The prop was not custom-made in the Star Trek Art Department, but it is available from a company called Modern Props. It was originally built for the original Incredible Hulk TV series, according to Modern Props founder John Zabrucky. The prop is described as "dual generators with rotating neon lights inside an acrylic tube; light-controlled panel with knobs and buttons." The tubes appear in other science fiction series and movies as well, such as "Airplane II" (with William Shatner), "V" (the 1983 miniseries), "The Last Starfighter" (1984) or "Austin Powers: The Spy Who Shagged Me".
Though the website for Modern Props is apparently defunct, Ex-Astris-Scientia did share the rental company's image of the prop from their catalog (above), along with numerous screen shots of it's appearance in TV and movies.