Night LED illumination in the temperate regions as a model of polar day for algal cultivation in field-installed photobioreactors: Comparison of Svalbard and Central Europe

The low-temperature algal biotechnology starts to develop in the Polar Regions, and especially in the Arctic. Light is crucial environmental factor in algal mass cultivation, therefore knowledge of the light environment and its modeling is crucial for design of the photobioreactors. The light conditions in three different environments were compared: natural diel light cycle during the polar summer (June-August) in Svalbard and in winter/spring (January – March) in the Central Europe outdoor and in the greenhouse photobioreactor, and in greenhouse photobioreactor equipped by additional night LED illumination in central Europe in winter/spring. In Svalbard, the monthly mean diel PAR values ranger from 126 to 395 µmol m-2 s-1, and the monthly diel sums of the PAR ranged from 2.38 to 7.47 MJ m-2 d-1. In the Central Europe in natural diel light cycle, the monthly mean diel PAR values and monthly diel sums of the PAR were generally lower, 57 - 248 µmol m-2 s-1 and 1.08 and 4.69 MJ m-2 d-1 in outdoor and 26 – 107 µmol m-2 s-1 and 0.50 – 2.03 69 MJ m-2 d-1 in the sun-illuminated photobioreactor. When additional night LED illumination, lasting from 12 to 14.7 hrs and from 12 to 15.3 hrs in 2021 and 2022, respectively, was provided, the monthly mean diel PAR values and monthly diel sums of the PAR increased to 479 – 598 µmol m-2 s-1 and 9.06 – 11.31 MJ m-2 d-1, respectively. Since the Svalbard maxima of diel sum of PAR are comparable to the values found in the night LED illuminated greenhouse photobioreactor, the night LED illumination in winter/spring in Central Europe should be proposed for model cultivations in the Polar Region in summer.