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Testing of the HELIAC 2 Plant Detection and Lighting System.     G.D. Massa¹, C.M. Bourget², R.C. Morrow² and C.A. Mitchell^{1       1}Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN and ²Orbital Technologies Corporation, Madison, WI.

   As part of a Phase 2 SBIR awarded to Orbital Technologies Corporation (ORBITEC) we have developed HELIAC, High Efficiency Lighting with Integrated Adaptive Control.  This LED lighting system can be configured for overhead or intracanopy plant lighting.  Automated adaptive controls allow the lighting system to detect the position of plant leaves through reflectance of green light, and algorithms integrate these signals into a lighting pattern that changes automatically in response to plant position and leaf area.  In this way, minimum electrical energy and crewtime are used to produce the optimum crop yield. 

   Initial testing at Purdue University involved three planophile species with the lights in an intracanopy (vertical) configuration.  Tomato and sweetpotato plants were grown from cuttings and cowpea plants were grown from seeds.  A variety of different flash patterns were run at various settings of green light intensity, with adaptive threshold settings to compensate for background noise.  These data allowed us to determine preliminary settings for a full crop growth cycle using cowpea.  As cowpea plants grew, settings and detection response were monitored and adjusted.  Similar studies were performed with lettuce, but in this instance the HELIAC system was reconfigured to an overhead (horizontal) lighting configuration.  This configuration was run in a close-canopy mode, with detection and switching keeping pace with leaf production and expansion.  We plan to separate the sixteen lightsicles in each HELIAC system into two discrete HELIAC sub-systems that can be run simultaneously. Tests will compare the consistency of the two systems and demonstrate the ability to conduct scientific experiments while light control is automated.  Results of these trials will highlight the potential energy-saving value of adaptive LED lighting for plant hardware in an advanced life-support system.  This work was supported by a NASA SBIR to Orbital Technologies Corporation.