How do I get DS1 to listen to his sleep cues?

[NotQuiteCockney]

DS1 is 7. He likes to read. We turn his lights out, he reads by the streetlight out the window, or uses whatever toys have lights on them to keep reading.

And then, in the morning, he has big black circles under his eyes, and I have to work pretty hard to wake him.

I'm tired of this struggle, and I'd like to transition to him choosing when to go to sleep, but ideally without him failing utterly from sleep deprivation.

(DS2 is 4. He chooses when he goes to sleep. Go figure.)

Hum. I always used to read by the streetlight/landing light/whatever and it prob did my (already poor) eyesight no good whatsoever... could you agree that he can read for say an hour once he goes to bed (with the light on) as long as he then goes to sleep? And if he reads afterwards his time gets cut the next night?

Oh, I've looked it up, and reading by poor light causes temporary eye strain, but not actual damage (despite what I was told as a child - I did the same).

Thing is, I'd like him to decide when it's time to turn out the light, so he learns how to tell when he's tired enough ...