown in the figure below.

Post top lighting near house

Post top light will also be installed on roads, courtyards and some paths in residential areas. The main feature of these application places is that they do not want too much light to fall behind the lamps, because there are often houses, walls, lawns or other buildings behind these lamps. Light from the post top lighting entering the surrounding areas will cause light invasion, which will affect the lives of residents. A reasonable solution is to shield the light from the lamp facing backwards. ZGSM lamps can be equipped with light shield (house side shield) to do this. Similarly, we can equip front side shield, right side shield, left side shield to reduce the light irradiated by the lamp in a specific direction and thus reduce the impact of the lamp on non-essential lighting areas (What’s light trespass and how to reduce it?). The following is diagram of this type of light distribution and the application scenario is shown in the figure below.

Post top lighting for pedestrian crossing

Post top lights are sometimes installed near pedestrian crossings to provide necessary lighting for crosswalks. Conventional post top lights can provide lighting for the crossing, but they also disperse the light to other areas. At the same time, relevant standards also propose that the detection of pedestrians on crosswalks does not rely on traditional negative contrast (i.e., the outline formed against the bright road background), but through positive contrast to clearly show pedestrians on the sidewalk for drivers to identify. An effective solution is to use a post top lighting with asymmetric light distribution and install it on the side of the vehicle approaching the intersection, so that the light can illuminate the side of the pedestrian facing the vehicle driver. Below are two polarized designs, one of which is a right-side polarized design and the other is a left-side polarized design. Both light distributions can provide sufficient lighting and contrast in the vertical plane of the crosswalk (right or left), so that drivers can more easily find pedestrians at a longer distance. Find more details more about pedestrian lighting.

Post top lighting for parking lot

Post top lighting is often used for parking lot lighting (How to choose the proper parking lot lighting solutions?). Usually, type I, II, and III light distribution can provide reasonable lighting for parking spaces and lanes in these parking lots. But when the lamps are installed around the sides or walls of the parking lot, we often need a wider choice of lateral light distribution. This type of light distribution has strong forward-projected light, and less light will be projected to the sides or back of the site, so that the light can be concentrated inside the parking lot as much as possible, which makes them very suitable for illuminating the surrounding areas of the parking lot. The type 4 light distribution types shine in a half circle (almost no light behind light), we will get a spotlight that spreads out wider on one side. On some special roads, faster lanes (2-3 lanes, plus a parking lane), this type of light distribution also has certain application prospects. The following is diagram of this type of light distribution and the application scenario is shown in the figure below.

ZGSM post top lighting solutions

ZGSM offers modern post top lights including the Halo and L series, as well as traditional post top lights, including models 1094, 1088 and 1058. Click on the images below to view ZGSM’s different series of post top lighting solutions. In addition to the products themselves, we can customize light distributions for our customers to meet specific lighting needs. If you have any questions about how to choose a light distribution for post top lighting, please feel free to consult ZGSM.

Summary

This article mainly explains the light distribution characteristics of post top lighting. Its light distribution characteristics are no longer the traditional symmetrical light distribution, but gradually turn to asymmetrical light distribution. By comparing symmetrical light distribution and asymmetrical light distribution, we know the application advantages of asymmetrical light distribution. In addition, with the development of technology, different application scenarios also require post top light to have special light distribution to ensure that it can concentrate more light in the required lighting area in the application. These light distributions make it well suited for sidewalks, parking lots, residential roads, pedestrian streets and parks, etc. If your project includes these application scenarios and you have questions about the choice of light distribution (How to choose the right light distribution for your streetlights?), please contact us for more information.

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