An inorganic thin film luminescent solar concentrator (LSC) is characterized experimentally in detail in terms of all the separate light transport steps, which result in the concentration of sunlight. The results are discussed in the context of application as windows in buildings, called building integrated (BI) LSCs. A 3 pm thin film of Eu3+ doped Lu2O3 was chosen because of its large Stokes shift, which excludes all waveguide losses due to self-absorption and allowed to study losses caused by scattering at interfaces of the LSC. A model is presented that can be used to calculate the LSC light transport efficiency as a function of window size, which only needs the easily measurable linear attenuation as input. Measurements show that the quantum efficiency (eta(QE)) of our LSC is 13%, which is less than ideal, mainly due to a 44% luminescence quantum efficiency and a 45% waveguide efficiency. Our modelling relates BI-LSC efficiency to window color, and reveals that the linear attenuation coefficient of an LSC should be higher than 1000 mm. This is in contrast to values in the order of tens of millimeters which have been measured for the LSC in this paper. (C) 2012 Elsevier B.V. All rights reserved.