Plastic film serves as an insulator, with the turbidity of greenhouses increasing with rising external temperatures and decreasing with lower temperatures. Seasonal changes are pronounced, with significant differences in day and night temperatures. The greater the temperature drop, the wider the temperature range. Generally, in the cold season, the daily temperature rise in greenhouses can reach 3-6 degrees, but only 1-2 degrees on cloudy days or at night. In spring, the temperature difference between greenhouse surfaces and open ground gradually widens, with temperatures rising from 6-15 degrees. As external temperatures rise, greenhouse temperatures also increase relatively, potentially reaching over 20 degrees. Thus, greenhouses face risks of both high temperatures and freezing, necessitating manual regulation. During the hot season, greenhouse temperatures may exceed 50 degrees, requiring full ventilation. Greenhouses are covered with straw curtains or "shade cloths," which can lower the temperature by 1-2 degrees compared to the outside. At night in winter, the low temperatures in greenhouses are 1-3 degrees higher than those in open areas, and on cloudy days, they are similar. Therefore, the main production season for greenhouses is spring, summer, and autumn. By using insulation and ventilation, greenhouse temperatures can be maintained between 15-30 degrees.

New plastic film can achieve a light transmittance of 80-90%, but due to factors such as dust pollution, water droplet adhesion, and film aging, the transmittance can drop by 10-30%. The lighting conditions in greenhouses vary greatly with the season, weather conditions, and types of vegetation (canopy structure, orientation, scale, etc.). The larger the greenhouse, the greater the vertical radiation intensity differences inside, with a difference of 20-30% between the upper and lower levels. In winter, the lighting conditions from east to west in greenhouses are better than those from north to south, and the local lighting conditions are also similar. However, the radiation intensity difference between the north and south sides of a greenhouse extending from east to west can reach 10-20%. Different greenhouse structures greatly affect light reception, although double-layer film provides better insulation, it reduces light reception by about half compared to single-layer film. Additionally, the use of multi-span greenhouses and different greenhouse materials has a significant impact on light reception. Greenhouses with a single-layer steel and plastic structure receive better light, with a light transmittance only 28% lower than that of open ground.

Greenhouse lighting conditions are poor. Therefore, when constructing greenhouses, it's advisable to use lightweight materials that can withstand certain loads, simplifying the structure without compromising light transmission. This ensures the greenhouse remains sturdy, economical, and practical. The light transmission capabilities of different greenhouse structures vary, with the greenhouse's lux (thousand) light transmission rate, and the transmission rate (percentage) differing for single-layer steel structures, single-layer bamboo and wood structures, single-layer rigid plastic structures, and multi-span reinforced concrete ground control membranes. During the covering period, dust pollution can significantly reduce the transmission rate. After two days of using new membranes, dust pollution can decrease the transmission rate by 14.5%. After 10 days, it drops to 25%, and in a month, it's less than 28%. Generally, dust pollution can reduce the transmission rate by 10-20%. In severe cases, the light in the greenhouse can be only 7%, making it unusable. Generally, thin films easily absorb moisture, causing condensation into water droplets on the film, which can lower the transmission rate by 10-30%. Therefore, preventing film pollution and water droplet condensation is a crucial measure. Additionally, during the use of films, due to high and low temperatures, sunlight, and ultraviolet radiation, films can "age." After aging, the transmission rate of the film can drop by 20-40%, even losing its usability. Therefore, the film covering the greenhouse should be a long-lasting film that withstands temperature, aging, dust, and leak prevention to enhance the greenhouse's lighting, increase temperature, and prolong its service life.

That's it for the requirements of greenhouse film in terms of temperature and light exposure. Only then can the film effectively fulfill its purpose; otherwise, it's all waste.