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LEDs for Crop Production: Comparisons of Overhead vs. Intracanopy Lighting.   G.D. Massa, M.E. Mick, C.A. Mitchell. ALS NSCORT, Purdue Univ., West Lafayette, IN. 

   Electric lighting for crop production using red and blue LEDs is being investigated as a component of human life-support systems. Energy savings drives the development of crop-growth subsystems. Two reconfigurable LED arrays have been developed and are being tested in a side-by-side arrangement, with one array configured into a single overhead (OH) plane of light engines and the second array suspended vertically as separate intracanopy (IC) “lightsicles” among plants within the crop stand. Cowpea (Vigna unguiculata L. Walp PI IT87D-941-1 (D-941)) and dwarf pepper (Capsicum annuum cv. Triton) have been grown hydroponically using the two LED lighting arrays. Oedema has been observed on both crops. On cowpea, symptoms seem to be directly related to the amount of blue light received by the leaves, as well as to leaf age. For pepper, increasing the level or proportion of blue light did not reduce oedema. In spite of oedema, excellent cowpea vegetative growth has been observed under or within both arrays.  Also, oedema in peppers did not detrimentally affect flower or fruit formation.  This is our first observation of reproductive development using the IC configuration with LEDs as the sole source of crop lighting.  Electrical power usage per unit edible biomass produced was greater in the OH configuration, where mutual shading of lower leaves by upper leaves occurs.  In addition, the amount of water lost due to transpiration was higher with OH lighting.  These results indicate that, for planophile crops, IC lighting is a more efficient lighting geometry.  Work with a crop-canopy gas-exchange cuvette to accurately measure real-time canopy photosynthesis with IC LEDs is underway.  This will allow faster optimization of lighting preferences by a given crop and more detailed calculations to model mass flow through the biomass-production subsystem of a life-support system.  The LED lighting system is being developed jointly by NSCORT and Orbitec with input and assistance from R. Morrow, M. Bourget, and J. Emmerich of Orbitec.  This research was partially supported by NASA: NAG5-12686.