follow up from responses in old thread. https://www.physicsforums.com/threa...icient-decrease-with-increased-energy.569981/ I have seen in my experiment using a saline media ( some oxygen bubbles) that an increase in Incident PFD is showing an slight increase in the attenuation coefficient. In theory I should be getting the same coefficient. Can an increased number of photons cause increasing number of photon collisions? My data is reporting a linear increase in attenuation coefficient at increased incident PFD.