[75]

Automated Plant Detection and Illumination Control System for an LED Based Lighting Array. J.C. Emmerich1, C.M. Bourget1, T.J. Clavette1, R.C. Morrow1, C.A. Mitchell2 and G.D. Massa2,  1Orbital Technologies Corporation, 1212 Fourier Drive, Madison, WI and 2Dept. of Horticulture & Landscape Architecture, Purdue University, West Lafayette, IN.

   Light emitting diode (LED) plant lighting systems utilizing an array of “Light Engines” are currently being designed and tested. Each light engine consists of a one inch square metallic substrate containing up to 132 LEDs, two photodiodes (for light measurement), and the associated interconnect printed circuitry. In the current design, the light engine may contain LEDs of up to five different wavelengths. The output of each wavelength within each light engine in the array may be individually controlled. An advantage of this approach is that it is possible to illuminate only the light engines positioned in front of or along side plant material and all other areas of the array may be turned off. In large plant growth systems this has the potential of significant power savings, especially when the plants are early in their development.

   The goal of this project was to develop and test a detection system utilizing the LEDs and on-board photodiodes to identify, by light reflectance, which light engines were in the proximity of plant material and should be energized. A linear array of twenty light engines was constructed and interfaced to a series of LED drive and photodiode output measurement circuits. Both manual and automated (microcontroller based) measurement and control capabilities were provided. Test variables included plant type and spatial location, illumination pattern, LED drive level and detection threshold.

   It was found that the development of an automated detection and control system was feasible. Plants were accurately detected at a distance of up to 10cm (greater distances may be possible but were not tested). The best overall illumination pattern was a single light engine energized with reflectance feedback provided by adjacent engines. This was especially true in growth environments utilizing reflective walls.