Abstract
In plant factories, light is fully controllable for crop production but involves a cost. For efficient lighting, light use efficiency (LUE) should be considered as part of light environment design. The objectives of this study were to evaluate and interpret the light interception, photosynthetic rate, and LUE of lettuces under electrical lights using ray-tracing simulation. The crop architecture model was constructed by 3D scanning, and ray-tracing simulation was used to interpret light interception and photosynthesis. For evaluation of simulation reliability, measured light intensities and photosynthetic rates in a growth chamber were compared with those obtained by simulation at different planting densities. Under several scenarios modeling various factors affecting light environments, changes in light interception and LUE were interpreted. The light intensities and photosynthetic rates obtained by simulation showed good agreement with the measured values, with R2 > 0.86. With decreasing planting density, the light interception of the central plant increased by approximately 18.7%, but that of neighboring plants decreased by approximately 5.5%. Under the various scenarios, shorter lighting distances induced more heterogenetic light distribution on plants and caused lower light interception. Under a homogenous light distribution, the light intensity was optimal at approximately 360 μmol m−2 s−1 with an LUE of 6.5 g MJ−1. The results of this study can provide conceptual insights into the design of light environments in plant factories.
Highlights
Light is one of the most important environmental factors driving photosynthesis and growth.In this respect, full control of the light environments of plant factories with electrical lights (PFELs) has the advantages of stable year-round crop production, along with high productivity and quality [1,2,3,4].despite the continuous increase in the luminous efficacy of light sources such as LEDs [5], electrical energy consumption for lighting is a major burden for operating commercial PFELs
For each LED chip, spectral distributions of red and blue LEDs were measured with a spectroradiometer at 1-nm intervals for spectral power distribution (SPD) settings, and for physical light distribution (PLD), a Lambertian distribution with an angle of 60◦ was set
To match the photosynthetic photon flux density (PPFD) in the virtual growth chamber with the actual environment, a cylinder-shaped detector was modeled based on the quantum sensor dimension and placed on the datum point
Summary
Light is one of the most important environmental factors driving photosynthesis and growth.In this respect, full control of the light environments of plant factories with electrical lights (PFELs) has the advantages of stable year-round crop production, along with high productivity and quality [1,2,3,4].despite the continuous increase in the luminous efficacy of light sources such as LEDs [5], electrical energy consumption for lighting is a major burden for operating commercial PFELs. Light is one of the most important environmental factors driving photosynthesis and growth. In this respect, full control of the light environments of plant factories with electrical lights (PFELs) has the advantages of stable year-round crop production, along with high productivity and quality [1,2,3,4]. One solution for improving light use efficiency (LUE) is to optimize the light environment to maximize crop photosynthesis. To achieve this purpose, the light distribution in cultivating areas in PFELs can be modified by changing the spatial disposition of the light source when using the same light source or the same usable energy. Targeted lighting by adjacent LED positioning [8] and Agronomy 2020, 10, 1545; doi:10.3390/agronomy10101545 www.mdpi.com/journal/agronomy
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