In this paper a floating body partially depleted SOI MOSFET used to measure light intensity using the transient charge pumping [1] is modeled through an equivalent electrical circuit. Essentially, photogenerated charges of the MOSFET are converted into a charge pumping frequency needed to maintain the drain current constant during the illumination. This contrasts with other conventional methods that rely on an accurate quantification of the drain current to measure the light intensity. Flux densities as low as 2mW/m2 were measured, thus confirming the potential of this approach. © 2007 IEEE.