What the app reads from Apple Health
Exactly which data is used, and what is never touched.
What is read
Sleep duration and sleep efficiency. Nothing else. The permission dialog asks for Sleep Analysis and the app requests read access only.
What is never read or written
Heart rate, activity, workouts, weight, and every other Health category. The app also never writes to Health.
Turning it off
Revoke the permission in Health at any time. The lamps carry on running their curve; only the personal calibration stops updating.