The 2012 ASHS Annual Conference

Light emitting diodes (LEDs) are an emerging versatile artificial light source offering many advantages over conventional artificial light sources, including high energy efficiency, long life, and especially the possibility to test out the effects of many different spectral combinations of wavelengths on plant growth and development. This could eventually allow determination of the ideal light emission spectrum for optimal plant growth, allowing for lighting system designs tailored to optimize plant growth while minimizing associated energy costs. The impact of the photosynthetic rate of two plant species under different wavelengths of LEDs is determined in this study. The photosynthesis rate verse LEDs at different wavelengths was analyzed. The 14 specific wavelengths of LED (405, 417, 430, 450, 470, 501, 520, 575, 595, 624, 633, 662, 680, and 700 nm) and 3 plants (tomato, lettuce, and petunia) were used in this study. The 14 specific wavelengths of LED were determined based on the unit design, LED availability and pigment absorption spectra. The LED array was controlled (current controlled) using a single channel controller to produce uniform intensity of specific wavelengths of light over the PAR spectrum.  Specifications of the controller is a 24VDC, 2.0A maximum, 48 watt unit with current selected and displayed (0°1.92ADC), automatic voltage control. The intensity of the LED lighting system was calibrated and measured before and after the test at canopy level using a spectroradiometer to determine wavelength width, intensity, and any changes that may occur during the test. The LED lighting system irradiated the plant with the carbon dioxide usage rate monitored until stabilization occurred (within 10 minutes). Carbon dioxide utilization rate was measured with the LI-COR LI-6400XT portable photosynthesis system, with photosynthesis rate normalized with leaf area. The plants were tested at irradiance levels consisting of 30 μmol•m^-2•s^-1. The measurements of tomato, lettuce and petunia to redefine the photosynthetically active radiation (PAR) curve are included. From our research we found photosynthesis, absorbance, quantum yield and action spectrum peaks in the range of 417 to 450 nm and in the range from 630 to 680 nm. This research will facilitate the improved selection of LEDs in the PAR spectrum.