/ Dictionary / Index L light pipe: Meaning and Definition of Find definitions for: light' pipe" Pronunciation: [key] — Optics. Optics. an elongated transparent medium, such as an optical fiber, for transmitting light. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. light pen lightplane Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language