in the cold light of day

Probably an allusion to a situation being seen more clearly in daylight, and after some time has passed. The word cold is used in the sense of “dispassionate; not prejudiced or partisan; impartial”.[1]

• (Received Pronunciation) IPA^(key): /ɪn‿ðə ˈkəʊld laɪt‿əv ˈdeɪ/
• (General American) IPA^(key): /ɪn‿ðə ˈkoʊld laɪt‿əv ˈdeɪ/
• Rhymes: -eɪ

in the cold light of day

1. Viewed calmly and dispassionately after allowing emotions to cool or after having sobered up.

   Antonym: in the heat of the moment

   In the cold light of day, I felt I had overreacted.

   • 1912 March, Burton E[gbert] Stevenson, “Preparations”, in The Mystery of the Boule Cabinet: A Detective Story, New York, N.Y.: Dodd, Mead & Company, published 1918, →OCLC, page 119:

     In my over-wrought state of the night before, it had seemed reasonable enough; but here, in the cold light of day, it seemed preposterous.

   • 2016, Susan Greenfield, “Dreaming”, in A Day in the Life of the Brain: The Neuroscience of Consciousness from Dawn till Dusk, London: Penguin Books, published 2017, →ISBN:

     To the dreamer, a dream can seem at the time eerily indistinguishable from everyday consciousness yet, in retrospect, upon waking, so self-evidently different. The fragmented narrative, the improbability of much of what happens – flying, for example, or the transmogrification of one individual suddenly into another, and so on – seem ludicrous, even embarrassing, in the cold light of day.

   • 2018 August 16, Marshmello, Steve Mac, Dan Smith (lyrics and music), “Happier”, performed by Marshmello and Bastille:

     In the cold light of day, we're a flame in the wind / Not the fire that we've begun.

2. Used other than figuratively or idiomatically: see in,‎ the,‎ cold,‎ light,‎ of,‎ day: during the day; in daylight.
   • 1853, Anna Mary Howitt, “The Casting of the Sieges-Thor, Bavaria”, in An Art-student in Munich. […], volume II, London: Longman, Brown, Green, and Longmans, →OCLC, page 178:

     And above the crowd of living figures rise colossal forms of armed warriors, and peaceful poets, and sceptred monarchs; these glowing crimson; those standing calm and pale in the cold light of day.

   • 1989, Rüdiger Safranski, “Weimar”, in Ewald Osers, transl., Schopenhauer and the Wild Years of Philosophy, Cambridge, Mass.: Harvard University Press, published 1991, →ISBN, book 1, page 72:

     However subtle the social pecking order may have been, the outsider entering the famous town with high expectations saw it in the cold light of day shrink into a philistine backwoods dump.

• morning after
• at the end of the day

• “in the cold light of day”, in Cambridge English Dictionary, Cambridge, Cambridgeshire: Cambridge University Press, 1999–present.
• “in the cold light of day” (US) / “in the cold light of day” (UK) in Macmillan English Dictionary.
• “in the cold light of day”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.
• “in the cold light of day” in Longman Dictionary of Contemporary English, Longman.