A light guide plate (20) includes a light input end (21), a light output face (23) adjacent the light input end, and a back face (22) opposite to the light output face. A plurality of fine dots (26) are formed on the back face arranged in a uniform, rectangular array. The dots in a same column have a same size. The dots in a same row increase in size. A radius r of the dots in each row thereof varies as a function of a column number X of a given dot, in accordance with the formula: r=A+BX+CX2+DX3+EX4+FX5, wherein: the column number X varies in consecutive whole numbers from a value of one for the column nearest the light input end to a maximum value for the column most distal from the light input end; and A, B, C, D, E, and F are constants.