In the winter and spring seasons, light conditions inside plastic greenhouses play a crucial role in the growth, yield, and quality of vegetables. Proper lighting is essential for photosynthesis and overall plant development. So, how can we improve the light conditions within a greenhouse?
First, optimizing the structure of the greenhouse can significantly enhance light availability. The choice of building materials matters—using galvanized iron wire No. 8 to secure the frame not only saves on materials but also reduces shading, making it more efficient and practical. It's recommended to use non-drip films for the cover, as they prevent condensation from forming, while regular polyethylene films are suitable for general use. Additionally, using white construction materials and painting walls white can increase light reflection and extend the lifespan of the structure. Raising the height of the greenhouse can also improve light penetration.
The orientation and angle of the greenhouse should be adjusted based on its usage and the light requirements of the crops. For spring and autumn production, a shallower angle (around 15 degrees) is ideal, allowing even light distribution. In contrast, during winter, a steeper angle (about 25 degrees) helps maximize sunlight exposure by creating an arched roof.
The width of the greenhouse and the slope of the back wall also affect lighting. For winter production, a width of 6–6.5 meters with a rear slope of 0.8–1 meter is optimal for both light and insulation. In spring and autumn, a wider structure of 8–9 meters with a narrower rear slope (0.5–0.7 meters) or no slope at all can help balance light and temperature.
When planting different vegetable varieties, following the principle of "lower in the north, higher in the south" ensures that taller plants don't block the light from shorter ones. Proper cultivation practices, such as pruning and training, also help improve light access. For example, tilting the front row of cucumber plants toward the south, keeping the middle rows upright, and positioning the back rows to the north can increase light utilization by up to 10%.
Maintaining clean greenhouse film is vital. Water droplets and dust on the film can reduce light transmission by as much as 30%, so regular cleaning is necessary. After snowfall, removing snow promptly increases transparency and light levels. Covering the outside of the greenhouse with insulating materials like straw can also help, provided it doesn’t drastically lower the internal temperature. Early removal of covers in the morning ensures more light reaches the plants, and after releasing humidity for about 30 minutes post-sunrise, water droplets on the film can be reduced, further improving light transmittance.
Artificial lighting is essential during the dark winter months or in greenhouses with insufficient natural light. Light intensity should be around 1,000 to 3,000 lux. Using red and blue-violet lights, such as three 40W fluorescent lamps placed 45 cm above the seedlings, can provide effective illumination. High-pressure mercury lamps placed 80 cm above the plants can also be used, offering a light intensity of 0.8–1 kilolux. Lighting should be done after sunrise, typically for 2–3 hours daily, and extended on cloudy days.
Another effective method is using reflective screens made of aluminum-coated polyester film. These screens, 2 meters wide and 3 meters long, hung from the top of the posts down to the ground, can increase ground-level light by 40–43% and raise the temperature by 3–4°C. Laying silver-gray film or aluminum foil on the ground also enhances light reflection between plants, helping vegetables develop better color and preventing early leaf decay.
By implementing these strategies, growers can significantly improve light conditions in their greenhouses, leading to healthier plants, higher yields, and better-quality produce throughout the year.
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