Cinefex 1983 says
During principal photography, actors Mark Hamill and David Prowse used mockup swords with solid shafts — or, in some cases, wielded only the hilt. In postproduction.. Visual Concept Engineering — under supervision of ILM alumnus Peter Kuran — painstakingly rotoscoped each frame and produced the glowing shafts which characterize the traditional Jedi sidearm.
The Wikipedia claim is based upon the 1994 article British Olympic fencer Bob Anderson trains actors for ''The Three Musketeers'' which says:
”That’s not very well known,” Anderson says. Vader actor David Prowse explains that he did his own swordplay in Star Wars, but when the movie became a hit deserving of sequels, ”having one of the principals do his own stunts made (the filmmakers) very weird from an insurance point of view.”