Light to light efficiencies in Luminescent Solar Concentrators

Luminescent Solar Concentrators (LSC's) were thoroughly explored over a decade ago for use with photovoltaic cells. However LSC's as a source for lighting have received less attention than is deserved. To evaluate the lumens supplied by a LSC lighting source over the course of a year and in a fixed orientation it is necessary to know the light-to-light conversion efficiency. We present a model for this and examine its sensitivity to the geometry of the LSC and light transport losses for light guided within the Lsc. The latter depends on dye concentration due to spectral overlaps of the absorption and emission bands and to bulk and surface losses due to defects. As a result of these effects the spectral distribution of the emitted light, and hence the colour rendering properties, depend on the size of the Lsc. Calculated spectra are compared with those measured in the laboratory for full scale Lsc's. Results for calculated efficiency as a function of length and dye concentration are given. It is found that properly orientated compact Lsc's can provide enough lumens under moderate external illuminance to illuminate a typical room in a house.