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.