Super-LumiNova is not a generic "luminescent material": it's a photoluminescent compound based on strontium aluminate, produced by Swiss company RC Tritec under license from Japanese Nemoto & Co. It replaced radioactive tritium in the vast majority of watchmaking production starting in the Nineties, and today it is the de facto industry standard. It emits no radiation: it absorbs photons from natural or artificial light and releases them progressively in darkness as visible glow.
Commercial variants are distinguished by emission intensity and color. BGW9 is the historical formulation with green-blue emission, still widely used in divers. C1 indicates blue emission; X1 and X2 are successive generations with greater initial brightness and slower decay — X2 is what Panerai uses on sandwich dials PAM, where the luminescent paste is applied to the lower plate and becomes visible through the index cutouts. The code that follows (C1, C3, BGW9) describes the emission color: green, blue, green-white. Some manufacturers use multiple colors on the same dial — the Sarpaneva Moomin 80 declares ten, one for each painted dial element.
From my workbench I often see confusion between daytime color and nighttime color of the material. They don't necessarily coincide: the Sternglas Hamburg Pro Alabaster has mint green lume by day, but changes tone in emission. Bell & Ross's LUM-CAMO is black in full light and reveals photoluminescent properties only in darkness — it's a composite of carbon fiber with Super-LumiNova resin, not simple paint. These are things you can't read on the dial: you have to turn the light off.
Application changes the result as much as the formula. On normal dials the compound is painted on the indices or fills milled incisions. On sandwich dials — Panerai leading the way, but not alone — it's deposited on the lower layer: this protects luminescence from surface wear and gives that characteristic depth effect. The thickness of the deposit affects emission duration: a full C3 lume index holds an hour longer than an index with a thin layer. There is no official data shared by manufacturers on this point, so I trust what I measure myself in the lab with total darkness and a stopwatch.
Super-LumiNova decays: after ten to fifteen years of intensive use, performance reduces noticeably, especially on watches worn daily under poor fluorescent light. The material cannot be restored by lubricating or cleaning the crystal; it requires a new application. On a Nineties vintage I treat this as normal wear, not as a defect.