 This activation and subsequent light emission process can be repeated again and again, and the material does not suffer any practical aging.Strontium aluminate–based pigments have to be protected against contact with water or moisture, since this degrades the light emitting quality.Tritium-based devices called "gaseous tritium light source" (GTLS), that are an alternative for afterglow pigments, have the advantage of being self-powered and producing a consistent luminosity that does not fade during the night.