Numerical solutions for SCL currents in inhomogeneous insulators with non-uniform trap distributions are presented. It turns out that the non-uniform trap distribution which may be expected in the case of real insulators should have a significant influence on SCL current - voltage characteristics. The experimental results for some organic molecular polycrystalline structures may be interpreted by using the numerical solutions obtained. A method of determination of the spatial trap distribution at the emitter by means of photo-enhanced SCL currents is also presented.