They make a replacement set of sights that are plastic rods that glow. Hi Viz makes them and maybe others. http://www.hivizsights.com/ruger.htm You can also put on a peep rear sight. Most people like the smaller hole of the two. http://www.oneraggedhole.com
www.rimfirecentral.com has had alot of discussion about this stuff reciently. Check the Ruger-Other room.