I. Purpose of measurement After the road lighting proje […]
I. Purpose of measurement
After the road lighting project is completed and put into operation, it is usually necessary to measure the brightness and illumination of the road surface. The purpose is to understand whether the actual lighting effect of the road surface meets the original design requirements, and to provide a basis for more economical and reasonable design in the future. Sometimes, after a period of time (such as half a year, one year) of operation of lighting facilities, measurements are also needed. The purpose is to study the light output reduction caused by dirty ash accumulation of lamps and lanterns, and to find out the maintenance factor.
2. Measurement of road illumination
Generally speaking, the illumination of a point on the road contains two meanings: (1) the average illumination of a small area containing the point (determined by the size of the receiver). (2) The general illumination refers to the illumination of the point on the horizontal plane, i.e. the horizontal illumination, in addition to the special indication.
The average illumination of a road surface is usually expressed in terms of formulas.
Eav = fE / F dA
That is to say, the measured road surface is divided into many small grids, and the illumination distribution on each small grids is considered to be uniform. Then the illumination on each small mesh is measured. Finally, the illumination value on each small mesh is multiplied by the area of the corresponding small mesh, and then divided by the sum of these small mesh areas, the average illumination of the measured road surface is obtained.
Thus, when measuring the average illumination of a certain section of road surface, the first step is to divide the section of road surface into many small grids (usually square or rectangle with equal area), and then measure the illumination of each grid, the rest is the calculation problem.
2. Selection of Measuring Section
When measuring illumination, the road section that can represent the illumination condition of the road under test should be selected. For example, if there is a road with a minimum installation distance of 35 m, a maximum of 40 m and a majority of 37 m, the section with a distance of 37 m should be selected as the measuring field.
In addition, the consistency of light sources and the regularity of fixture installation (including cantilever length, elevation, installation height, etc.) should also be considered. In the longitudinal direction (along the road), the measuring field should include the area between two lamp poles on the same side, while in the horizontal direction, the whole width of the road should be considered for the lamp layout on one side, and the width of the road should be 1/2 for the lamp layout on both sides staggered and symmetrical or centrosymmetrical. When environmental lighting conditions need to be investigated, the lateral measurement area should extend the lane width from the edge of the road to the outside.
3. Point distribution method for illumination measurement
The central method. The measuring section between two lamp poles on the same side is divided into several rectangular grids of equal size, and the measuring points are set at the center of each rectangular grid. This method is based on the assumption that the illumination measured at the center of the grid represents the illumination of the whole grid. For example, the layout of measuring points for two-lane roads shown in Figure 9-3 when central fabrication is used.
The problem now is how many grids to divide the measuring section? GB/T 15240 of Outdoor Lighting Measurement Method of China stipulates that when the uniformity of road illumination is poor or the accuracy of measurement is high, the number of grids to divide should be more, that is, the points should be arranged more closely. When the distance between two lamp poles is 5::: _50m, the distance (5) is usually divided into ten equal parts along the longitudinal direction of the road. When 5 > 50m, equal spacing is divided according to the principle of D5M edge length of each grid. In the horizontal direction of the road, each lane is divided into two parts (four-point method) or three parts (center method). When the uniformity of road illumination is good or the accuracy of measurement is low, the width of lane can be taken as the width of grid in the cross direction of road, that is, no further division is needed. By using these two methods, the number of measuring points is not much different, but the calculation of average illumination from measuring results will be slightly different. We'll see that soon. No matter which method is adopted, it is not necessary to draw the grid completely in advance and then distribute the points. The measuring points can be directly marked on the road surface by measuring and calculating in advance.