Light map optimization via direct chlorophyll fluorescence imaging in algal photobioreactors

Microalgae are photosynthetic organisms that can be grown in photobioreactors (PBRs). The light placement within the PBR is crucial to optimize growth. Currently, the light path is often estimated from various mathematical models, which may result in less efficient placements of lights. Here we describe a novel fluorescence imaging technique to map the light within a bioreactor. These light maps describe the photosynthetic photon flux density (PPFR) inside the PBR, resulting in a precise light pattern of the LEDs and potential light reflections of the reactor walls. Furthermore, when compared with conventional imaging measurements that uses visible light, the fluorescence imaging technique has the advantage that only fluorescence emissions of microalgae are recorded. Regions of the PBR that show fluorescence emission can be assumed to have photosynthetic activity with sufficient irradiance of the specific photosynthetic active radiation (PAR) wavelengths. This method is adaptable to complex photobioreactor geometries and could be used to identify light-saturated areas. Two microalgae species and three colours of LEDs (red, blue, and white) were analysed in regards to light penetration and light distribution at different cell concentrations.