Comparison of spectral combinations of light emitting diodes for crop production

Abstract

Recent advances in Light Emitting Diode (LED) technology have made it possible for lighting arrays to provide user tunable wavelengths and adjustable intensities. LEDs also provide low radiant heat loads, have longer life spans, and improved energy efficiencies when compared with other light sources such as HID, incandescent and fluorescent lamps. Although currently expensive, these characteristics make LED lighting arrays suitable for their use in growth chambers. This study reports results from two experiments using LED arrays. The first compared a mixture of red (R; 640 nm) and blue (B; 450 nm) LEDs (RB) with a mixture of red, green (G; 540 nm), and blue LEDs (RGB). The second experiment looked at the effect of far red light (Fr; 725nm) on mass partitioning in the plants by comparing a mixture of RGB+Fr light with RGB lighting. In all cases the photosynthetically active radiation (PAR) was equivalent and the effects of spectral quality were compared against compact fluorescent lamps. Fluorescent lamps are the primary light source in modern growth chambers, making their spectral quality a good control for these experiments. PAR was approximately 200 µmol m-2 s-1, and plants were grown under 20 hours of light, 4 hours of dark. Other environmental parameters were identical between chambers and experiments. The crop used in the evaluation of the various light qualities was radish (Raphanus sativum cv Cherry Belle). All LED light combinations demonstrated an ability to grow healthy plants similar to plants grown using fluorescent lighting. In the RGB versus RB experiment, there was little difference in the percentage of mass dedicated to edible radish biomass. However, the plants in the RGB chamber had more leaf area than the plants in the RB chamber. Plants growing under RGB+Fr partitioned significantly more biomass to the edible radish than plants grown under RGB.