Plant growth and sensing using high-brightness white and red light-emitting diodes

Summary form only given.It is well known chlorophyll, which is contained in green leaves of plants, performs photosynthesis. The chlorophyll absorbs selectively blue and red light components in the sunshine. The blue absorption region is 430-450 nm and that of red is 650-670 nm. This suggests that it is possible to cultivate green plant under a blue and red composite light. The authors succeeded in the growth of plant (lettuce seedlings) with healthy morphology using blue (450 nm) and red (660 nm) high-brightness LEDs in 1994. In 1996, they developed a novel method to grow a plant by a composite white light source composed of red, green and blue (RGB) LEDs and further to measure the condition of plant growth using the LED panel itself. According to the method, all the RGB LEDs are lighting in the growth mode and only G-LEDs are lighting in the sensing mode. The growth can be monitored by the DC photovoltage generated in the red LEDs circuit by the reflected green light from the leaves of the plant. This method was very unique and smart, however there were weak points: (1) complexity in manufacturing the RGB-LED circuits, (2) influence of light and circumstances. Here the authors present a new plant growth/sensing system using white and red high-brightness LEDs.