## 1 Introduction  
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]. Meanwhile, 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. Electrical energy occupies the largest part of the operation cost, and most of the electrical energy consumption comes from lighting rather than other energy loads, such as heating, cooling, or dehumidification, in PFELs [6; 7]. 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 concentration on effective cultivation areas have been shown to reduce electrical energy loss [9], and supplementary upward lighting for lower light-scarce leaves increases the yield of lettuce, which results in an increase in LUE [10]. However, despite the validity of lighting modifications in improving LUE, there have been few studies concerning the application of this improved lighting method to PFELs, possibly due to the large time, labor and financial cost required for actual cultivation in various light environments. Although previous studies have shown the effect of lighting modification on growth and yield, the effects on intermediate processes between lighting and plant growth, such as light interception and photosynthesis, remain unknown. To clarify the potential effect of lighting modifications on growth and yield, these processes should be considered. The use of a modeling approach with functional-structural plant models (FSPMs), which describe the plant response to environmental factors by integrating physiological sub-models and plant structure models, can provide good explanations [11; 12]. To link the change in the light environment to LUE, various elements should be considered, such as spatial light distribution in the cultivation space, light interception of the plant canopy, and physiological processes that convert light interception to photosynthesis. Several studies have adopted FSPMs to describe these elements, especially by combining ray-tracing simulation with virtual plant models [13; 14; 15; 16; 17; 18]. In elucidating the influence of light environments on light interception, precise plant structures for virtual plant models are considered to be one of the crucial factors [19]. [PERSON] [18] reported that the light interception and photosynthesis of structurally inaccurate leaf models with low curvature were overestimated compared to those of accurate models. Thus, virtual plant models need to precisely reflect the actual structure to ensure the reliability of prediction. In this respect, image-based 3D reconstruction, which directly extracts the plant structure from 2D or 3D images, is widely used to construct elaborate virtual plant models [20; 21; 22]. Meanwhile, despite the importance of the light environment design and improvement of LUE, few studies have introduced FSPMs to interpret light interception in PFELs. Recently, [PERSON] [23] simulated various lighting angles and spectral power distributions for electrical lights in a plant growth chamber and explicitly found the validity of ray-tracing simulation in PFELs. However, the uses of structurally accurate plant models and interpretations of LUE under various light environments in PFELs are still limited.