Many kinds of photosynthetic bacteria and microalgae
produce unique bioactive materials, such as pigments, proteins,
fatty acids and vitamins. In cultivation of these photosynthetic
cells, the design of photobioreactors for effective
illumination is essential to reduce the production cost. While
sunlight is the cheapest light source available, its light intensity
fluctuates diurnally and seasonally, and its energy intensity
is limited. To attain controlled cultivation conditions
and productivity, electric illuminating devices that convert
energy to light with high efficiency and emit light with favorable
physiological effects on photosynthetic cells must
be used in photobioreactor systems. Light emitting diodes
(LEDs) have narrow light emission spectra, high conversion
efficiency and low heat emission. The physiological effects
of light with a specific range of wavelength on photosynthetic
cells have been widely studied by using combinations
of special light sources and filters. LEDs can be useful light
sources for this purpose, because a wide variety of LEDs
emitting from red to purple light are now available.