Gradient computing suffers the noise and ill-definition problems such that local shading is not sufficient for medical imaging to get accurate visualization. However, the current global solutions are either time-consuming or limited to single light source that easily leads misinterpretation. This paper introduces a gradient-free approach to interactively approximate the effects of multiple lights for transparent volume data. Using attenuation maps, our lighting method gets rid of the tricky normal estimation and improves the spatial perception. In addition, the proposed method can be extended to explorative models, ex: plane cutting and modified maximum intensity projection (MPI), to get better inside view of medical applications.