2018 ASHS Annual Conference

Artificial lighting is required in indoor production while it improves crop quality for year-round greenhouse production. Artificial light provided to plants is intercepted and transmitted by the canopy. The intercepted light is absorbed and a portion of the light is reflected back. Reflected light is wasted if plants do not reabsorb it. Extent of light reflection can further increase under stress conditions. Artificial light provided to plants can be significantly high, therefore it is important to minimize any wastage of provided light. Continuous monitoring of light absorption efficiency of plants can aid in reducing artificial light wastage. Currently available sensors (e.g., quantum sensors, spectral reflectance sensors) are not designed to measure light absorption efficiency of whole-plants. There is an urgent need to develop simple, accurate and affordable sensing techniques to estimate light absorption efficiency of plants. The objective of this study is to test the efficacy of image analysis technique for estimating light absorption efficiency of plants in CEA. For testing this technology, petunia (Petunia × hybrida L. ‘Easy Wave Red Velour’) seedlings were transplanted in a greenhouse maintained at 26/20°C (day/night) temperature and daily light integral (DLI) of 10-20 mol·m^-2·d^-1. Plants were subjected to optimum and stresses treatments including water stress, nitrogen stress and low light stress. Direct measurements such as, light absorption efficiency (ratio of absorbed to incident light intensity, PPF_a/i), photosynthesis rate (A) and shoot dry weight (SDW) were taken. A multi-spectral imaging station with image analysis software was used for image acquisition, plant pixel segmentation and plant reflectance measurement at different visible (450, 523, 591, 625, 660 nm) and near infrared (nir, 870 nm) wavebands. Mean reflectance of visible wavebands (R_VIS) from groups of plants was calculated and expressed as relative reflectance of light in visible wavebands (R_VIS/R₈₇₀). Results showed R_VIS/870 was inversely related to PPF_a/i and SDW. Petunia plants subjected to stress showed increased light reflectance (or absorbed less light) likely due to A under stress. These results indicate that image-based measurements (R_VIS/R₈₇₀) can be used to indirectly estimate light absorption efficiency in plants.