   two side lighting
  I sorry for the confusion I open this new post for explain what i wish do:I have a shader that displays a front/back material color face and i would create a light system like the sun that illuminates both the front and the back face of a mesh(for example a quad) in all camera position.i think that i must use a directional light but if i use two directional lights with opposite direction for lighting the two side of the mesh the diffuse component is 0 .How i can illuminate the two side of the quad?thanks   