Luminescence is a watch term used to describe the glow emitted from the hands and markers on the watch face. This glow is achieved through the use of a special material that emits light, such as a phosphorescent or radioactive material, when exposed to a specific type of energy, such as UV light. This light, which is emitted from the watch face, makes it easier to tell the time in dark conditions, making it a very useful feature for a watch.