Hello, I have a number of forge weapons that I never bothered adding Obsidian Radiance to. I currently have 3 in my inventory. When trying to apply one of my Obsidian Radiance mod to a weapon i.e. Kindled Orchid, it does not appear. Pictures attached show both having them in my inventory, and not appearing when hovering over Base Radiance. Best of luck resolving the issues! https://imgur.com/ddHbkWw https://imgur.com/D0aYDew
The ones in your inventory are Obsidian Accelerators. Take those to Ada to create the Radiance Mods. Look on the second page of her inventory (been awhile so this is from memory).