The easiest way Ive compared scopes is side by side at the range close to dark. I dont mean after legal hunting time but in the last half hour of low light.

If you take a cheap scope like a Tasco or BSA and crank them up at low light looking out 150 yards or so its hard to see the target very clear. If at the same time I look through a high end scope like a B & L or Nikon(thats high end to me, I don't spend over 500$ fora scope) its very obvious how much clearer they are.

I hunt a large field a lot in the eveand at 250ish yards when its getting close to quiting time(when the bucks come out)I like to crank the scope up to max power and just can't do that and stillsee veryclear with the cheaper scopes. I have a couple of cheaper Simmons 3x9's that you cant turn up more then 4 or 5 power without it being just to dark that far out in the field.

Try to get a side by side comparison(not in the store)that how I can tell the biggest difference between the scopes. I know when we are out shooting some groups I can still shoot with my 4200's and see the targets fine while my buddy is putting away his guns with some of the cheaper stuff. I used to be a big believer in Leupold stuff and had a couple of VX III's and II's and after looking thru them at the range close to dark compared to my buds Monarchs and the B & L 4000 I have I sold all ofLuppys but 1 and happily wear Bushnellson most of my rifles. I have no doubt which are brighter.