<p>  </p> <p>With the rapid growth in population and urbanization, an increased supply of fresh, nutritious, and safe food in urban areas is required. Relying solely on conventional agriculture for food production can be risky due to climate change and decreasing natural resources (i.e., water, and arable land). Vertical farming (VF) involves growing food crops (primarily leafy greens and small-statured fruits) at multiple levels in controlled environments with less land and water inputs. However, high operational costs have resulted in low-profit margins in VF, which are challenging the economic sustainability of the VF industry. With the present VF technology, it may be difficult to significantly reduce the operational costs. Therefore, maximizing the wholesale value of produce, which is determined by the total yield and sale price per unit quantity (or crop value), is critical for increasing profits in VF. In this research, the overall goal is to increase lettuce growth, nutritional quality, and food safety by optimizing the light quality of light-emitting diodes (LED) in VF to increase the whole value of produce and thus increase the VF profits. The objectives of the research were to (i) study the independent and interactive effects of monochromatic wavebands of light from UV-A (365 nm) to far-red (750 nm) on lettuce growth and nutritional quality; (ii) identify the effects of substituting moderate proportions of UV-A and a high proportion of UV-A coupled with far-red light in growth lighting on lettuce growth and nutritional quality; (iii) study the effects of lettuce cultivars and UV LED light on the survival of <em>E. coli</em> O157:H7 on lettuce in VF production.</p> <p>In the first study, we investigated the effects of different wavebands of light ranging from UV-A (370 nm) to far-red (733 nm), both independently and in combination with commercial growth lighting on lettuce growth, incident light-use efficiency (LUEinc), and levels of phytochemicals. Results showed that the monochromatic wavebands 389 and 733 nm had positive interactions with the growth lighting on lettuce. In addition, results also indicated that UV-A light at a peak wavelength of 389 nm could potentially increase phytochemical concentrations. In the second study, the effects of 40% UV-A (UV 389 nm) and 60% UV-A (UV 389 nm) plus 10% far-red (FR 733 nm) light for growth light during the plant stationary growth stage on lettuce biomass and biosynthesis of phytochemicals were examined. Results showed that substituting UV-A for 40% growth lighting during the plant stationary growth stage for seven days resulted in significantly increased levels of beta-carotene and phylloquinone in lettuce while slightly lowering lettuce growth. And the addition of far-red light to UV-A did not result in the expected increase in vegetative growth, while the levels of phytochemicals were not affected. In the third study, we first investigated the effects of four lettuce cultivars, including oakleaf, romaine, butterhead, and leaf lettuce on the survival of <em>E. coli</em> O157:H7 gfp+. Results showed that leaf lettuce had the lowest while oakleaf and romaine had the highest concentrations of <em>E. coli</em> O157:H7 gfp+ when sampled on days 2 and 7 after the inoculation, and on day 7 after harvest and storage at 4 °C. Then we examined the feasibility of supplementing UV-A, UV A+B, and UV A+C during plant growth stages to reduce <em>E. coli</em> O157:H7 gfp+ contamination on lettuce. Our results indicated that only the UV A+C light at an intensity of 54.4 μmol·m-2·s-1 for 15 minutes per day after inoculation reduced <em>E. coli</em> O157:H7 gfp+ contamination by 0.33 log CFU·g-1 without affecting plant growth and levels of phytochemicals.</p> <p>The outcomes from our research suggested that the interactive effects of monochromatic wavebands should be considered in developing light recipes. In addition, VF growers who are interested in improving the nutritional phytochemical levels such as beta-carotene and phylloquinone in lettuce while maintaining growth should consider adding a moderate proportion (< 40%) of near-blue UV-A (i.e., 389 nm) radiation during the plant stationary growth phase to growth lighting. However, shorter wavelengths of UV-A radiation are not recommended due to their negative effects on plant growth and high economic cost. For growers who are at high risk of <em>E. coli</em> O157:H7 contamination, it is suggested that growing leaf lettuce and supplementation of UV A+C LED light during the plant-growth period should be considered to reduce the <em>E. coli</em> O157:H7 contamination levels.</p>

<p>Vertical farming (VF) as a newer sector of controlled-environment agriculture (CEA) is proliferating as demand for year-round, local, fresh produce is rising. However, there are concerns regarding the high capital expenses and significant operational expenses that contribute to fragile profitability of the VF industry. Enhancing resource-use efficiency is a strategy to improve profitability of the VF industry, and different approaches are proposed in the three chapters of this dissertation. LEDs are used for sole-source lighting in VF, and although they recently have significantly improved electrical efficiency and photon efficacy, the Lambertian design of the illumination pattern leads to significant loss of obliquely emitted photons beyond cropping areas. In chapter 1, close-canopy lighting (CCL) is proposed as one effective energy-saving strategy, through which unique physical properties of LEDs were leveraged, and two CCL strategies (energy efficiency and yield enhancement) were characterized at four different separation distances between light-emitting and light-absorbing surfaces. Dimming to the same light intensity at all separation distances resulted in the same biomass production while significant energy savings occurred at closer distances. Significantly higher light intensity and yield were achieved under closer separation distances in the yield-enhancement strategy for the same energy input. The energy-utilization efficiency (g fresh/dry biomass per kWh of energy) was doubled in both scenarios when the separation distance between LED emitting surface and crop surface was reduced maximally. At reduced separation distances, the chance of photon escape from growth areas is less, and canopy photon capture efficiency is improved.</p><p>Optimizing environmental conditions for indoor plant production also helps improve resource-use efficiency for the nascent vertical-farming industry. Although significant technical advancements of LEDs have been made, use of efficient far-red (FR) LEDs has yet to be exploited. As a recent proposed extension to traditional photosynthetically active radiation (PAR, 400-700 nm), FR radiation (700-750 nm) contributes to photosynthesis as well as photomorphogenesis when added to shorter wavelengths of traditional PAR. However, the interaction of FR with other environmental parameters such as CO2 is less studied. In chapter 2, the interaction effect of four FR fluxes (as substitution for red) in combination with three different CO2 concentrations were investigated at three distinctive stages of young-lettuce production. The highest biomass achieved at all stages occurred at 800 mmol mol-1 CO2 compared to 400 and 1600 mmol mol-1. A photomorphogenic effect of FR to promote leaf length was pronounced at the earliest stages of development, at which FR did not contribute to higher biomass accumulation. At more developed stages, 20 mmol m-2 s-1 of FR substituting for red contributed to biomass accumulation similar to shorter wavelengths of traditional PAR, whereas higher fluxes of FR in the light recipe resulted in undesirable quality attributes such as longer leaves.</p><p>Optimizing environmental conditions for indoor production with emphasis on light intensity and CO2 concentration at four distinctive stages of lettuce production was investigated in chapter 3. Utilizing the Minitron III gas-exchange system, light and CO2 dose-response profiles were characterized at four distinctive crop-development stages through instantaneous gas-exchange measurements at crop level. At all developmental stages, as CO2 concentration increased, photosynthesis increased up to 500 mmol mol-1, above which the incremental rate of photosynthesis was reduced. Light-dose response profiles were characterized at 400 or 800 mmol mol-1 CO2, and as light intensity increased, photosynthesis increased up to 650 mmol m-2 s-1. However, when instantaneous power (Watts) consumed for lighting was taken into consideration, power-use efficiency as the ratio of output photosynthesis increment to input power increment (to increase light intensity), decreased at higher light intensities. Vertical farming as a nascent and growing industry is facing limitations including marginal and even elusive profitability. Optimizing environmental conditions for indoor plant production such as these will help improve resource-use efficiency and profitability of the vertical farming industry.</p>