The material for lampshade is Translucent shader with Absorbtion node group color input from blenderdiplom.com mixed with Diffuse shader to tone it down a bit. The question is: Isn’t the front face supposed to be brighter (as light hits it directly) than the back one lighted after the light passes through it?
No, in general Tranclucent BSDF is black in that case, as it reflect zero light back to light direction. It depend on other tricks you use with mix and diffuse node tree.
Translucent only pass light in one half space separaded by surface direction, and never “reflect” light, think as as sort of frost transparent w/o reflection. It is opposite to diffusion in that regard.
