Misunderstanding Analysis of Light Distribution Design of LED Road Lighting

1 Introduction

LED lighting is experiencing a rapid development period. Under the leadership of the government, China's LED road lighting is in the demonstration stage. Due to the unevenness of the manufacturers and their employees in the industry, it is inevitable that there are many conceptual misunderstandings. Combined with many commercial propagandas that are not true or false, some misunderstandings will inevitably have a directional misleading effect on the development of the entire lighting industry. For example, the popular rectangular light distribution principle in the industry has been accepted by many manufacturers or “experts” and promoted by “writing in national or local regulations” in an attempt to promote its lighting products. This has already been applied to the LED road lighting industry. Healthy development has had an adverse effect.

2. Rectangular light distribution principle in LED road lighting industry

At present, the principle of rectangular light distribution prevailing in the road lighting industry in China only considers the uniformity of illumination and the utilization of light, and considers the design of the light emitted from the luminaire according to the light intensity at a certain angle and different angles. method. As shown in Figure 1, four directions in the C-γ coordinate system (C=25° γ=62°), (C=155° γ=62°), (C=185° γ=60°) and (C=355° γ=60°) a quadrangular pyramid, in which the light intensity values ​​in all directions are solved according to the method of equations (1) to (3) in the solid angle range, and the formula is obtained. 4).

Where 0—the ground illumination below the luminaire, ie C=0°γ=0°; E 0—the light intensity directly below the luminaire, ie C=0°γ=0°; I h — installation of the luminaire Height, the vertical distance from the optical center of the luminaire to the ground; (C, γ) - the ground level illuminance value produced by the luminaire in the C-γ direction; E (C, γ) - the intensity value of the luminaire in the C-γ direction; IE—The illuminance uniformity factor to be designed for single luminaire illumination. U From equations (1) to (3), it is convenient to derive the calculation formula of the light intensity value of the luminaire in all directions of C-γ, as shown in formula (4):

3. Luminance analysis and calculation of rectangular light distribution principle

3.1 Calculation method of light intensity and brightness

In this section, according to the formulas (1) to (4), it is assumed that the illuminance directly below the pole is 40 0 ​​E   0.5 1800 lx, and the height of the pole is m, from which it is calculated that the illuminance uniformity coefficient at that time is assumed, and the other parties are upwards. The illuminance uniformity coefficient is calculated by linear interpolation (as shown in Table 1). For the convenience of analysis, when calculating the brightness, first consider the light intensity distribution of each γ angle in the C0-C180 plane, and assume that the driver's line of sight is in the C0-180 plane, and the light exit plane and the road surface are parallel, that is, no elevation angle is installed. After simplifying the process, when C=0°, when C=180°, β, its light intensity calculation and brightness calculation result are shown in Table 1. The calculation of the brightness in the table uses the calculation method [1] in the CIE140-2000 specification, as shown in equation (5).

Where p—the brightness value of the calculated point p on the road surface;

L r(β, ε)—calculates the simplified luminance coefficient at point p [2], and finds the R3 table in CIE 144-2001;

β — observe the angle between the line of sight and the plane of the incident ray [1];

Ε—incident angle [1] at which incident light illuminates to the point P.

2. The maximum value of γ in the table is 62.5°, which is different from the one shown in Figure 1, but does not affect the calculation and analysis in this paper. To determine the maximum gamma angle on each C plane, it should be calculated separately based on the geometric relationship.

3. The value of (βε, ) in the table is found according to the simplified brightness coefficient table of R3 asphalt pavement in CIE144-2001 standard, or calculated by linear interpolation method [1~2]. r

4. Since the beam control of the rectangular light distribution in the text is strict, only one fixture in the brightness calculation area provides brightness, so the single-lamp brightness calculation method is adopted, and the road surface brightness in CIE140-2000 needs to calculate the brightness of 5~6 lamps ( Determine the number of lamps when calculating the brightness according to the height ratio) [1].

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