Light emitted from a plurality of LED light sources can be introduced into a light guide and inwardly reflected at a first reflective surface formed on the light guide to form a substantially collimated light. The process can be used too for upgrading technical monoglycerides which contain free fatty acids. For this, the present invention includes an optical system for generating the parallel light within the solid immersion lens, and a unit for measuring the slant angle of the solid immersion lens using a location detection unit.