A light converting optical system employing a planar light trapping optical structure. The light trapping optical structure includes a monochromatic light source, a light guiding layer, a lenticular lens array incorporating a plurality of linear cylindrical microlenses, a broad-area reflective surface, and a generally planar photoresponsive layer located between the lens array and the reflective surface. The photoresponsive layer is configured at a sufficiently low thickness to transmit at least a portion of incident light without absorption in a single pass. A portion of the unabsorbed light is trapped within the light trapping optical structure and redirected back to the photoresponsive layer.