A method of making a light converting optical system comprising providing a first optical layer, a thin sheet of reflective light scattering material, a light source, a second optical layer approximately coextensive with the first optical layer, a continuous broad-area photoabsorptive film layer approximately coextensive with the first optical layer, positioning the thin sheet of reflective light scattering material parallel to the first optical layer, positioning the continuous broad-area photoabsorptive film layer between and parallel to the first optical layer and the thin sheet of reflective material, and positioning the second optical layer on a light path between the light source and the continuous broad-area photoabsorptive film layer. The first optical layer has a microstructured broad-area front surface comprising an array of linear grooves disposed side by side and extending along a straight line between two edges of the layer.