Luminous material

The modern material is a ceramic pigment that stores light and gives it back. RC Tritec of Teufen, Switzerland, states in its own history that in the early 1990s Albert Reinhard Zeller "developed a ceramic afterglow pigment based on strontium aluminate doped with rare earth elements", and that this became Swiss Super-LumiNova®. The same history sets that against what the firm used before: Radium Chemie AG was founded in 1934 and made radium-based luminous paint thereafter, the page giving no start year for it, and then turned to tritium, since "In 1961, Radium Chemie AG was the first manufacturer to be granted an import licence for the American watch market with the new phosphor technology activated by tritium." Super-LumiNova is a named company's trademarked product, and these are that company's statements about it.

Swiss horological standardisation covers the coating. The list of available NIHS standards published by FH includes NIHS 97-21, Instruments de mesure du temps – Dépôts photoluminescents – Méthodes d'essais et exigences, test methods and requirements for photoluminescent deposits on timekeeping instruments. The list gives its title only, so none of its requirements is quoted here.

The nearest thing to an international requirement is indirect. ISO 6425:2018, Horology — Divers' watches, edition 4, published October 2018, applies to watches that include "a secured measuring system to indicate the diving time, which is visible in darkness". That makes readability in the dark a condition of the divers' watch standard without naming the material that achieves it. Only the standard's published scope has been read; the text is paywalled.

Radioactive luminous materials are a separate, licensed category. Under United States regulation, 10 CFR 30.15 exempts from licensing timepieces containing not more than "25 millicuries of tritium per timepiece", "5 millicuries of tritium per hand" and "15 millicuries of tritium per dial (bezels when used shall be considered as part of the dial)", with much lower limits for promethium-147. A pigment charged by light is subject to no such limit.