Discussion on Urban Road Lighting Design
March 25, 2023
With the continuous acceleration of urban construction, the scale and quantity of urban roads, which are necessary conditions for urban economic development, are increasing dramatically. With the development of the lighting industry, the quality of urban lighting is getting higher and higher. The design of road lighting should not only meet the requirements of quantity and quality of lighting, but also consider the convenience of maintenance and management, safe and reliable operation, economy and energy saving, green environmental protection, etc. Many other factors. 1. Urban road lighting design steps
1. Clear road conditions
The road conditions mentioned in the urban road lighting design include the road itself, the surrounding environment of the road and the road traffic conditions, which directly affect the determination of the design standard values in the following steps. For example, the speed of motor vehicles is different, and the paving material of the road surface is different, which directly affects the difference in the corresponding illuminance value. Only with a comprehensive understanding of the road conditions can the correct design be made. 2. According to the road conditions, determine the road grade and design standards
At present, my country's urban roads are divided into five levels according to expressways, main roads, secondary arterial roads, branch roads and residential roads. The following are the standard lighting values for roads. This is the standard and foundation of urban road lighting design. The average brightness of the road surface is the most important indicator to determine whether obstacles on the road can be seen. However, most areas currently use the standard of illuminance as the benchmark for measurement. Although establishing standards based on luminance is more scientific and reasonable than establishing standards based on illuminance, the measurement of luminance is time-consuming and laborious, while the measurement of illuminance is relatively much simpler. The longitudinal uniformity of road surface brightness in the table is also one of the important parameters. Its importance lies in the driver`s driving on the road. In addition to ensuring the recognition rate of obstacles on the road, the driver`s physical and mental feelings must also be considered during long-term driving. If the longitudinal uniformity of brightness is too small, it will lead to obvious changes in brightness and darkness. "Zebra effect", the driver's repeated light and dark changes in the process of driving will make the driver irritable and endanger traffic safety. 3. Choose the lighting method
Generally, the way of road lighting can be divided into two types: conventional lighting and high pole lighting. Conventional lighting has the following layout methods: single-side layout, double-side staggered layout, bilateral symmetrical layout, central symmetrical layout and horizontal suspension cable layout. The advantage of one-sided arrangement is that it has good inductivity, but it has the problem that the brightness of the road surface on the side without lamps will be significantly lower than that on the other side, resulting in different lighting conditions for vehicles traveling in two directions. The advantage of the double-sided staggered arrangement is that the overall brightness uniformity is better than that of the single-sided arrangement, but the longitudinal uniformity of the brightness is generally poor, and the inductance is not as good as that of the single-sided arrangement. The overall uniformity of the road surface brightness and the longitudinal uniformity of the road surface brightness with two-way symmetrical layout are better. This arrangement is suitable for double-width roads with a middle divider belt, and the light efficiency is higher than that of the two-way symmetrical arrangement, and the induction is also better. The installation height of lamps in the horizontal suspension cable arrangement is generally relatively low, and the suspended lamps are easy to swing or rotate, so it is easy to cause intermittent flickering glare to the driver. Therefore, this arrangement is generally not recommended. High pole lighting is mainly used for large-area lighting, such as road interchanges, plane intersections, squares, parking lots and other places. After understanding the various characteristics of the lighting arrangement, determine the lighting arrangement method according to the needs of the construction party and the characteristics of the road itself. 4. Select the light source and lights
The light sources used for road lighting include high-pressure sodium lamps, high-pressure mercury lamps, metal halide lamps, and LED light sources. High-pressure sodium lamps have the characteristics of long life, high luminous efficiency, stable quality, various specifications and types, and good fog penetration. Metal halide lamps have high efficiency, long life, good color rendering, and can be made into light sources of various light colors and sizes, so they also occupy a place in road lighting. At present, they are mainly used in those who are sensitive to color rendering and light color Roads with higher demands. The main advantages of high-pressure mercury lamps are good fog penetration, low price, good vibration resistance, and relatively good weather resistance, so they are used in places with fog penetration and heavy dust, but due to their low light efficiency , the color rendering is not good, so it is already a light source of limited use. LED lights are rich in colors, long in life, and adjustable. At present, with the development of the LED industry, LEDs are gradually being promoted and used in road lighting. Only by understanding the characteristics of the light source can we choose the appropriate light source to meet the different needs of lighting. 5. Light pole design
The choice of lamps not only considers the photometric design, but also pays attention to the coordination with the light pole, especially whether the overall shape of the lamp and light pole meets the requirements of the road landscape. The environment where street lamps are used is on urban roads, not in open areas. The style of lamps and lamp poles directly affects the image of the city. Furnishings are coordinated. In the design of street lamps, we can't simply design one lamp for each road. We should consider the unified planning with the color of urban furniture within the scope allowed by the profession, and become a series of urban furniture. Of course, it is impossible to completely unify the requirements, and make unconventional designs for some roads with special characteristics, but also because of the development of unique special lamps. According to the above steps, determine the road lighting parameters, the selection of lamp light sources, the way of lighting arrangement, the design of lamp poles, and use these data for lighting calculation and subsequent construction drawing production.
