“as clear as day”别理解成“像白天一样清楚”，真实含义是显而易见；容易理解；昭然如日；肯定的。

【例句】
Although it’s written on the door as clear as day, people still don’t realize that this room is private.
虽然它显而易见，但人们还是不知道这个房间是私人房间。

The instructions were as clear as day. You can read them before you use it.
使用说明上写得清清楚楚。使用之前你可以来用一下！