Hiviz sight for Ruger Mark II pistolHi-Viz gun sights improve a shooter's ability to get on target and see his sight picture clearly, even on low light days. The fluorescent light pipes gather ambient light, giving you the amount of light transmission you need for a given light condition - never too bright or too dim! Light pipes are usually available in one or both of two colors:  FLUORESCENT GREEN or FLUORESCENT RED. Some of the popular models are shown here:

Hiviz sight for Ruger 10/22
Hiviz sight for Glock
Hiviz shotgun front bead sight
Hiviz sight for vent rib shotgun
Ruger Mark I/II/III (bull barrel only), Browning Buckmark, Ruger Single Six
Ruger 10/22
Glock sight available as front and rear sights
Replacement front bead for most shotguns
Magnetic, snap on front sight for most vent rib shotguns

Other models are available for Colt and MILSPEC AR15/M16/M4, Walther P22, Springfield Armory XD, Ruger Redhawk/Blackhawk Hunter, Browning High Power, Smith & Wesson M&P pistol, Ruger GP100, Ruger P89/90/91/94, Smith & Wesson revolver, CZ75/85/97/83/P01, and Colt M1911A1
The next best thing to tritium sights, Hiviz sights will not glow-in-the-dark. They rely on Lite Pipes, similar to fiber optics, and do an excellent job of turning available light into bright, fluorescent dots for eyes to use. You'll love your Hi-Viz sights! They are quality made in the United States by North Pass Industries.
Use caution! Oil, grease, solvent, or any petroleum based product will destroy the light pipes. Clean your firearms carefully and cover the Hi-Viz sights during cleaning.