NEXT-GENERATION, ENERGY-EFFICIENT, UNIFORM SUPPLEMENTAL LIGHTING FOR CLOSED-SYSTEM PLANT PRODUCTION

Abstract

Two relatively new, energy-efficient lamp types and light delivery systems for plant growth chambers were compared in matched 2.44 x 3.66 m walk-in plant growth chambers. The chambers were lit either by ninety-six 1.22 m long 54 W cool white HO T5 fluorescents arranged to cover the chamber ceiling, or by fourteen 315watt ceramic metal halide HID lamps arranged in two rows. The fluorescents were contained in twelve 0.61 x 1.22 m luminaires (Sunlight Supply Systems, Model 960202), each containing a reflector and eight tubes. The HID lamps were housed in custom-designed luminaires (Cycloptics All-Bright 315W) with reflectors mounted above the ceiling of the chamber, opening into the chamber. Light intensities were measured at the centers of ninety-six (8 x 12) uniformly sized grid squares in five planes below the ceiling, from 0.76 to 1.98 m down, with the walls and floor of the chamber below the plane of measurement made non-reflective by covering it with black material, and keeping the chamber empty and the door closed. Wattage required by the lamps and ballasts showed the HID system provided 40% to 60% more light per watt than the T5 system, with light distributed more uniformly in the three lowest planes. A T12 fluorescent system (forty-eight 215-watt VHO cool white lamps,) with which the growth chambers were previously lamped, was also compared to the T5 fluorescent and HID systems, using measurements for single quadrants of the chambers. This was found similar to the T5 system in light distribution uniformity, but inferior to both in terms of energy efficiency. The T5 system provided nearly four times more light per watt than the T12 system, and the HID system provided five and a half to more than six times more light per watt.