Normalized chlorophyll fluorescence imaging: A method to determine irradiance and photosynthetically active radiation in phytoplankton cultures

Abstract In order to expand microalgae's use as a mainstream biotechnological resource, the efficiency of light capturing in culture vessels must be optimised. As a response to the complex nature of microalgal culture vessel modelling, it is important that a robust method to assess irradiance in photobioreactors (PBR's) is developed. Several hardware based or mathematical models to predict irradiance exist; however, these methods can be impractical as they are time-consuming, depend on growth vessel geometry or species to be cultivated. In this work, a chlorophyll a fluorescence imaging method was developed to assess both light penetration and utilisation in PBR's. This new method, termed normalized chlorophyll fluorescence imaging (NCFI), allows users to obtain images (light maps) that reflect irradiance as a function of depth into the PBR. This information is then combined with biophysical measurements to provide both 2D maps and 3D models of wavelength dependent light utilisation in PBR's. The methods presented in this work aim to demonstrate how these kinds of measurements are undertaken, the potential artefacts one may encounter and its utility for designing efficient PBR's that are optimised for maximal photosynthetic productivity.