Estimation of supplemental lighting efficiency based on PPFD distribution on the canopy surface

Abstract

Criteria for evaluation of the efficiency of supplemental lighting based on photosynthetic photon flux density (PPFD) distribution on a canopy surface under artificial light were proposed, and the possibility of a reflection-image-based estimation of PPFD distribution on the canopy surface was discussed. Reflection images of plant canopy surfaces under various artificial lighting conditions were acquired from three directions with a digital camera equipped with a blue-green band-pass filter. PPFD was measured at one point on the canopy by a quantum sensor simultaneously with imaging, and the result was used to determine a regression model to estimate PPFD on leaves from pixel values of the image. The histogram of pixel values after gamma correction was converted into a PPFD histo- gram. The histogram pattern depended on the light source and canopy structure. Histograms estimated from images could depict the differences, showing mean values and coefficients of variation (CV) close to the measured values. Integrated PPFD over all illuminated leaves per unit power consumption (IPPC) was calculated from the histogram as a criterion for evaluating the efficiency of supplemental lighting. The efficiency also depended on the light source, canopy structure, and distance from the canopy surface. The estimated efficiency approximately agreed with the measured value in each case. These results suggest that reflection-image-based estimation of light intensity distribution can be used for simple evaluation of the efficiency of supplemental lighting.