Here are a few key points about the design:
1. The importance of lighting distribution
First of all, the main function of road lighting fixtures is to meet the functional lighting of the road. The light distribution of road street lights is different from other lighting fixtures, so non-road lighting fixtures must not be used for simple combination on the road. Otherwise, the illumination of the space will be generally too high, while the brightness of the road surface will be very low, or the excessively bright lamp head will cause severe glare. Here we can look at the particularity of road light distribution. From the linearity of the red line in the left picture, we can clearly see the bat-wing light distribution curve, so how to evaluate the quality of street lights through the light distribution of street lights. Take the street lamp light distribution shown in the figure as an example. The left figure is the curve of the C0-C180 plane. The 0 degree in the bottom middle of the figure refers to the directly below the street lamp, and the negative degree to the left is the reference line (0 degree ), the angle on the right side is positive. The center of the bat line is the light source point, and the red line is the line of equal light intensity. From the figure, the illuminance of each point on the C0-C180 plane can be calculated. For example, at 0 degrees, the light intensity is 2800cd, and the height of the lamp from the ground is 10M, then The illuminance is 2800/102=28LX, other angles can be calculated by adding trigonometric functions. It can be seen from the figure that the light intensity in the center is not the largest, but the light intensity on both sides is the largest. This is because the angle of the light to the road on both sides is different, and the distance between the light source and the ground is different, which makes the road lighting uniformity higher. This is Reasons for the importance of light distribution on road lighting design. 2. Light installation height (light pole height), spacing, cantilever length and elevation angle
The installation height of the lamps and the height of the lamp pole are mainly related to the effective width of the road surface, the way of lighting arrangement, the light distribution of the lamps and the power of the light source. At the same time, we should also consider factors such as maintenance conditions and economic aspects. Generally speaking, the lower the installation height, the lower the total investment. However, the reduction in installation height will lead to an increase in glare. Therefore, it is necessary to grasp the scale and proportion in the choice of height. The installation spacing of lamps is related to the way of lighting on the road surface, the light distribution of lamps, the height of lamp poles, and the longitudinal uniformity. The taller the light pole, the larger the spacing can be. But here we have to take into account the changes in the brightness of the road surface, because reducing the spacing can improve the longitudinal uniformity and improve the driver's comfort. The cantilever length of the lamp depends on the effective width of the road surface and the installation height of the lamp. The length of the cantilever should consider the lighting of the curb and sidewalk. Excessive cantilever length will reduce the visibility of the road surface. It is generally recommended that the cantilever length should not exceed 1/4 of the installation height. The proper elevation angle of the lamp installation can increase the illumination range of the road surface laterally, but if the elevation angle is too large, it will cause glare. 2. Problems encountered in urban road lighting design
1. Tree occlusion problem
Contradictions between the arrangement of street lamps and street trees often occur. The installation height, cantilever length, and position of lamps are directly related to the height of the tree, the denseness of the leaves, and the location of the tree hole. For low street trees with lush branches and leaves, if the installation height of the lamps is too high, the trees will seriously block the light, so that the light cannot reach the sidewalk and motorway, leaving a large area of shadow on the road. Of course, it is extremely beneficial to improve the efficiency of road lighting through the cooperation of the green management department to implement pruning, but we can't just hope for the cooperation with the green management department. The following points are the solutions in practice: By adjusting the distance between the light poles and using the light distribution of the lamps, the road is supplemented with light. Generally, there are many road reconstructions in this situation. If the tree hole position does not change, avoid the existing tree hole location directly, adjust the distance between lamps and adopt appropriate light distribution, and solve the situation that trees block the light to the greatest extent. By adjusting the length of the cantilever of the street lamp and avoiding the canopy of trees, the efficiency of lighting is greatly improved and the influence of leaves is greatly reduced. Lower the installation height of the lamps. The luxuriant part of the trees lies in the canopy. By lowering the installation height of the lamps and avoiding the shaded leaves, the maximum luminous flux can reach the ground. Of course, there are some disadvantages in doing so. The spacing between the poles will inevitably increase the total cost of road lighting. In desperation, the power of the light source was increased to compensate for the decrease in horizontal illuminance due to shading by leaves, but this resulted in an increase in glare and damage to the uniformity of brightness. 2. Lighting energy saving issues
Design Phase
Reasonable selection of lighting standard values: preventing two tendencies is mainly to prevent and overcome the idea that the brighter the better. Here is an explanation of why the brighter the better: the probability that the driver can effectively identify the target has a certain relationship with the average brightness of the road surface. The chance of detection increases significantly with the brightness of the road surface. However, when the brightness of the road surface exceeds 2cd/㎡, the increase in the detection probability of the driver to effectively identify the target is very small, that is to say, increasing the brightness of the road surface at this time does not help much to improve the visual visibility. It can be seen that excessive illuminance does not help to improve the road lighting effect, and is a manifestation of energy waste. Choose Efficient Lighting Fixtures
According to the standard, the 400W and 250W high-pressure sodium lamps can be used when the initial luminous efficacy reaches 110lm/w and 100lm/w respectively. However, if conditions permit, high-quality products should be selected, and the luminous efficacy can reach 135lm/w, which can save energy by 20% in terms of light source. According to the standard, conventional road lighting lamps can be used when the efficiency reaches 70%. If lamps with higher efficiency can be used, it can also bring about significant energy-saving effects, but remember not to fall into the misunderstanding of blindly pursuing high-efficiency lamps. Like the selection of energy-saving inductive rectifiers and electronic rectifiers, energy can also be saved. Optimize Lighting Design
Road lighting has various evaluation indicators, all of which must be met but not exceeded. The exact photometric data of the lamp must be known during design. After the lighting design is completed, the power density must be calculated to check whether it meets the LPD limit standard and optimize the lighting design. Comply with two standards (lighting standard and energy saving standard). Other stages
Reduce road brightness and illuminance level in the middle of the night: The first method is to turn off some lamps in the middle of the night to reduce the brightness and illuminance of the road surface. The second method is to turn off one light source in the same lamp late at night. The advantage is that it is simple and convenient, the uniformity is unchanged, and the energy saving effect is obvious. The disadvantage is that the investment increases.
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