Microalgae and cyanobacteria are photosynthetic microorganism used as human nutrients. Light is the most important factor affecting the biomass accumulation and production of bioactive compound by photosynthetic microorganisms. However, excessive light can suppress their growth by damaging the photosynthetic machinery such as Photosystem II (PS2). Therefore, an LED-based illumination system that is used for cultivation of photosynthetic cells needs a device to appropriately regulate the light level, but the addition of an electronic dimmer increases the initial costs. Spirulina is one of the promising and representative photosynthetic microorganisms. In the present study, we describe the use of a new semicylindrical column photobioreactor for cultivation of Spirulina. The amount of incident light reaching the photobioreactor was easily adjusted by changing angle of the LED in relation to the flat surface of the bioreactor. Arrangement of the LED bar at a 45° angle led to the highest growth and chlorophyll content, and led to no retardation of cell growth during the initial growth phase.

Abstract
Introduction
Materials and Methods
    1. The setup of semi-cylinder photobioreactor andlight intensity control
    2. Cultivation of Spirulina platensis
    3. Dry cell weight and Optical cell density
    4. Measurement of chlorophyll content
Results and Discussion
    1. Comparing light efficiency according to surfacetype of photobioreactor
    2. A simple control of light intensity by changing theangle of LED bar toward flat-panel
    3. Validation of photosynthetic growth and chlorophyllformation in hybrid photobioreactor with new lightcontrol
References

• Chang-Su Lee(Division of Applied Life Sciences (BK21 plus), Gyeongsang National University)
• Do-Wook Woo(Division of Applied Life Sciences (BK21 plus), Gyeongsang National University/Department of Food Science & Technology and Institute of Agriculture & Life Science, Gyeongsang National University)
• Gyeong-In Lee(Division of Applied Life Sciences (BK21 plus), Gyeongsang National University/Department of Food Science & Technology and Institute of Agriculture & Life Science, Gyeongsang National University)
• Jong-Hee Kwon(Division of Applied Life Sciences (BK21 plus), Gyeongsang National University/Department of Food Science & Technology and Institute of Agriculture & Life Science, Gyeongsang National University) Corresponding author