Constraints on the Optical-IR extragalactic background from gamma-ray   absorption studies
  Very high energy (VHE) gamma-rays from extragalactic sources, interacting by gamma-gamma collisions with diffuse intergalactic radiation fields, provide an alternative way to constrain the diffuse background light, completely independent of direct measurements. The limits depend however on our knowledge of the physics of the gamma-ray sources. After clarifying the interplay between background light and VHE spectra, I summarize the extent and validity of the obtainable limits, and where future improvements can be expected. 
Luigi Costamante
astro-ph.HE astro-ph.CO