bright idea

A clever thought or plan. For example, John had a bright idea for saving space—we would each have a terminal but share the printer. This term uses bright in the sense of “intelligent” or “quick-witted” and may be employed either straightforwardly, as in the example above, or ironically, as in Jumping in the pool with your clothes on—that was some bright idea. [Late 1800s]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.