We used incidence-radiation relations to elucidate scintillation^<2)>. Since these equations may be used also in computer graphic etc., they are presented in this paper. In the equations, i (angle between optical axis and incident ray) is derived from four cases (table→table, main→table, table→main, main→main), and an optical path follows on θ(angle between optical axis and radiant ray). These symbols have suffixes c and cc representing clockwise and counter clockwise optical paths, respectively. In the case that these rays are inclined to right-hand path against optical axis, these symbols should be indicated by negative sign. Final, graphical check is useful, since there can be imaginary cases, if deseision in made simply on calculation.