An illuminated rifle scope is a telescopic or reflex rifle scope that incorporates a source of light, usually battery powered, in the scope’s construction. The light illuminates the reticule, or cross-hairs, enhancing the shooter’s targeting ability. It's important to note that the target itself is not illuminated; what’s lit up is the reticule so that it stands out better against the target under conditions of low visibility.
Rifle scopes, both telescopic and reflex, enhance a shooter’s ability to discern the target and aim the weapon properly, but when visibility is reduced, whether due to natural darkness, fog, or combat conditions, it’s difficult to aim a weapon properly because the target itself is hard to see. An illuminated rifle scope won’t be of much use when smoke or fog is obscuring vision, but it can help remarkably when visibility is reduced due to darkness.
Illuminated rifle scopes generally produce their illumination in one of three ways. The first is a simple battery-powered light bulb, usually a light-emitting diode (LED). The light source is located behind the reticule and aimed forward, illuminating the rear edges of the reticule, which are those facing the shooter. Rifle scope illumination is usually colored red, a color that will least disrupt the shooter’s night vision. An important consideration for an electric-powered illuminated rifle scope is the useful life of the power source, although recent developments in the field have resulted in guarantees by manufacturers that batteries will last more than 10 years.
Some manufacturers, especially for hunting-grade and military scopes, use radiological isotopes such as tritium as the source of illumination. These isotopes deteriorate over time, losing their brightness, and must also be replaced after 10 to 12 years or so. A third method of rifle scope illumination is the use of fiber-optic technology that collects the ambient light and directs it onto the reticule. Any illuminated rifle scope should be adjustable, because too bright a light illuminating the reticule can impair a shooter’s night vision.
Illuminated rifle scopes are useful both in military and law enforcement situations, where users cannot dictate the time of day they’ll be used. Hunters who find themselves in low visibility environments around dawn and dusk also value illuminated rifle scopes. A hunter with an illuminated rifle scope should check the local laws and regulations before using it, though, because some jurisdictions prohibit the use of illuminated scopes by hunters, or limit their use to situations of limited daylight only.