Light emitting device with phosphor wavelength conversion

1. A light emitting device comprising:

a substantially planar light transmissive substrate having a light emitting surface and an opposite surface and wherein the substrate is configured as a light guiding medium;

at least one phosphor material disposed as a layer adjacent to 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,

wherein the source is configured to couple excitation radiation into the substrate such that it is waveguided within the substrate by total internal reflection;

wherein 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, and

wherein light of the first wavelength and light of the second wavelength are emitted through the plurality of window areas.

2. The light emitting device of claim 1 , wherein excitation radiation is coupled into at least a part of one edge of the substrate.

3. The light emitting device of claim 1 , wherein the layer of phosphor material comprises a pattern of regions and wherein the window areas are defined by the gaps between the phosphor material regions.

4. The light emitting device of claim 3 , wherein the phosphor material regions are selected from the group consisting of being: substantially square, substantially circular, substantially elliptical, substantially triangular, substantially rectangular, substantially polygonal and combinations thereof

5. The light emitting device of claim 1 , wherein the window areas are selected from the group consisting of being: substantially square, substantially circular, substantially elliptical, substantially triangular, substantially rectangular, substantially polygonal and combinations thereof.

6. The light emitting device of claim 1 , further including a reflecting layer positioned adjacent to at least a portion of the surface of the substrate opposite the light emitting surface.

7. The light emitting device of claim 1 , wherein the light emitting surface of the substrate further includes a surface topology configured to promote the emission of light from the light emitting surface.

8. The light emitting device of claim 1 , wherein the layer of phosphor material comprises a pattern of at least two different phosphor materials.

9. The light emitting device of claim 1 , wherein the second, longer wavelength photoluminescent light emitted by the phosphor layer is selected from the group consisting of green, yellow, orange, and red light.

10. The light emitting device of claim 1 , wherein the substrate is selected from the group consisting of an acrylic, a polycarbonate, a polythene and a glass.

11. The light emitting device of claim 1 , wherein the at least one excitation source comprises an array of blue light emitting LEDs.

12. The light emitting device of claim 1 , and further comprising at least one source of red light that is configured to couple red light into the substrate.

13. The light emitting device of claim 1 , wherein the at least one phosphor material is disposed as the layer on the light emitting surface.