According to the covering materials, there are plastic film greenhouse, sunlight plate greenhouse and glass greenhouse. For greenhouse, it is necessary to control light, temperature, humidity and CO2 concentration. Here we mainly discuss the light control of covering materials.
Although the spectrum of sunlight reaching the earth's surface is very wide (280 nm to 2 μ m), for most green plants, only 400-520 nm (blue) light and 610-720 nm (red) light contribute most to photosynthesis. Therefore, the visible light band has the greatest impact on plants.
At the same time, the scattered light can penetrate the bottom of the plant, and the light illumination is more gentle and uniform, so as to avoid local sunburn of the top leaves, as shown in Fig. 1. Compared with direct light (direct light: single direction of propagation), scattered light (scattered light: spread around, no definite direction) is more conducive to photosynthesis of plants, thus increasing plant yield (reference 1).
Researchers from Wageningen University in the Netherlands and Greek researchers have confirmed that when using a diffusive polyethylene film, plant yield is significantly increased in summer, and better results are obtained in winter when transparent film is used (ref. 2).
Therefore, if there is an intelligent dimming film, which can automatically switch the specific gravity of scattered light and direct light in winter and summer, it can perfectly solve the different requirements of sunlight in Greenhouse in winter and summer.
The intelligence of the intelligent adaptive dimming film is that in summer, when the temperature of the dimming film reaches a certain preset temperature due to sunlight irradiation, the dimming film will automatically change from transparent state to foggy white state (the regulation range of the specific gravity of scattered light is up to 55.8%), which will convert direct sunlight into scattered light; in winter, due to the low temperature, the dimming film will be transparent, so that Sunlight can enter the greenhouse directly without interfering with sunlight. In winter, it is mainly direct light, keeping transparent; in summer, it is mainly scattered light, keeping fog white. This characteristic is in line with the results mentioned above.