Illumination device with light diffusion plate

An illumination device comprising:

• a substrate having a convex surface;
• a plurality of solid-state light sources secured on the convex surface, the plurality of solid-state light sources defining a central axis;
• a light diffusion plate arranged generally adjacent to the convex surface of the substrate, the plate comprising a concave incident surface and a convex output surface, the concave incident surface facing the convex surface of the substrate for receiving light from the solid-state light sources, and the convex output surface being for emission of the light to the outside of the illumination device, at least one of the concave incident surface and the convex output surface having a plurality of parallel micro-structures each having a length parallel to a first reference axis, the micro-structures being arranged in two groups at opposite sides of the central axis, the micro-structures of the two groups being symmetrical relative to each other across the central axis, and the micro-structures configured for increasing a radiating range of the light entering the plate, the increase of one of the groups of micro-structures being along one direction of a second reference axis, the increase of the other group of micro-structures being along an opposite direction of the second reference axis, the second reference axis being substantially perpendicular to the first reference axis.