Back about 1974/5 I bought a Model 70 375 H&H and did some hunting trips on Afognak Island (near Kodiak Island), Deer, Elk and of course there are some rather large bears.
As we know bears travel and night and I wanted something to use at night. I found a Weaver K 2.5 and put that on my Model 70. If you had any moon at all, it was almost like daylight.
Great scope for low light conditions.
Later I guess during a period when Weaver went under (if it really did) I couldn't kind a similar scope for my Model 70 Featherweight in 257 Rbts. I ended up with a Leopold Compact 2.5 scope. It was good in low light but not as good as my K 2.5 Weaver. Still a great scope.
When Weaver started putting out scopes again I couldn't find a K 2.5 for my FN Model 70 Featherweight in 270 so I went with the K-4, again a great scope, better then the Leopold Compact, almost as good as the K 2.5.
From all the scopes I've seen, the Weavers seem to be the best in light gathering abilities. I know many people on this form don't like Weavers, guess if they don't cost over a grand they aren't worth having.
I also got a Weaver 3-10 Mil/Mil scope, its a great scope, but to be honest I haven't used it much in low light conditions to voice an opinion.
I think if I was going to buy a scope for low light conditions, I'd go to the big sporting good stores like Cabala's Scheels, etc. after the sun goes down and tell the clerk you want to see how they work in low light, take them outside with the clerk and see. I've done that with spotting scopes and never had a clerk tell me no. They've been rather supportive.