The aim of this work is setting up the conditions of an “iso-actinic” photobioreactor that is a photoreactor for the cultivation of microalgae in which the local volumetric rate of photon absorption (LVRPA), can be considered uniform to a good extent. We describe the composition of this cheap photoreactor and how we made it. The system is driven by an Arduino platform that makes it possible to control light intensity as well as light-dark cycles. Preliminary results obtained by growing Nannochloropsis gaditana, a microalga famous for its fat content, in this innovative reactor are presented. We finally observed how microalgae responds to flashing light irradiation.