This Letter introduces an analytical approach to estimate the waveguiding efficiency of large-area luminescent solar concentrators (LSCs), where the edges are covered by a var-ied number of mirrors and solar cells. The model provides physically relevant description in the whole range of optical (absorption, scattering) and geometrical (size) parameters of rectangular LSCs. A 19 x 19 cm2 silicon quantum dot -based LSC has been fabricated to verify the theory. Within an experimental error, the predicted waveguiding efficiency matched well the measured one. A critical LSC size, beyond which a part of the device turns inactive, has been deter-mined as N/& alpha; for N attached solar cells (one or two) and LSC material absorption coefficient & alpha;. This model provides a straightforward waveguiding analysis tool for large-area LSCs with different structural parameters relevant for both high concentration ratio and glazing applications.