High-power LED illumination system for photosynthetic research on potted plant canopies

摘要

The high energy efficiency and radiant flux of high-power LED devices has lead to many new applications of LED lighting. Within the more production oriented applied plant research, there is a need for illumination systems that ensures a high irradiance, spectral control and homogeneous illumination of a large plant canopy to ensure reproducible results over long term measurements. A new high power LED illumination system is presented. It has been designed and developed for illumination of a plant canopy area of 60 x 80 cm2 in a climate chamber where photosynthesis of the whole canopy can be measured. The LED system extends the precise control of the chamber climate with computer control and long term stability of the irradiance and spectral composition of the illumination. High-power red and blue (at 455 and 639 nm) LED devices have been chosen that coincides with the absorption peaks of chlorophyll. The illumination system allows for a maximum irradiance of 6.3 W/cm2 corresponding to a photosynthetic photon flux density (PPFD) of 300 μmol m~(-1) s~(-1). The spectral composition of the light given by the ratio of blue photons compared to the total number of red and blue photons can be adjusted from 0-40 % keeping the irradiance at a constant level. Spectroradiometric 2D grid measurement at the plant top level shows homogeneity of ± 5% of the irradiance and ± 5% of the spectral distribution, over almost the entire canopy area. Initial experiments carried out on Chrysanthemum plants showing the dependence of the photosynthesis on blue light fraction is presented and discussed.