LED street light distribution research

LED street light distribution research

0 Preface

LED (Light Emitting Diode) is a new solid-state light source that is competitive in the 21st century. Compared with traditional light sources, it has the advantages of small size, long life, low energy consumption and flexible control. In road lighting, with the development of white LED technology, the luminous flux of single-chip LEDs continues to increase, and the replacement of traditional light sources for LED streetlights will become a trend. The light intensity distribution of the light source in all directions of the space is the light distribution. LED street light distribution is to make the light as much as possible to the various areas of the road surface to obtain the light distribution that meets the requirements of road lighting. Whether the LED street light distribution design is accurate or not is one of the key factors that can replace the traditional street lamp. Studying the LED street light distribution is of great significance to the future system design research of LED road lighting.

1 LED street light distribution features and requirements

1. 1 LED street light distribution shape characteristics

In road lighting, if there is no light distribution to the LED street light source, the light pattern on the road surface is a circular spot with a large area, and some of the light is scattered outside the road surface and is not used, as shown in Figure 1(a). Shown. In order to meet the requirements of brightness, illuminance and uniformity of the road surface, and to distribute most of the light on the road surface as much as possible to improve the utilization of the light and reduce unnecessary waste, it is usually necessary to illuminate the LED street light. The light pattern or spot formed by the light output from the street light on the road surface is preferably a rectangle, as shown in Fig. 1(b).

Figure 1 LED street light distribution diagram

1.2 Road lighting standard light distribution requirements

According to the requirements of "Urban Road Lighting Design Standards", the roads in road lighting are divided into express roads, trunk roads, secondary trunk roads and branch roads. The standard values ​​of LED road lighting light distribution requirements should meet the requirements of Table 1.

Table 1 Road lighting standard values

The current research on LED street lamps is mainly focused on the application of secondary trunk roads and branch roads. The small luminous flux is the main reason why LED street lamps cannot be applied to the main road. The application on the trunk road has yet to be researched and developed by LED technology.

1. 3 LED street light distribution curve

The spatial distribution of luminous intensity is often referred to as the "light distribution curve." Below the street light, the light intensity should be minimal, and as the elevation angle θ increases, the light intensity Io increases. The function relationship is , that is, the distribution curve expression. The ideal and light distribution curve of a single luminaire for road lighting is shown in Figure 2. Due to the complexity of the optical design, the light distribution shape is difficult to fully conform to the functional relationship, and the projection range of the θ angle can be reduced, and the spacing of the lamps can be reduced to obtain uniform illumination. In general, it is desirable to achieve a wide-angle "batwing" shape after light distribution.

Figure 2 ideal light distribution curve

2 LED street light distribution scheme and analysis

The light distribution scheme of LED street lamps is based on the requirements of road lighting, and it is necessary to consider controlling glare and considering environmental factors. For road lighting, the light effect and the light distribution curve are two important parameters. At present, the LED street light distribution scheme mainly has the following basic forms.

2.1 LED light distribution once

In the power LED manufacturing process, the lens process can improve the light efficiency, reduce the light output loss, and change the light output characteristics. The LED package lens process has a certain relationship with the high-power LED street light illumination. With a well-packaged lens design, LEDs can achieve better light output characteristics.

The LED light distribution in the double-head lens package can transform the light intensity output curve of the single LED into a "batwing" shape, so as to further realize the "batwing" shape light distribution of the entire light intensity output curve of the entire street lamp. The double-lens primary light distribution structure and light distribution curve are shown in Fig. 3(a) and Fig. 3(b), and the lens is designed as a primary light distribution core.

Fig. 3 Schematic diagram of LED light distribution structure and light distribution curve of double lens package