A 3D Model of Illumination, Light Distribution and Crop Photosynthesis to Simulate Lighting Strategies in Greenhouses

A functional-structural model for a tomato crop, situated in a greenhouse, was developed to calculate the most efficient lamp (HPS, LED) positions and crop structure, with the objective to reduce energy consumption and improve light use efficiency. The model was built within the GroIMP platform and written using the dedicated modelling language XL. The entire production system is described as a 3D scene including a virtual greenhouse with the crop and light sources (natural light and lamps). The pathways of individual light rays were modelled multi-spectrally with an inversed path tracer. Plant organs (leaves, internodes, flowers, fruits) are the basic units of the multi-scaled, fully object-oriented model. Surface textures and colours were included for all 3D objects. For the current objective a static 3D mock-up of an existing crop was used. Measured 3D distribution pattern and spectrum of light emitted by the lamps were fed into the model. The modelled horizontal light distribution agreed well with measurements. Effects of different positions, reflector types, and spectra of lamps, and plant architectural and optical properties on light distribution and photosynthesis were evaluated. In total 10 illumination scenarios were simulated to quantify crop absorption and loss of light. In summary, a more efficient illumination strategy was predicted when the light was more focused on the crop by lamp reflectors, at inter-lighting (LEDs), and with a reflecting screen above the lamps. The inter-lighting strategy also resulted in a relative increase of light intercepted by fruit and stems relative to lighting from the top of the crop.