light at the end of the tunnel 隧道尽头的光；一线希望；苦尽甘来；隧道尽头的曙光；曙光乍现

【例句】
The light at the end of the tunnel is that once I pass my tests, I automatically1 get accepted into university.
给我一线希望的是，一旦通过这些考试，我就自动被大学录取了。

Trust me, when you can see the light at the end of the tunnel, you won't regret spending all day studying.
相信我，当你感到苦尽甘来的时候，就不会后悔整天都在学习了。