Under favorable circumstances, as in They thought he'd make a wonderful mayor, but they'd only seen him in a good light, or The book portrayed their actions in a good light. Both this expression and its antonym, in a bad light, transfer physical light in which something can (or cannot) be seen clearly to figurative use. The literal terms date from the early 1500s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.