I used to hunt deer a lot with a .54 Leman half stock round ball rifle I built in the '80s. I mounted a Swiss style peep sight on the wrist for target work. When I hunted deer I would leave the disc in place on the rear sight, with it's tiny aperture, but when dusk came I would unscrew the disc and use the threaded female base as a ghost ring. With a good post (blade) front, I could shoot it very well. Actually, not much larger groups than with the disc in place.
Peeps and ghost rings are capable of very fine work. Low light is no issue with a ghost ring. They are the cat's meow for aged eyes, as you basically ignore the rear sight and let your brain center the front sight in it automatically, focusing only on the front. No effort involved.
NECG makes a nice ghost ring rear sight.
http://www.newenglandcustomgun.com/gun_services/Peep_Sights.asp SRH