Modern glasshouses, as essential facilities for agricultural production, rely heavily on their covering materials to create optimal growing conditions for crops. The two primary types of greenhouse coverings—plastic and glass—differ significantly in terms of light transmission, thermal insulation, and ultraviolet (UV) radiation transmission. UV radiation is a critical component of the solar spectrum; while moderate exposure benefits plant growth, excessive UV can cause crop scorching or disease. Therefore, understanding how different covering materials block UV radiation is vital for the design and management of modern glasshouses.
1. UV Transmission Characteristics of Modern Greenhouse Coverings
1.1 UV Blocking by Glass in Modern Glass Greenhouses
Glass is the primary covering material in modern glass greenhouses, and its UV transmission varies by type. Standard float glass blocks most short-wave UV radiation (UV-B and some UV-A) but allows long-wave UV (UV-A) to pass through. Low-iron ultra-clear glass, on the other hand, transmits more UV, which may be detrimental to certain sensitive crops. In recent years, some modern glass greenhouses have adopted coated or laminated glass to further reduce UV transmission and optimize growing conditions.
Research indicates that standard glass blocks approximately 90% of UV-B (280–315 nm) and 50–70% of UV-A (315–400 nm), while tempered and laminated glass offer even greater UV blocking. As a result, modern glass greenhouses provide a controlled UV environment, making them ideal for high-value crops sensitive to UV, such as certain flowers and vegetables.
1.2 UV Blocking by Plastic in Modern Glasshouses
Plastic-covered greenhouses are widely used in modern agriculture, with materials typically including polyethylene (PE), polyvinyl chloride (PVC), and ethylene-vinyl acetate (EVA). Compared to glass, plastic films generally transmit more UV radiation, particularly standard PE films, which allow significant UV-A and some UV-B to pass through. However, advancements in plastic film technology have led to the development of UV-blocking films, which incorporate UV absorbers or reflective layers to significantly reduce UV transmission.
Different types of plastic films vary in UV management:
Standard PE film: High UV transmission (often over 80%), suitable for crops that benefit from UV exposure.
UV-blocking film: Blocks over 90% of UV-B and a portion of UV-A, commonly used in nurseries to reduce disease risk.
EVA film: Offers good light transmission but moderate UV blocking, falling between standard PE and specialized UV-blocking films.
Thus, managers of plastic greenhouses must select the appropriate covering material based on crop requirements to balance light exposure and UV protection.
2. Comparison of UV Management in Glass and Plastic Greenhouses
The choice between glass and plastic in modern glasshouses affects not only UV transmission but also cost, durability, and climate adaptability.
Property | Glass Greenhouse | Plastic Greenhouse |
UV-B Blocking | High (>90%) | Variable (low in standard film, high in UV-blocking film) |
UV-A Blocking | Moderate (50–70%) | Low (standard film) to moderate (UV-blocking film) |
Light Transmission | High (varies by glass type) | High (but degrades over time) |
Lifespan | Long (>10 years) | Short (3–5 years) |
Cost | Higher | Lower |
From a UV management perspective, modern glass greenhouses are better suited for high-value crops requiring strict UV control, while plastic greenhouses offer greater flexibility, allowing adjustments in UV exposure through film selection.
3. Optimization Strategies for UV Management in Modern Glasshouses
3.1 Covering Material Selection
For UV-sensitive crops (e.g., tomatoes, cucumbers), UV-blocking films or coated glass are recommended.
For crops that benefit from UV exposure (e.g., some medicinal plants), standard plastic films or ultra-clear glass may be used.
3.2 Smart Light-Adjustment Technologies
Some modern glasshouses employ light-regulating films or adjustable glass to dynamically control UV transmission based on crop growth stages.
3.3 Supplemental UV Lighting
In regions with insufficient natural UV (e.g., high-latitude greenhouses), UV-LED supplementation can be used to enhance secondary metabolite production in plants.
4. Conclusion
Greenhouse coverings (plastic and glass) vary in their ability to block UV radiation. Modern glass greenhouses typically provide higher UV blocking, making them suitable for precision crop management, while plastic greenhouses offer greater flexibility through material selection. In modern agriculture, choosing the right covering material and optimizing UV management can improve crop yield and quality, supporting sustainable greenhouse cultivation.
