Increasing the Yield of Lactuca sativa, L. in Glass Greenhouses through Illumination Spectral Filtering and Development of an Optical Thin Film Filter

With the increase in world population, the continued advances in modern greenhouse agriculture and plant growth practices are expected to help overcome the global problem of future food shortages. The next generation greenhouse design practices will need to address a range of issues, ranging from energy and land use efficiency to providing plant-optimized growth techniques. In this paper, we focus on investigating the optimum irradiation spectra matched to the lettuce species (Lactuca sativa, L.), commonly grown in greenhouse environments, in order to develop low-emissivity glass panes that maximize the biomass productivity of glass greenhouses. This low-emissivity glass passes the solar spectral components needed for crop growth, while rejecting other unwanted radiations. This could potentially lead to significant energy savings and other beneficial effects related to greenhouse climate control, in a range of climates. The experimental results show that substantial biomass productivity improvements in lettuce (up to approximately 14.7%) can be attained by using spectrally optimized illumination, instead of white light illumination. This optimized wavelength is then demonstrated as being used to develop an advanced metal-dielectric thin-film filter that produces the optimized illumination spectrum when exposed to sunlight.