A method includes having test plate and light source, the test plate having matrix of first pattern-dots and equally divided into blocks. Intersecting surfaces between the first pattern-dots and the first bottom surface have the same radius rx. Detecting a luminous flux ΦX of each block and a total luminous flux Φt of the test plate when light source is activated; calculating an average luminous flux Φave; calculating the radius rx1 of the first pattern-dots in each block assuming that an actual luminous flux of each block is equal to the average luminous flux according to the formula rx1=rx×sqrt (Φave/ΦX). Providing a substrate having the same structure as the base and the substrate being divided into blocks according to the same principle as the test plate. Forming second pattern-dots having the same arrangements as the first pattern-dots and having radius of rx1 in each block.
