Phosphor was a substance that produced visible light when exposed to radiation.
On Earth during the 1980s, diving wristwatches were manufactured with dials painted in phosphor. In 2022, Pelia gave one such watch to La'an Noonien-Singh to assist in her search for a cold fusion reactor in Toronto. By removing the watch's glass cover and exposing the dial to air, Noonien-Singh was able to use it to detect the tritium produced by the reactor. (SNW: "Tomorrow and Tomorrow and Tomorrow")