Is it legal to make a film with lightsabers in it in a different universe than Star Wars? Is it legal to make a sci-fi films where there are no Jedi, but people wield lightsabers that are very similar to the ones in Star Wars? Assume for the sake of the question that every character in the film is blue-skinned and they wield orange-colored lightsabers and it's set in a sci-fi universe completely different from that of Star Wars. Is this considered a derivative work and thus infringes copyright, or can it be considered to be an original just because the setting is different?
"Lightsaber" is a trademarked term, so it's gotta be called something else. The idea behind a lightsaber is older than Star Wars, anyhow idea are not protected by copyright. The actual design of such a weapon would be protected, but it would be a matter for the jury to decide if the supposedly-infringing design was a copy of a Lucasfilms-protected object, or that of the cover of Analog, Jan. 1969. The "setting" of the movie is completely irrelevant, all that counts is whether the object "copies" the plaintiff's design. In light of the earlier Wolfling design, it's not a foregone conclusion that all lightsaber-resembling objects are infringing. Available evidence indicates that you will be sued if you do it, so consult a really good IP attorney.