Estimation of supplemental lighting requirements of greenhouse crops based on canopy light interception using 3D plant models and ray-tracing simulation

Recently, crops are being cultivated in greenhouses with higher side-height and planting density to increase the yield. Accordingly, the distance between crops decreased, causing light deficiency in the crop canopy, and requiring supplemental lighting to compensate light deficit. In addition, the daily light integral (DLI) is commonly used as an indicator representing the light environment within crop canopy. However, in the inter-canopy lighting method, DLI cannot be used for that purpose in the greenhouse because the light emitted from the light source is transmitted to the middle and bottom leaves. The objective of this study is to estimate the supplemental lighting requirements of greenhouse crops based on canopy light interception using 3D plant models and ray-tracing simulation. Three-dimensional models of sweet pepper and tomato plants at three different growth stages were constructed by a 3D scanner. In simulation, HPS lamps were arranged above the crop canopy, and LED lamps were located at the middle of the canopy. The light distribution on the crop surface was calculated through ray-tracing simulation. To reflect the external light environment according to the growth stage, the light intensities were set to September, November, and January, respectively. The accumulated light at the top of the canopy showed a linear relationship with the accumulated light interception on the surface of the canopy. The accumulated light interception of sweet pepper and tomato plants by growth stage could be converted to corresponding DLI values. This method can be used as a basic technology for supplemental lighting control in greenhouses.