Here is what is arguably the most important device in the universe: a pair of blinking tubes with absolutely no functions whatsoever that appeared in countless sci-fi movies and tv shows! It is the ultimate re-used prop, and in all the cases where it appeared on screen, there was not a single occurrence where its purpose would be explained.
The first time we see it is in the Regula lab in “Star Trek II Wrath of Khan”. They are also visible in the Enterprise-A’s shuttlebay in “Star Trek V”
They also appear in a number of Star Trek Episodes:
TNG: “Suddenly Human”
TNG: “The Quality of Life”
VOY: “Inside Man”
Finally the prop can be seen in Soong’s hideout as well as on the research station in ENT: “Cold Station 12”.
It appears in the background of various science labs in “Lower Decks” , in cartoon form.
The tubes appear in other science fiction series and movies as well, such as:
“V” (the 1983 miniseries),
“The Last Starfighter”.
“The Incredible Hulk Returns” (1988 TV movie),
“The Flash: The deadly Nightshade” (1990) ,
“Star Crystal” 1986
“Alien Nation”, as well as “Airplane II” (with William Shatner, who would again encounter it in Star Trek V: The Final Frontier which he directed and starred in.
It also appeared in “Lois & Clark” episode 2×08 with Denis Crosby.