Universal optimal transmission of light through disordered materials
  We experimentally demonstrate increased transmission of light through strongly scattering materials. Wavefront shaping is used to selectively couple light to the open transport channels in the material, resulting in an increase of up to 44% in the total transmission. The results for each of several hundreds of experimental runs are in excellent quantitative agreement with random matrix theory. Extrapolating our measurements to the limit of perfect wavefront shaping, we find a universal transmission of 2/3, regardless of the thickness of the sample. 
I. M. Vellekoop and A. P. Mosk