Luminosity refers to the degree to which an object is illuminated. It is expressed by the luminous flux received per unit area, and the unit is lux [x] (Lux, lx), which is 1m/m2. 1 lux [ The luminous flux equal to 1 lumens [ming] (lumen, lm) is the illuminance evenly distributed on an area of 1m2. The illuminance is based on the luminous flux received by the vertical plane as the standard, and the illuminance will decrease if it is irradiated obliquely.
Calculation of illuminance
The calculation methods of illuminance include the coefficient method, the approximate curve method, the specific power method and the point-by-point calculation method.
(1) Utilization coefficient method
1. The concept of utilization coefficient
The utilization coefficient of the illumination light source (utilization coefficient) is the luminous flux projected on the working surface (Including the direct luminous flux and the luminous flux reflected on the working surface from multiple directions) and the ratio of the luminous flux emitted by all light sources to express,
that is, u=φe/nφ
Utilization factor u It is related to the following factors:
1). It is related to the type, light effect and light distribution curve of the lamp.
2). It is related to the hanging height of lamps and lanterns. The higher the suspension, the more reflected light flux and the higher the utilization factor.
3). It is related to the area and shape of the room. The larger the area of the room and the closer it is to a square, the more direct luminous flux will be, and the higher the utilization factor will be.
4). It is related to the color and cleanliness of walls, ceilings and floors. The lighter the color, the cleaner the surface, and the more reflected light, so the utilization factor is higher.
2. Determination of utilization coefficient
The utilization coefficient value should be determined according to the reflection coefficient of the wall and ceiling and the illuminated space characteristics of the room. Illuminated space characteristics of the room
Use a "roomcabinrate" (roomcabinrate, abbreviated as RCR) parameter to characterize.
A room can be divided into three spaces according to different illumination conditions: the top is the ceiling space, the floor space below the working surface, and the middle part is called the room space. There is no ceiling space for rooms with ceiling lamps or recessed luminaires; and for rooms with a ground surface, there is no floor space.
Room space ratio RCR=5hRC(l+b)/lb:
In the formula, hRC--room space height;
l---room Length;
b--The width of the room.
According to the reflection coefficient of the wall and ceiling (see Table 8-1) and the room space ratio RCR, the utilization coefficient can be found from the corresponding lamp utilization coefficient table.
3. Calculate the average illuminance on the working surface according to the utilization coefficient method
Due to the luminous efficiency of the light source itself during the use of the lamp, the light The walls and ceiling of the lighting site may also be stained, which reduces the luminous flux on the working surface. Therefore, when calculating the actual average illuminance on the working surface, a "dimming coefficient" of less than 1 should be included. Therefore, the actual average illuminance on the working surface is
Eav=uKnφ/A
where u____ utilization coefficient;
K____ dimming coefficient (also known as Maintenance factor), the reference value is listed in Table 8-3;
n____the number of lamps;
φ____ the luminous flux emitted by each lamp;
A____ Illuminated room area
The basic unit of the illuminance test value is LUX, and the commonly used test software is DIALux. Lighting designers often use this software to simulate the illuminance value of a certain area indoors and outdoors. The test value is the theoretical value under the optimal condition of the light source. Due to the reflector and light source of the lamp, there is a certain difference between the theoretical value and the actual test value.