Justificación de la asignación de herramientas a los cursos

Greenhouse polymer films are of tremendous interest as North American consumers are demanding fresh fruits and vegetables that are disease, insect and blemish free. The ability to offer fresh, safe produce year round is made possible through the use of commercial greenhouses. The recent significant growth of greenhouse operations in Ontario is utilizing plastic films, which account for over 80% of greenhouse coverings. Over the past 40 years remarkable progress has been made in terms of the use and quality of greenhouse technology through the development of innovative plastic greenhouse covers. Greenhouse light quality manipulation has been shown to reduce energy requirements by up to 40%, virtually eliminating the need for forced ventilation in greenhouses. By spectral light manipulation, most commonly shown through light- emitting diode (LED) use, plant heights can be controlled, and both water usage and

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disease growth minimized. But, LED approaches would be extremely capital and energy intensive for commercial operation. Greenhouse cultivation is reported as the most intensive form of biomass production per unit of cultivated area with up to 10 times superior than that of a field crop [46]. By better understanding how to “tune” the effects of light and heat through greenhouse plastics using advances in nanotechnology we can both lower energy and water costs significantly, and boost biomass production.

Light outside the visible region also influences the plant growth. The ultraviolet component of solar radiation (especially 200-380nm) has been shown to degrade crops, and support harmful insect behavior causing damage to crops [47-49]. Insects have different optical photoreceptors for different bandwidths of light. Wavelengths in the UV region encourage specific insect behaviour such as orientation, navigation, host finding and feeding. Furthermore these pests and parasites can act as vectors for several harmful viruses. UV radiation absorbed by the polymer films also causes photochemical degradation of the films by leading to bond cleavage and depolymerization [23]. Commercially available UV stabilizers, such as benzophenones, benzotriazoles, nickel quenchers, hindered amine light stabilizers (HALS) have shown prevention of crop damage from pests and their diseases by filtering out much of the UV component from the plant’s light environment [48, 50-52]. However, little information is available about their incorporation into the polymer matrix. In addition, uniform distribution, long term stability, transparency of the films, and lowering costs are still major concerns [53]. Polymer films with QDs offer a useful and promising approach to improve solar energy harvesting, as QDs can efficiently convert undesirable higher energy UV radiation into desirable lower energy visible lights [24].

Commercial greenhouse covering materials posses a range of characteristics and properties targeted to specific spectral transmittance and energy functions. There are three main types of greenhouse films commonly available in the Ontario market, referred to as direct light, diffused light, and thermic films.

Figure 1.3. Schematics showing the direction of absorbed and reflected light light films (b) diffused light films, and (c) thermic films.

Direct light films characterized by high light transmission and clarity with low haze values allow for maximum light transmission of PAR

light required for photosynthesis into direct and diffused components

prevents plant burning, it reduces shadows and ensures more uniform distribution of light, so that it reaches even the lower parts of plants

photosynthetic rate and quality of harvest of diffusion depends on the c

For instance, during winter months and cloudy days, films with medium to low diffusion are preferable [54].

In addition to light, heat plays an important role in

allowing them to absorb significantly more infrared radiation. This reduces the transmission of long-wave infrared and thermal radiation from inside a greenhouse to the outdoors, causing significant radiative heat losses

available thermic films suffer from a loss of transparen spectrum which is important for the photosynthesis process

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Schematics showing the direction of absorbed and reflected light light films (b) diffused light films, and (c) thermic films.

characterized by high light transmission and clarity with low haze values allow for maximum light transmission of PAR (photosynthetic active radiation) light required for photosynthesis. Whereas, diffused light films split the

components. Light diffusion offers a moderate cooling effect, it burning, it reduces shadows and ensures more uniform distribution of light, so that it reaches even the lower parts of plants resulting in both a

tic rate and quality of harvest [54]. The choice of the most appropriate level of diffusion depends on the climate of the area, the crop and the season(s) of growing. For instance, during winter months and cloudy days, films with medium to low diffusion

is another significant environmental factor for plant growth and plays an important role in plant development. Thermic films contain thermal additives bsorb significantly more infrared radiation. This reduces the wave infrared and thermal radiation from inside a greenhouse to the significant radiative heat losses [55, 56]. However, commercially available thermic films suffer from a loss of transparency in the visible region of the solar spectrum which is important for the photosynthesis process [47].

Schematics showing the direction of absorbed and reflected light for (a) direct

characterized by high light transmission and clarity with low haze (photosynthetic active radiation) split the incident light Light diffusion offers a moderate cooling effect, it burning, it reduces shadows and ensures more uniform distribution of in both a higher The choice of the most appropriate level limate of the area, the crop and the season(s) of growing. For instance, during winter months and cloudy days, films with medium to low diffusion

is another significant environmental factor for plant growth and Thermic films contain thermal additives bsorb significantly more infrared radiation. This reduces the wave infrared and thermal radiation from inside a greenhouse to the . However, commercially cy in the visible region of the solar

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