Abstract: In order to figure out the influences of thermal insulation quilt on the light environment in different positions in the greenhouse, the light distributions in different positions (from east to west) in the greenhouse were analyzed. The simulation and actual measurement were conducted in the Spring and Autumn Equinox Day in this study. Shading from direct sunlight in greenhouse was studied through converting the three-dimensional solar altitude angle into two-dimensional angle. Moreover, the movement position and distance of the shading zone from east to west were calculated in the Spring and Autumn Equinox Day. The distribution of daily light integral (DLI) was simulated in the greenhouse in different positions. The simulated greenhouse span was 12m, the ridge height was 4.2m, and the length was 60m The steel arch above the ground was 16m long, the radius was 0.35m, and the diameter was 0.7m after the insulation was rolled up. Ethylene vinyl acetate (EVA) film with actual light transmittance at 65% was used in the greenhouse. The light intensity of different positions in the top roll of insulation quilt in greenhouse was measured and the DLI was calculated. The measured value was compared with the simulated value. The distribution of DLI at different positions in the east-west direction and the light distribution in the greenhouse were analyzed. The results based on the model showed that the DLI at the middle point in east-west direction of greenhouse was the smallest, which was 10.91mol·m−2·d−1. The DLI was lower within 1m from the middle point to east/west, which increased by 11.8% from 10.91mol·m−2·d−1 to 12.20mol·m−2·d−1. DLI increased with the increased distance from the middle to the east/west, and the maximum value was 13.70mol·m−2·d−1, which was 6m away from the middle point (the edge of the greenhouse). The measured results showed that the DLI in the greenhouse was also the smallest at the middle point of the east-west direction, which was 7.31mol·m−2·d−1. The DLI was also lower within 1m from the middle point to east/west, which increased by 3.4% from 7.31mol·m−2·d−1 to 7.56mol·m−2·d−1. Similar trends were observed in the measured results, and the maximum value was 12.70mol·m−2·d−1. The variation law of DLI in measured values was consistent with the simulated values, which were the smallest in the middle point of greenhouse, and DLI increased with the increased distance from the middle to the east/west. The DLI changed slightly in different positions from east to west in the greenhouse. However, this does not affect the accuracy of the simulation trend. The simulation values were consistent with the measured values. In conclusion, DLI in the middle region will restrict the growth of photophilic crops in the season with poor light environment, thus leading to light stress on the growth of vegetables and other light-loving crops in the greenhouse.

Key words: Top roll of insulation quilt, Plastic greenhouses, Shading shadows, Daily light integral, Light distribution model