The most determining aspect of algae cultivation is presence of photosynthetically active light (400-700nm). It
can be used by algae for capturing CO2 during photosynthesis. The construction of photoreactor must provide even
light intensity in whole volume. The theoretical efficiency of light energy conversion into chemical energy in the
process of photosynthesis is 11% [2]. Under dark conditions algae use up the stored energy for respiration.
Depending on temperature and other conditions, up to 25% of biomass produced during the day may lost again
during the night [3]. Even if this loose might be considered as unnecessary from biomass production point of view,
for correct energy conversion, the cultivation conditions must take into account both phases of photosynthesis –
light and dark [4]. Studies conducted by Hobson et. al [5] demonstrated that the photoperiod directly regulates the
rate of division. When the light phase is short (6h) the level of chlorophyll in the cell increases, but biomass growth
is low, and there are also significant losses due to respiration taking place in the dark. On the other hand, when light
period is long- over 18h the amount of chlorophyll in the cell is low and biomass growth is also small due to the
possibility of occurrence of the process of photorespiration mentioned above, or inhibition of enzymes controlling
the absorption of CO2.