Test method and principle of illuminance meter
1. The principle of illuminance test
Illuminance is the areal density of the luminous flux received on the illuminated plane. Illuminance juice is an instrument used to measure the illuminance on the illuminated surface, and it is one of the most widely used instruments in illuminance measurement.
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2. Structural principle of illuminance meter
The illuminance meter is composed of two parts: a photometric head (also known as a light receiving probe, including a receiver, a V (λ) pair filter, and a cosine corrector) and a reading display.
Measurement steps and methods
In a work room, the illuminance should be measured at each work location (eg desk, workbench) and then averaged. For an empty room or non-working room without a confirmed working location, if only general lighting is used, the illuminance is usually measured on a horizontal plane with a height of 0.8m. Divide the measurement area into grids (or close to squares) of equal size, measure the illuminance Ei at the center of each grid, and its average illuminance is equal to the average of the illuminance at each point, that is
Where Eav - the average illuminance of the measurement area, lx;
Ei ——the illuminance at the center of each measurement grid, lx;
N - the number of measuring points.
Uniformity of illuminance refers to the ratio of minimum illuminance to average illuminance on a specified surface, namely:
In the formula, Emin——refers to the minimum illuminance on the measured surface, lx.
In this experiment, the surface of the measuring point arranged in the room can be used as the designated surface, and the minimum illuminance can be regarded as the minimum illuminance value in the measured point.
Measure the side length of each square in the room as lm, and a large room can be
Where Eav - the average illuminance of the measurement area, lx;
Ei ——the illuminance at the center of each measurement grid, lx;
N - the number of measuring points.
Uniformity of illuminance refers to the ratio of minimum illuminance to average illuminance on a specified surface, namely:
In the formula, Emin——refers to the minimum illuminance on the surface to be measured, lx.
In this experiment, the surface of the measuring point arranged in the room can be used as the designated surface, and the minimum illuminance can be regarded as the minimum illuminance value in the measured point.
Measure the side length of each square in the room as lm, and a large room can take 2-4 m. In narrow and long traffic sections such as walkways and stairs, the measuring points are arranged along the center line of the length direction, with a spacing of 1-2 m; the measuring plane is the ground level or a horizontal plane 150mm above the ground.
The more the number of measuring points, the better the average illuminance value obtained, but it also takes more time and energy. If the allowable measurement error of Eav is ±10%, the workload can be reduced by selecting the least measuring points according to the room shape index. The relationship between the two is listed in Table 1. If the number of lamps is exactly equal to the number of measuring points given in the table, the measuring points must be added.
