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Free Illumination Design of Arbitrary Illumination Distribution in LED Road Lighting
- May 15, 2017 -

At present, there are a number of studies to achieve a single LED light source on the road to form a uniform illumination of the rectangular spot as the goal, the LED secondary optical design,


This optical design can indeed be achieved through the splicing of the entire road illumination uniform, but in practical applications, but there will be many problems. As shown, the two street lighting area of the splicing will appear only the road to receive the light of the situation, if the individual is located, the driver on the road may not be able to observe his presence, easily lead to traffic accidents. Although the above problems can be solved by overlapping stitching, the brightness uniformity of the road surface is poor and can not meet the driving requirements. Therefore, in the road lighting in the street light in the longitudinal direction of the illumination distribution should be non-uniform, the overall presentation of the middle strong, weak distribution at both ends, and through the appropriate overlap stitching to achieve the longitudinal distribution of illumination uniform.


Which is defined as the ratio of the average level illuminance in the strip area of 5 m wide outside the roadway to the average horizontal illuminance on the adjacent 5 m roadway. For example, it is usually required that SR> 0.5. If the street light on the road to form a uniform illumination of the rectangular spot, in order to meet the requirements of the environment than the width of the lighting area will be wide, reducing the light efficiency. Considering the environmental ratio and the efficiency factor, the illumination distribution in the direction of the road width should also be changed, and the illuminance on both sides of the roadway is decreasing.


Based on the above considerations, road lighting in a single street lamp in the road length and width of the illumination distribution should be a specific distribution. In order to realize this distribution, this paper presents a new type of LED free optical surface design method to realize arbitrary illumination distribution. The separation variable is combined with the minimum energy block iteration method. This method through the LED light source and the road energy grid division, between the two formed a mapping. For this mapping, the lens surface is constructed according to the edge ray theory, the Snell law and the error control method. The design process takes into account the installation of the location and angle of the street lights, and finally to achieve a single street lamp in the road surface and vertical illumination were a specific distribution of the LED optical system.


1 Lens design method Assuming that the center S of the LED light source is at the origin of the orthogonal coordinate system, the incident light is refracted by the free surface of the refractive index as the outgoing ray M, and the refractive index of the outer space of the lens is /. The plane corresponds to the point (:, 3,), and illuminates the point.


According to the Snell's law, at the point P on the free surface, the incident ray 3, the outgoing light 0 and the normal vector N satisfy, where 7, and are the unit vectors. Combining the energy correspondence and the edge ray theory, we can get the coordinates of the point P (, y, z) on the free surface and the normal vector 10. The design process of the free-form surface lens is divided into two steps, namely, the energy mapping relation And the construction of the lens surface. When the energy mapping relationship is established, assuming that the energy emitted by the light source is equal to the light energy of the illuminated receiving surface, the energy conservation integral equation can be expressed as the light intensity of the light source corresponding to the light exit direction i, indicating the light exit angle (EG) denotes the illuminance of point P on the receiving surface, and D denotes the illuminated area on the receiving surface M. The method of establishing the energy mapping relationship proposed in this paper is the combination of the separation variable and the minimum energy block iteration. The traditional separation variable method can be used in uniform illumination LED street lamp lens design, can get better results. However, for the road illumination distribution in the road transverse and vertical are not uniform street lamp lens design, the simple use of the results of the separation variable method is not ideal, which is the limitations of the lens design software has a relationship. This paper can solve this problem effectively by combining the minimum energy block iteration method。



The LED light source is divided by the separation variable method. As shown in (a), the energy of the light source is divided into a number of energy bars in the direction of 0, and the luminous flux of each energy bar can be obtained by the following equation (3): the energy of the length of the receiving surface is followed by the minimum energy block iteration Division. The receiving surface is divided into a plurality of elongated strips with a sufficiently small gap mm in the longitudinal direction. Since the illuminance distribution on the receiving surface is known, the luminous flux received by each elongate strip is known and the luminous flux is superimposed in turn, When the luminous flux reaches the luminous flux of the energy bar corresponding to the light source, the superimposition of the starting and ending strips is the boundary of the energy bar corresponding to the light source. After multiple iterations, the receiving surface can be divided into multiple energy bars in the length direction, corresponding to the energy bars of the light source. (B) shows the energy bars divided by the length of the receiving surface, and the width of each energy bar is related to the illuminance distribution of the road surface.


The LED light source is divided by the separation variable method. As shown in (a), the energy of the light source is divided into a number of energy bars in the direction of 0, and the luminous flux of each energy bar can be obtained by the following equation (3): the energy of the length of the receiving surface is followed by the minimum energy block iteration Division. The receiving surface is divided into a plurality of elongated strips with a sufficiently small gap mm in the longitudinal direction. Since the illuminance distribution on the receiving surface is known, the luminous flux received by each elongate strip is known and the luminous flux is superimposed in turn, When the luminous flux reaches the luminous flux of the energy bar corresponding to the light source, the superimposition of the starting and ending strips is the boundary of the energy bar corresponding to the light source. After multiple iterations, the receiving surface can be divided into multiple energy bars in the length direction, corresponding to the energy bars of the light source. (B) shows the energy bars divided by the length of the receiving surface, and the width of each energy bar is related to the illuminance distribution of the road surface.


This lens is placed into the road lighting system for simulation, to get a single street light on the road surface illumination as shown.

 

The simulation results are compared with the given road illumination distribution, and the illumination distribution in the road length direction is shown as 0, for different road lengths and in the road width direction. The total illumination uniformity on the roadway is 0.93 and the ambient ratio is 0.55, which meets the design requirements.

 

3 Conclusion In order to achieve the road lighting in the road total illumination and brightness uniformity, and at the same time to meet the environmental requirements, single street lights in the road length and width of the illumination should show a specific distribution. The free optical surface design method proposed in this paper can effectively realize the arbitrary illumination distribution of the road surface. Based on the law of conservation of energy, the separation of variables and the minimum energy block iterative method is used to mesh the light source and the receiving surface, and the energy mapping is formed between the two. For this mapping, the lens surface is constructed according to Snell's law, edge ray theory, and error control method. In addition, this paper analyzes the optimal placement angle of the street lights, LED and the center line of the road line perpendicular to the poles when the most conducive to the design and production of street lamps. In this paper, the street lamp lens is designed with the cosine distribution of the given road length and the trajectory of the width direction is taken as an example. At the same time, the position and angle of the street lamp are analyzed synthetically, and the asymmetric discontinuous free surface lens is obtained. The simulation results show that the illumination is close to the cosine distribution in the direction of the pavement, and the error is less than 6%. The illumination in the pavement width direction is close to the trapezoidal distribution with the error of less than 10%. The total illumination uniformity of the pavement reaches 0. 93, the environment ratio is 0.55 , To meet the requirements of road lighting. This method can effectively achieve the arbitrary illumination distribution of the LED optical system design, especially for road lighting street lamp lens design.


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