Application Of LED To Arabidopsis Thaliana Growth Light Source

As the fourth generation semiconductor light source, Light-emitting diode (LED) has many advantages such as high efficacy, long life time, low size, fast response, environment friendly, cold light source etc., which guarantee its broad application prospect in general lighting and agriculture lighting field. Monochromatic LED has better color purity and narrow wavelength band than that of traditional light sources, which makes them the idea light source for plant growth light research. As the development of the LED technology, the LED’s efficacy keeps increasing while its cost keeps declining. Because of its advantages in intelligent control system and merits stated above, there will be a boon for LED applications in facility agriculture field in the foreseeable future. Light intensity measurement difference between agriculture lighting and general lighting was firstly discussed. In order to study the growth characteristics of Arabidopsis under different light condition, two LED light control system are designed. Chlorophyll content and root growth characteristics under different red to blue light ratio (R/B) and different Photosynthetic Photon Flux Density (PPFD) were studied. A new concept of Photosynthetically Active Radiative Flux was introduced on the basis of the absorption spectrum of chlorophyll a and b. This concept can provide scientific references for the design of high efficacy, environmental friendly LED Iuminaires.In the first Arabidopsis growth experiment, dimming signal, which used to control the dimming level of the LED light modules, was realized by a resistant voltage divider circuit. Dominant wavelengths of the two monochromatic LED light sources are450nm and655nm respectively. After2d vernalization under4℃, Arabidopsis seeds are planted in the petri dishes and put into the experimental light environment for21d cultivation. The results show that:the germination rates of Arabidopsis under two light environments are the same of0.94; The chlorophyll content of Arabidopsis under Fluorescent light environment is half of that under LED light environment, which are0.15mg·g-1and0.32mg·g-1respectively; Under LED light environment, the chlorophyll content shows a slight decline when the R/B increase; Besides, there are obvious difference between stems, leaves and roots.The second Arabidopsis growth experiment, which is implemented to study the chlorophyll content, main root length etc. under fluorescent lamp light environment and LED light environment, is designed based on the results of the first one. A new RS485control system was employed. Dimming of the LED light source can be realized by using the computer program. Dominant wavelengths of the two monochromatic LED light sources are445nm and638nm respectively. The experiment results show that under the PPFD of about64μmol·m-2·s-1condition, the average chlorophyll content of Arabidopsis under LED light and that under fluorescent lamp light are1.52mg·g-1and1.45mg·g-1respectively; Chlorophyll a, b and a+b contents become lower as the increase of the RIB ratio. Also in64μmol·m-2·s-1PPFD LED light environment, the average main root length (RL) of Arabidopsis under the environment of LED light is20mm longer than that under fluorescent lamps. The number of lateral root is higher in LED light environment too. Under LED lighting environment, when the total PPFD changes from14μmol·m-2·s-1to375μmol·m-2·s-1, the main root length becomes longer, and then decrease when PPFD is higher than200μmol·m-2·s-1.Based on the absorption spectrum of the chlorophyll a and b, the concept of Photosynthetically Active Radiative Flux (ψa、ψb) was introduced to calculate how much radiative power are contributing to the chlorophyll a and b. Differences between LED light sources and differences between ψa、ψb and photometry parameter luminous flux are discussed. The concept of Photosynthetically Active Radiative Flux can be used in the agriculture light source and control system design, and its derivation method can used as a reference method for new plant optical performance indicators.