UV-OPEN vs UV-CLOSED Greenhouse Film
Understanding UV wavelengths, pollination and Australian growing conditions
Knowledge Centre | Greenhouse Film Science
UV-OPEN does not mean all ultraviolet light passes through. UV-CLOSE does not mean every UV wavelength is completely blocked. These terms describe how a greenhouse film transmits selected parts of the UV spectrum, and that distinction can matter for crops, pollinators and growing conditions.
The right question is not simply "UV-OPEN or UV-CLOSE?" It is "which wavelengths, how much transmission, and for what growing purpose?"
First, understand the ultraviolet spectrum
The UV spectrum is not one single band
Figure 1. UV-C (100–280 nm), UV-B (280–315 nm) and UV-A (315–400 nm). Diagram shows the 250–700 nm portion for readability.
UV-C (100–280 nm) from sunlight is almost entirely absorbed before reaching the Earth’s surface. UV-B (280–315 nm) partly reaches the surface and can influence plant stress responses and secondary metabolites. UV-A (315–400 nm) reaches the surface in much greater amounts and is relevant to insect visual perception and some plant responses. The UV bands have different biological roles: “UV” is not a single uniform input.
What do UV-OPEN and UV-CLOSE actually mean?
In greenhouse-film marketing, UV-OPEN generally refers to a film engineered to transmit more of a selected UV range, often part of UV-A. UV-CLOSE generally refers to a film engineered to suppress selected UV wavelengths. Neither label, by itself, specifies a universal wavelength cutoff or a guaranteed percentage of transmission.
Figure 2. ILLUSTRATIVE ONLY: conceptual spectral-transmittance profiles, not measurements of SunLite or any supplier product. Real curves must come from a spectrophotometer test on the finished film.
Two films both labelled UV-OPEN can have different cutoff wavelengths and different transmission within UV-A. Likewise, two UV-CLOSE products can differ substantially. A meaningful comparison should show spectral transmittance versus wavelength, preferably including the 280–400 nm region and the relevant visible-light range.
Why can UV transmission matter for pollination?
Bees perceive light differently from humans: their visual systems include sensitivity to ultraviolet, blue and green wavelengths. Many flowers display UV patterns that can act as visual cues. UV-A transmission through a covering can therefore be relevant to flower recognition and some pollinator behaviours.
However, pollination is not controlled by UV alone. Species differences, visible light, polarisation patterns, greenhouse layout, temperature, humidity, floral biology and colony management can all affect behaviour. Bumblebees and honeybees should not be treated as identical. A UV-OPEN label is not a guarantee of better fruit set.
UV-A can contribute to the visual environment used by pollinators. It is not an on/off switch for pollination.
Could strong Australian sunlight change the comparison?
Yes, as a physical possibility. The UV reaching a crop depends on outdoor spectral irradiance × film spectral transmittance (with additional effects from angle, scattering, structure and time of day). A location with stronger outdoor UV may deliver a similar total UV-A irradiance beneath a lower-transmission film compared with a weaker-UV location beneath a higher-transmission film.
Figure 3. Hypothetical arithmetic only: 20 W/m² × 60% = 12 W/m²; 40 W/m² × 30% = 12 W/m². These are not measured Australian site values or predicted crop outcomes.
But equal total UV-A energy does not imply identical biological effects: the wavelengths within UV-A may differ, and insects have wavelength-dependent sensitivity. Australia’s public UV Index is weighted for human sunburn risk; it is not a direct measure of the UV-A spectrum used by bees. Site-specific conclusions require actual irradiance and film spectra, followed by crop and pollination observations.
UV stabilisation is not UV blocking
Figure 4. Two separate design questions: protecting the polymer against UV ageing versus controlling UV transmitted tothe growing environment.
UV stabilisation helps the polyethylene film resist photo-oxidative ageing. UV blocking changes which wavelengths pass through the film. A UV-OPEN film can still be UV-stabilised for outdoor durability; a UV-CLOSE film is not automatically longer-lasting. UV absorber chemistry may contribute to both functions in some formulations, but the specifications must be evaluated separately.
How should Australian growers choose?
Crop and production objective: Is the priority pollination, plant morphology, colour development, pest management or a combination?
Pollination system: Which insect species is used, and is insect pollination essential for the crop?
Actual film spectrum: Request a finished-film UV transmission curve, not only the marketing label.
Site conditions: Consider local solar radiation, season, altitude, greenhouse design and other coverings.
Whole-film performance: Also evaluate PAR transmission, diffusion, thermal properties, anti-drip behaviour, UV durability and chemical resistance.
Field validation: Compare pollinator activity, fruit set, yield and quality under representative conditions before generalising results.
Common misconceptions
“UV-OPEN means 100% of UV passes through.” False. It refers to greater transmission in selected bands; actual percentages and cutoffs vary.
“UV-CLOSE blocks all ultraviolet light.” Not necessarily. The term alone does not define a complete 100–400 nm rejection profile.
“UV-CLOSE prevents bees from pollinating.” Too simplistic. UV affects some visual cues, but pollination depends on many factors and species.
“UV-OPEN is always best for berry crops.” Not established. Crop, pollinator, site and film spectrum determine suitability.
“A UV-stabilised film must be UV-CLOSE.” False. Polymer durability and crop-side spectral transmission are separate specifications.
Aus Crop Cover Insight
A greenhouse film should be treated as a selective optical material, not as a simple transparent oropaque barrier to UV. The most useful specification is a measured transmission curve paired with an understanding of the crop, pollinator and local growing environment.
Do not choose a UV film by the label alone. Choose it by the wavelengths that reach the crop, and the outcome you need.
Evidence and technical notes
CIE / ISO spectral conventions: UV-A 315–400 nm; UV-B 280–315 nm; UV-C 100–280 nm.
Bee colour vision: established ultraviolet, blue and green receptor classes; pollinator responses depend on species and environmental cues. See Briscoe & Chittka (2001), Annual Review of Entomology, “The evolution of color vision in insects.”
Greenhouse coverings and pollinator activity: effects are wavelength- and context-dependent; film-specific claims require spectral measurements and field trials.
Australian Radiation Protection and Nuclear Safety Agency (ARPANSA): the UV Index reflects erythemally weighted UV exposure, not a standalone UV-A measurement.
Figures 2 and 3 are explanatory illustrations, NOT supplier test data. Replace with SunLite finished-film spectral data before making quantified product claims.
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