Under what conditions does the illumination level of the blackboard lamp meet the high requirements?
Compared with classroom lamps, we need to pay more attention to the lighting of the blackboard. The difficulty of blackboard lamps is higher than that of classroom lamps. Generally, two single-tube fluorescent lamps are used as lighting lamps for classroom blackboards, and the installation position and height of blackboard lamps are They are relatively fixed, and the distance between the upper and lower sides of the blackboard is very large. How to make the illumination level of the blackboard meet the high requirements under such conditions is a big problem. Here we use a specific example to illustrate:
The specific size drawing of the blackboard lamp installed in a classroom, through calculation, we can get that the angle between the two straight lines from the center of the lamp to the top and bottom edges of the blackboard is about 35°. If most of the light output of the blackboard lamps can be concentrated within a 40°-45° angle, we can make the most of the lamps. It is a light distribution curve diagram of a blackboard lamp that can reasonably distribute the light output, from which we can see that most of the luminous flux in the direction of 270°-0° of the lamp is concentrated in the range of 300° to 345° (we use 50% of the maximum light intensity between the two rays), and the light output near 300° is less than that near 340°. According to the relevant size calculation, the distance from the blackboard lamp to the lower edge of the blackboard is basically 1.75 times the distance to the edge of the blackboard, so the light output to the lower edge of the blackboard should be more, so that the illumination on the blackboard will be more uniform. .
If the design of the blackboard lamps is not reasonable enough, there will be several situations after installation:
1. The light output is too concentrated, causing the central part of the blackboard to be too bright and the peripheral part too dark, and the uniformity of illumination will be unqualified. As shown in Figure 5, the light output of the luminaire in the direction of 270°-0° is also very concentrated, but it is too concentrated. The light output of the lamp is basically in the range of 30°, and it is difficult to take care of the upper and lower edges of the entire blackboard, and there will inevitably be a situation where the uniformity of the blackboard is too low at one end.
2. The light distribution of the lamps is too scattered, and the central light intensity is not prominent, so the situation that the edge of the blackboard is too bright and the lower edge is too dark does not meet the requirements. As shown in Figure 6, the light intensity changes at 270°-0° and 0°-90° of the lamp are not obvious, and the light intensity directed to the upper edge of the blackboard and the lower edge of the blackboard are basically the same. The distance we estimated before installation is 1.75 times. The relationship between distance and light intensity can be calculated to show that the difference in illuminance is about 3 times. In this way, the illumination uniformity finally obtained is about 0.5 and it is difficult to meet the requirement of 0.7.
3. The light distribution shape of the lamps meets the requirements, but the total luminous flux of the light source is too low, so that the average illuminance of the entire blackboard cannot even meet the minimum standard of 500lx.
in conclusion
1. There are many types of classroom lamps, and there is no absolute distinction between good and bad. The key is to combine the lamps with the final use place. Only by using the lamps reasonably can the biggest characteristics of the lamps be used, and the advantages can be avoided, so as to improve the illuminance and reduce the energy consumption. .
2. The light intensity distribution of the lamps should be considered in the design stage of the blackboard lamps, and the light should be reflected to the place where it is needed. The lamp efficiency of the blackboard lamp can not really reflect the actual use effect of the lamp, and it depends on whether the 50% maximum light intensity angle is reasonable.
