Big Dot and Standard Dot Night Sights are defensive tritium sights designed to enhance your defense gun. The sights use a proprietary photoluminescent Glow Dot that absorbs ambient light and glows in low light. The convex dot’s additional surface area increases light absorption, intensifying the charge of the Glow Dot. Designed to be large and highly visible, these sights help solve many issues, from aging eyes to deteriorating vision. We’ve found that the orange front tends to be most visible in daylight settings and that yellow glows brighter in low light, while green is an excellent option for low light and has a very bright glow intensity. XS Tritium Night sights are big, bright, and easy to see day or night! This front sight fits Ruger SP101 with fixed rear sight. Pin hole for front sight must be drilled for installation of sight. Front Sight Dot Width: 0.188″. Overall Sight Height: 0.205″.