Photosynthesis makes use of solar energy to convert CO2 into glucose. This process is vital for life on Earth. Photosynthesis can only use parts of the solar spectrum that are in the photosynthetic active radiation range (PAR) (irradiance between 400 and 700 nm). Based on the measured average solar spectrum at the Earth’s surface, the proportion of total solar energy within PAR is about 48.7 % of the incident solar energy (Zhu et al. 2008). Pigments are responsible for capturing this light. Photo­synthetic organisms contain several pigments. As a matter of fact, pigments are responsible for the names of different divisions and classes of algae. For instance, Cyanophyceae and Rhodophycea contain Chl a and phycobillins, while Haptophy — ceae and Bacilariophycea contain Chl a and c. It is to be noted that all photosynthetic organisms contain Chl a which has the strongest absorption at 430 and 662 nm.

Other accessory pigments have different absorption spectra allowing the organism to more effectively collect different spectra of light (Frigaard et al. 1996). The absorption spectra of some microalgae species are summarized in Fig. 15.2.