Paul,

The list of scope brightness test results is in a chapter of my book MODERN HUNTING OPTICS, published in 2014. There have been a few more tests since then, including the Tract Toric, but otherwise the list's pretty complete, and the chapter explains both the test methodology and the stuff that can affect image brightness.

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck