Developing a new supplemental lighting device with ultra-bright white LED for vegetables

Abstract

It has been proved that monochromatic or compound light-emitting diode (LED) or laser diode (LD) can promote the photosynthesis of horticultural crops, but the promotion of polychromatic light like white LED is unclear. A new type of ultra-bright white LED (LUW56843, InGaN, &nullset; 5 mm, 150mW, 15000 mcd, wavelength range: 400~720 nm) was selected to make up of the supplemental lighting panel (200×300 mm²), on which LEDs were evenly distributed with 90 branches. Drive circuit was selected to power and adjust light intensity. System performance including temperature rise and light intensity under different currents and vertical distances were tested. Photosynthesis of sweet pepper and eggplant leaf under white LED was measured with LI-6400 to show the supplemental lighting effects. The results show that LED system can supply the maximum light intensity of 300 &mgr;mol/m² <b>.</b>s at the distance of 100 mm below the panel and the temperature rise is higher over 13 °C on the surface of LED encapsulation, but hardly changes 100 mm far away the panel. For both of the two vegetables net photosynthetic rate became faster when white LED system increased light intensity. Compared with sunlight and plant growth fluorescent lamp, white LED's promotion on photosynthesis is inferior because its spectra is unreasonable with more blue light and less red light. Therefore, the unreasonable spectra become the major constraint of its application, but the potential of white LED application into vegetable crop production is prospective.