The conversion of light energy in algal culture was quantitatively studied under various growth conditions. Absorbed light energy during growth and energy fixed in organic material were estimated. The efficiency of the conversion was expressed as percentage of fixed energy (calculated from estimates of dry weight and elemental analysis of the cell. Often almost complete light absorption was achieved by high cell density or thick culture layers.To estimate the maximum fixation of solar energy, such dense cultures were used under natural conditions. Large cultures had an efficiency of 1-5 % of the incident light energy in April-November (λ< 0,7μ) and a yield of 1-13 g per metre 2per day, and small dense cultures one of 8 % and a yield of 20 g per metre 2per day during July and August. From mathematical description of the relation between light intensity and the rate of photosynthesis, yields were calculated for dense cultures. The yields and efficiency of light energy conversion calculated in this way were confirmed in experiments under controlled conditions. The influence of temperature was studied. The source of nitrogen influenced the efficiency of the light conversion but not the chemical composition of the cell. Nitrogen deficiency decreased the efficiency and increased the relation carbohydrate/protein. High lipid contents were attained only after prolonged growth periods, and were associated with very low efficiencies.
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