We first had the idea for this night lamp back in 2013. Tyler, our eldest, was two at the time. He'd slept in for the first time--which allowed us to sleep in for the first time! As I recall, we slept passed 8:00 that morning. We felt so good that we wondered how we could get him to sleep longer (or just stay in his bed).
That set us on a journey of trying to understand how we could get him to understand time--and stop waking us up every morning at random times between 5:00 and 6:00.
What we learned was that Tyler was smart. And he was very capable of managing his behavior when he understood a simple expectation.
With respect to rest, he wanted to know why he had to do it and when it would be over.
While he had difficulty understanding an abstract concept like time--and he had little reference for passing time--he could understand the notion of energy.
So we explained the reason for rest in terms of energy...