Quantity and Quality of Light on Growth and Pigment Content of <i>Dunaliella</i> sp. and <i>Anabaena</i> sp. Cultures and the Use of Their Absorption Spectra as a Proxy Method for Assessment

(1) Background: As microalgae cultures are affected by the quantity and quality of light, I explored this for two species. Additionally, I introduced a novel easy and economical way for the growers to easily and economically ascertain continuously with satisfactory accuracy the quantitative and qualitative status of their culture using absorption spectra. (2) Methods: The locally isolated chlorophyte <i>Dunaliella</i> sp. and the cyanobacterium <i>Anabaena</i> sp. were cultured in small volumes with two intensities of white light (2000 and 8000 lux) and with green, blue and red light, and the increase in their biomass and pigments was studied. Pigment analyses, continuous recordings of absorption spectra and calibration curves were used. (3) Results: The intensity of 8000 lux of white light yielded the highest increase in biomass, chlorophylls and carotenoids in <i>Dunaliella</i> sp., and the same was found for green and blue light, while 2000 lux and green light caused the greatest increase in biomass and phycocyanin in <i>Anabaena</i> sp. From the absorption spectra, the evolution of the pigment content can be estimated, and both pigments and biomass are correlated very strongly with those extracted from the spectra absorption of 750 nm. (4) Conclusions: The use of absorption spectra as an easy, fast and economical method can be a useful tool for a good approximation of the state of the microalgae culture. This is clearly shown when the spectra of the cultures under different light intensities and colors are compared having a catalytic effect on the level of the pigments leading to the increase in carotenoids and phycocyanin of the green light.