GROWTH AND PHOTOMORPHOGENESIS OF PEPPER PLANTS UNDER RED LIGHT-EMITTING-DIODES WITH SUPPLEMENTAL BLUE OR FAR-RED LIGHTING

Light-emitting diodes (LEDs) are a potential irradiation source for in tensive plant culture systems and photobiological research, They have small size, low mass, a long functional life, and narrow spectral outp ut,In this study, we measured the growth and dry matter partitioning o f 'Hungarian Wax' pepper (Capsicum annuum L.) plants grown under red L EDs compared with similar plants grown under red LE;Ds with supplement al blue or far-red radiation or under broad spectrum metal halide (MH) lamps, Additionally, we describe the thermal and spectral characteris tics of these sources, The LEDs used in this study had a narrow bandwi dth at half peak height (25 nm) and a focused maximum spectral output at 660 nm for the red and 735 nm for the far-red, Near infrared radiat ion (800 to 3000 nm) was below detection and thermal infrared radiatio n (3000 to 50,000 nm) was lower in the LEDs compared to the MH source, Although the red to far-red ratio varied considerably, the calculated phytochrome photostationary state (phi) was only slightly different b etween the radiation sources, Plant biomass was reduced when peppers w ere grown under red LEDs in the absence of blue wavelengths compared t o plants grown under supplemental blue fluorescent lamps or MH lamps, The addition of far-red radiation resulted in taller plants with great er stem mass than red LEDs alone, There were fewer leaves under red or red plus far-red radiation than with lamps producing blue wavelengths , These results indicate that red LEDs may be suitable, in proper comb ination with other wavelengths of light, for the culture of plants in tightly controlled environments such as space-based plant culture syst ems.