What is indicated by gradual blackening at the ends of component "4" shown in figures "B" and "C" of the illustration? Illustration EL-0081

Correct Answer: Option B — The tube is nearing the end of its useful life.

Gradual blackening at the filament ends of a fluorescent tube results from electron emission material boiling off the tungsten cathodes during normal operation, signifying the tube is reaching the end of its useful lifespan.