New Efficient Parameter and Respective Units for Measurement of Light Irradiation Availability in Microalgae Photobioreactors

Interest in microalgae cultivation is continuously growing due to their tremendous potential for a broad spectrum of applications. The established units for the measurement of a crucial parameter for algae growth, i.e., the light dosage in photobioreactors, are susceptible to severe criticism. Various units are currently utilized without however accounting for the volume of the culture exposed to light, which might differ depending on the reactor volume. Two new units of light irradiation measurement are proposed, namely, lxh (lux-hour) and lxhm×day. For the latter, lxhm×day, the parameters taken into account include the light illuminance, light exposure time, and volume and surface of the culture in the reactor, which are commonly measured. Cylindrical and flat-panel reactors are studied to determine the constant light illuminance and variant illuminance within a day period. It is shown that the unit lxhm×day is much more objective for expressing the light availability in photobioreactors than the current and most common expressions. The proposed parameter could be useful for comparisons of different experiments in a reactor or for up-scaling purposes.