To put the ONE into sleep mode please keep the Power/Sleep button pressed for 1-3 seconds and the LCD will turn off. If you keep the Power/Sleep button pressed beyond that point (about 10 seconds) the unit will perform a soft reboot.
You can also make sure the ONE goes automatically into sleep mode at a specific time by enabling the POWER SAVER TIME (Settings > Preferences > Power & Sleep).
Your ONE will transition through different stages like LCD off, Hard Drive off, then main PCB off in order to arrive at the final state. When the ONE arrives at the final state, the power LED will “breathe” to indicate that it is sleeping. While in transition, the power LED will remain on.
Note: If any processes are active (i.e streaming from network, playing music, importing music etc.) the ONE will not go into deep sleep mode until these processes are terminated (the LCD however will still turn off).