A light emitting device comprises a substantially planar light transmissive substrate having a light emitting surface and an opposite surface. The substrate is configured as a light guiding medium. The light emitting device also comprises at least one phosphor material disposed as a layer on the light emitting surface with a plurality of window areas and at least one source of excitation radiation of a first wavelength positioned adjacent to at least one peripheral edge of the substrate. The source is configured to couple excitation radiation into the substrate such that it is waveguided within the substrate by total internal reflection. Additionally, the light emitted by the device from the light emitting surface comprises first wavelength radiation and second, longer wavelength photoluminescent light emitted by the phosphor layer as a result of excitation by the source.