LED Lighting Strategies

Our lab, has formed a collaborative research agreement with Orbitec to research and develop reconfigurable Light-Emitting Diode (LED) plant lighting systems. The purpose of this research is to substantially reduce the power requirements for growing plants in controlled environments. Power reduction will be necessary for both earth- and space-based controlled environment agriculture. We have developed two strategies to meet these goals using "light engines"- chips containing multiple, densely arrayed red, blue, and green LEDs.

Intracanopy Lighting

Intracanopy lighting is designed for "planophile" crops that orient their leaves perpendicular to an overhead light source and close the canopy, thus shading lower leaves. This growth habit, therefore, primarily relies upon leaves on the top or side of the canopy for photosynthesis, and plants will often shed the shaded leaves. Cowpeas are an example of a planophile crop. Intracanopy lighting utilizes the reconfigurable array as several independent "lightcicles". These linear LED strips hang vertically within the crop canopy, and each strip will contains 20 light engines that can be switched on or off incrementally as the plants grow. Thus, this system illuminates a larger percentage of plant leaves than traditional overhead lighting, and saves power by lighting only spaces where leaves occur.

HELIAC

HELIAC, High Efficiency Lighting with Integrated Adaptive Control, is the name of an SBIR granted to Orbitec to develop the automated plant detection system and LED switching system that will allow full functionality for the LED lighting array. Flashing green LEDs and photodiodes will allow detection of the presence or absence of a leaf in front of individual light engines, regardless of orientation. Custom software will integrate these signals to automatically switch on or off light engines to keep pace with photosynthetic organs as plants grow. Thus, only areas where photosynthesis is occurring will be lit, and power can be conserved.

Close Canopy Lighting

Close-Canopy lighting is designed for "erectophile" crop stands that position their leaves parallel to an overhead light source or rosette plants that form a central axis. As these plants grow, additional leaves expand from the central axis until space between plants is filled. The rosette habit is seen in crops such as lettuce, while the erectophile habit describes crops such as wheat. Close-Canopy lighting will utilize a horizontal configuration such that strips are placed edge-to-edge to create a flat "glowplate". The glowplate will be maintained in close proximity (<1") to the tops of the plants. Close-canopy lighting requires HELIAC technology so that individual light engines will be energized only above seedlings, and as plants expand additional light engines will be activated in expanding rings. The height of the glowplate will be adjusted to keep pace with plant growth as well. The use of low power is what will permit the close spacing of the LEDs to plant tissues in either configuration.

Gas Exchange System

Working with designers at the Purdue Central Machine Shop we have designed a canopy gas exchange cuvette system to run with various configurations of intracanopy LED lightcicles. This system will allow real time measurements of photosynthesis in response to changes in light quantitiy, light quality, temperature, humidity, and CO2 level as a crop matures. The cuvette is in the final stages of design, and construction will begin shortly.