You mean literally, sunlight is not a disinfectant? (false, https://www.cdc.gov/safewater/solardisinfection.html https://www.cdc.gov/safewater/solardisinfection

You mean literally, sunlight is not a disinfectant? (false, https://www.cdc.gov/safewater/solardisinfection.html https://www.cdc.gov/safewater/solardisinfection.html) Or it's not the best? (true, but the phrase is not meant literally). Or that the figurative meaning is wrong - that "shining a light" on shady or immoral acts and behaviors is not "the best" for some sense of that word, and there are better options? https://sunlightfoundation.com/2009/05/26/brandeis-and-the-history-of-transparency/ https://sunlightfoundation.com/2009/05/26/brandeis-and-the-h... is an interesting blog post on the author of the phrase.