A Simple and Reliable Method to Determine Mean Incident Light Flux Densities on Cylindrical Photoreactors and Photobioreactors from a Unique Fluence Rate Measurement

A new method to determine the hemispherical incident light (photon) flux density onto cylindrical photoreactors or photobioreactors is presented. It applies to situations where the photo(bio)reactor is radially illuminated by surrounding artificial sources or solar light. It relies on the direct measurement of a fluence rate with a spherical sensor put at the center of the reactor. Theoretical relations leading to the calculation of the hemispherical incident light flux density from the fluence rate value are established, and a web application performing those calculations is made available. It relies on a view factor, the expression of which, established for the first time with any assumption of the angular distribution of light at the boundary, is given. This requires a proper definition of the degree of collimation for the incident radiation field. Two different and complementary experimental devices are used to validate the method. As a result, the proposed method appears to be simple and reliable; it even looks faster and more accurate than actinometry for this particular geometry.