As in "to scare the living daylights out of" someone. David Crystal writes about this in By Hook or By Crook as follows: "The plural of daylight is known from the eighteenth century. Henry Fielding is the first recorded user, in Chapter 10 of his novel Amelia. During a lively piece of prison table-talk we hear one woman say of another, who has called her a 'good woman': 'Good woman! I don't use to be so treated. If the lady says such another word to me, d—n me, I will darken her daylights.' 'Black her eyes,' we would say these days. Daylights was slang for 'eyes'." (p 71)
Crystal goes on to talk about how "daylights" then came to mean other vital organs, not just they eyes, and says that "the living daylights" "seems to have arisen in the late nineteenth century. It became popular about fifty years later" (ibid.).