A solution for fabricating a light diffusing sheet-like device capable of emitting light with superior brightness, that is a high brightness diffuser. The high brightness diffuser mainly includes at least two light diffusing pieces with ridge-shape structure arranged thereon, which can be either convex or concave. The convex ridge-shape structure having a plurality of large convex ridges and a plurality of small convex ridges, which are associated with a ridgeline existing in between two adjacent ridges where the large ridge and small are interlace-arranged, and the ridges along with the associated ridgelines can be longitudinally extended to the same direction. The concave ridge-shape structure is constituted the same way as the convex ridge-shape structure is, but having concave ridges. The high brightness diffuser is fabricated by stacking up the two light diffusing pieces and enabling an included angle to be formed between the two ridge-extending directions of the two light diffusing pieces.