8th&up 
 The second book in the Lux series is even better than the first. It luckily breaks away from the Twilight formula (for the most part), and Armentrout really starts to show her stuff. My three favorite elements of the story are...Katy: she's finally coming into her own, The action: suspense and relationship-wise, things definitely rev up, and Daemon: he is utterly, absolutely scrumptious! 
 Bring on the next volume!