Reticle illumination is getting more common in modern rifle scopes. There are, however, two groups of illuminated reticles, meant for two different uses. In both cases, illumination of the reticle substantially increases effectiveness of such rifle scopes. Reticle illumination systems are divided to:
Twilight illumination is used for better reticle recognition in low light situations, when non-illuminated reticle would be hard to see. Such illumination systems must offer fine adjustable intensity, since over illumination of the reticle will cause problems seeing the target behind it. This is especially important when hunting in low light, where fine-tuning of illumination intensity level is one of the main parameters on which rifle scopes are judged. Preferably, such rifle scopes have only the central dot in the reticle illuminated. Some have their entire range of intensity adjustment so dim that illumination cannot be seen during the daytime.
Daytime illumination of reticle serves a different purpose than twilight illumination, and in such rifle scopes, high intensity levels are a necessity. In such rifle scopes, the illumination of the reticle is meant for rapid target acquisition, since a bright red dot is the best possible aiming point. Shooters’ eyes are instinctively drawn to a bright red dot in the center of the field of view. Such strong illumination is feasible only in rifle scopes with magnification lower than 1.5x or ideally 1.0x. Such wide-angle rifle scopes with a real 1.0x magnification and daytime bright illumination of the reticle can even be used with both eyes open, similar to reflex/red dot sights.
Since almost all illuminated reticles are battery powered, an automatic switch off is a usable feature that can significantly prolong battery life and operation time of such systems. Most advance reticle illumination systems even include a motion sensor that turns off the illumination (and saves battery life), when the scope is in non-shooting position (90 degrees sideways or in vertical position).