If you think about something in the cold light of day, you think about it clearly and calmly, without the emotions you had at the time it happened, and you often feel sorry or ashamed about it.

The next morning, in the cold light of day, Sarah realized what a complete idiot she had been. 第二天早上，莎拉回过头来冷静地想了想，意识到自己当时是多么的愚蠢。