Study Of Effects Of LED On Promoting Growth Of Microalgae

People have set off an upsurge in the utilization of marine resources because of the sharp consumption of terrestrial resources. Some kinds of Microalgae have become important targets in aquaculture for their rich biological nutrients. Since light has a significant impact on the growth of algae and accumulation of various bioactive substances, the research on the effect of light on microalgae cultivation has been an important subject in aquaculture.Light Emitting Diode (LED), as a new type of solid light source, is considered to be fourth-generation light source after incandescent lamp, fluorescent lamp and high-pressure discharge lamp. Now various kinds of LED have been used in illumination and display fields, and it's natural and necessary to extend its application into the field of ecology. This thesis has studied the effect of light quality on the growth of four kinds of microalgae by using monochromatic LED, discussed some fundamental questions in ecology-lighting, such as the quantitative characterization of light quality and the efficiency of light on promoting growth, and attempted to design LED light sources for ecology-lighting, so lays a foundation for the application of LED in ecology-lighting.There are three kinds of measurement of light intensity, which are luminosity measurement, radiant measurement and quantum measurement. Due to historical reasons, there is some misusage of the three in ecology-lighting. This thesis analyzes the mechanism of the three, and explains that quantum measurement should be the appropriate one for ecology-lighting. Based on the relation of the three in energy, the conversion coefficients among the three can be calculated by using relative power density spectra of light, which make experimental results in different kinds of measurement universal, and expand the function of instruments for light intensity measuring.In ecology-lighting, light quality didn't draw enough attention as light intensity and light periodicity in past research, and was described in qualitative way, such as blue light or red light. Focusing on speed and efficiency, effects of five different spectra on the growth of four kinds of microalgae are investigated by using monochromatic LED and fluorescent lamp. It is concluded that the efficiency of light in ecology-lighting is according to its spectra, i.e. light quality, and light with continuous spectra promote higher top-growth-rate than that with zonal spectra. Based on the analysis of photosynthesis reaction mechanism, the concept of absorption coefficient to spectra of light is tentatively advanced by considering the relation between the spectra of light and absorption spectra of microalgae. Since it can be used to explain the experimental laws at a certain extent, it is logical to use the concept to characterize light quality quantitatively. After that, LED of 8 different peak wavelengths are chosen to obtain special kind of light by adjusting their relative light intensity, which has continuous spectra and high absorption coefficient to spectra, and thus is expected to promote high growth rate of microalgae. And this work lays a foundation for the practical application of LED in microalgae cultivation.Furthermore, on the base of appropriate measurement of light intensity and quantitative characterization of light quality, the formula for calculating photosynthetic efficiency of light source from its luminescence efficiency is provided to primarily quantify the efficiency of light sources in ecology-lighting.