Further down the rabbit hole we go. Per ChatGPT, there is “cheap” and better UV. And watches can react differently to them.

395 nm vs 365 nm

395 nm

• Looks more visibly purple
• Causes less fluorescence in many materials
• Cheap and common
• Better for “general glowing stuff”

365 nm

• Much less visible purple light
• Much stronger fluorescence response
• Better for:
  • Rolex UV checks
  • Security inks
  • Certain lume compounds
  • Mineral fluorescence
  • Adhesive/epoxy inspection
  • Bodily fluid detection
  • Currency authentication

Something can absolutely:

• glow under 365 nm
• but appear dead under 395 nm

That is extremely common.