Method and apparatus for evaluating one or more materials in accordance with size of particles. The method includes evaluating a spectrum of light reflected from a first group of particles; evaluating a spectrum of light reflected from a second group of particle; comparing results of said evaluating of said first group with results of said evaluating of said second group; and providing an indication of a state of said material when said comparing produces a predetermined comparison result. Distance between a first light conductor for conducting light to the particles and a second light conductor for conducting light from said particles for said evaluations may be varied. Monitoring of a process for changes in particle size as a function of time or to determine various physical and/or chemical characteristics of the particles or a mixture containing same, including homogeneity, may be achieved.