The display inconsistency caused by light setting

My project is showing objects which have top,bottom,and side(like geological body). when the lights are set up, the top and bottom shapes can be viewed better,but the side (vertical) view of the object is too shinning,and not like the top or bottom view. I think there must be something wrong with the lighting setup. changing the parameters can not achieve the satisfied effect. I wonder if there is specific laws for setting the light, or how to achieve a better effect when facing this problem.^_^.thanks a lot!!