Reducing Lighting Energy Use in Controlled Agricultural Environments

Photometric simulations using both daylight and electric lighting were per -formed to compare the energy use of conventional high-pressure sodium (HPS) green-house lighting to that of light-emitting diode (LED) lighting. Photometric simulations of a hypothetical greenhouse were performed in three different geographic locations in the United States with widely different annual daylight availability: Albany, NY, Fairbanks, AK, and Phoenix, AZ. Simulation conditions included summer and winter, overcast and clear skies, and several lighting layouts and distributions. The analysis showed that, while maintaining the criteria levels of photosynthetic photon flux den-sity, lighting energy savings were primarily attributable to increased LED source effi- cacy rather than HPS. Secondary energy savings were attributable to the ability to continuously dim LED lighting in response to daily and seasonal changes in daylight. Despite options for LED luminaires with a slim form factor, reduced crop shading compared with larger conventional HPS luminaires did not result in significant light -ing energy savings.