ASHS 2015 Annual Conference

Energy efficiency and increased light spectrum control have begun to drive many plant growth facilities to switch from fluorescent light bulbs to light-emitting diodes (LEDs).  We were interested to learn whether seemingly equivalent conditions between fluorescent lights and LEDs were functionally equivalent for plant growth.  To test this, we fitted half of a walk-in chamber with LumiGrow Lumibar LED lamps (red, blue, and white lights) and maintained the other half of the chamber with the traditional fluorescent lighting (cool white bulbs).  Using Arabidopsis as a model system we measured plant growth traits in six genotypes selected for their light-sensitive phenotypes: the wild-type Columbia-0, and two natural accessions, Kondara and Knox18, with extreme and mild shade response phenotypes, respectively. Additionally, the light signaling mutants phyB, cry1/2, and hy5 were selected for their sensitivity to varying light conditions.  Plants were grown under four different light conditions at a PAR of approximately 150 micromoles/m2/sec where the light conditions were adjusted for different light ratios:  Red (R) 143 red, 0 blue, 7 white; High Blue (HB) 73 red, 80 blue, 7 white, Mid Red Blue (MRB) 113 red, 30 blue, 7 white, and fluorescent light (F).  In addition, plants were grown with the Maximum PAR (MP) output for the LED light, approximately 350 micromoles/m2/sec PAR where the light ratio was 75% red: 20 %blue: 5%white.  Our analysis of leaf size, shape, and number, as well as days to flowering, indicated differences in growth patterns between light conditions.  PAR-matched and maximum PAR LEDs also showed some phenotypic growth differences compared to fluorescent lighting.  However, the LED lighting did not cause the same temperature increase as fluorescent lights (~5 degrees Celsius cooler); many of the major growth differences might therefore be due to differences in temperature, rather than light.  Overall, our findings suggest no reason to delay a transition to LEDs, even for studies involving light signaling.