The Philips health watch is designed to also be worn at night to allow automatic sleep tracking. If you are interested in collecting more sleep related information (for example the time to fall asleep), you can manually start the sleep mode when you intend to fall asleep, and stop the sleep mode at the moment of waking up in the morning.

To activate sleep mode select Sleep from the menu and press the play icon. The watch will automatically estimate the moment when you actually fall asleep. Press the stop icon when you wake up without the intention to resume sleep.

The sleep processing service requires some time to calculate sleep duration and efficiency. As a result, if you have not turned on Sleep mode,  and sync in the morning, you won’t see your sleep data right away. If this is the case check again after an hour. 

Note: in order to see sleep efficiency you need to turn Sleep mode on when you intend to sleep.