Why should light be controlled for Chinese orchids in the north?

Organic matter comes from photosynthesis. Photosynthesis is completed with water and carbon dioxide as raw materials, chloroplasts as the factory, and light energy as the driving force (releasing oxygen). Without the driving force, photosynthesis cannot proceed, which shows the importance of light. It is generally believed that the light intensity usable by Chinese orchids is 20%-30% of the maximum natural light intensity. The maximum natural light intensity in Jinan can reach about 100,000 lux, which means the light intensity usable by Chinese orchids cannot be higher than 15,000-20,000 lux. For this, the author selected potted orchids in early December to enter the greenhouse. Because the greenhouse is made of 5 mm glass, it lacks short-wave light. The temperature is high and plants easily grow leggy, so in early March the potted orchids were moved into a flower bed, and the flower bed was protected against cold with 0.4 mm plastic film, because this film can transmit 98% of ultraviolet light with a wavelength of 0.4-0.32 microns, and can transmit 90% of ultraviolet light with a wavelength of 0.32-0.28 microns; the heat transmittance is 84%. It is both close to natural light and insulated, and furthermore the film can be uncovered to directly receive weak light of about 10,000 lux, thereby increasing the utilization rate of light energy and promoting the growth and development of Chinese orchids. At the end of June and early July, Jinan enters the rainy season, the relative air humidity increases, and then the potted orchids are moved into a flower shed, with one or two layers of shade netting used as appropriate for shading. Shandong Academy of Agricultural Sciences Wang Tao