Before relying on information from the AR view, you should check the calibration by comparing the current location of the sun or moon to the projected location for the current time and date. If they line up, your sensors are calibrated and the other projections should be reliable. If they're off by just a little bit, the sensors are probably as close as they can get in the current environment and you can use the visual calibration feature to "close the gap" and get a perfect projection.
On the other hand, if they're off by a lot you'll probably want to force an immediate sensor calibration. There are a couple of ways to do that, but the most reliable is to open the system Compass app that came pre-loaded on the phone and calibrate from there. When you re-open Lumos you should see a much more accurate projection.
If neither the sun nor moon is currently visible, or if the sun is directly overhead (e.g. at noon near the equator), this strategy won't work. In that case I would always recommend performing a calibration before using the app, just to be safe.
If any of this is unclear, or if you have any additional questions, please send us a message.
P.S. one more tip: the map view does not rely on the device sensors, so it should always be accurate. If there are any recognizable landmarks around you, you can also use the map view to check where the sun will rise/set in relation to them, and then verify whether the augmented reality projection agrees with the map view. If they are different, that's another indicator that your sensors need to be calibrated.