Stumpy,
The ZRS is a top notch glass, but it is rather typical of 42mm class binoculars as far as low light performance goes. As you get past 30-40 minutes past sunset. depending on overall light conditions, they get less bright, but just about all 42mm glass does. The best 42 mm glass I have seen in low light is the Zeiss FL. Very high light transmission percentage coupled with a brighter, cooler color balance. The ZRS has a warmer, somewhat reddish color cast.
You may need to look at an 8x56 of some nature if low light performance is really critical. The ZRS is a typical sort of 42mm glass and that they do lots of things well, especially considering the price, but will not excell at low light. They are not bad there, but you will have to go bigger objective to improve much on what they will do.
Last edited by SteveC99; 09/28/12.