I think what you are refering to is just the pattern present in the reflective tape. see post# 347Wonderful. but how are you getting it to glow thru carbonfiber??
This could also be the result of duplicate sabres 'going missing' at wind up of production of the films. From what I understand production crew, actors etc. have a habit of 'retaining' props as souvenirs. Not to mention the amount of stuff that looks to have ended up in a skip from ANH. Same thing could still apply to ESB? Reusing what they do have is just sensible cost saving.(reusing old stunt sabers means they didn't have a lot of duplicates)