You have the possibility to set manually or automatically the display brightness of your Steel HR / Steel HR Sport. To do so, perform the following steps: 

1. Open the Withings App.
2. Go to Devices.
3. Tap Steel HR / Steel HR Sport.
4. Select More Settings.
   
5. Select Auto-brightness.
   The display brightness of your Steel HR / Steel HR Sport will vary automatically depending on the outside light. 
   
6. If you don't want to select the Auto-brightness mode, move the slider to set manually the display brightness of your Steel HR / Steel HR Sport.

Note: When a workout or sports session is launched on the Steel HR / Steel HR Sport, the display of the watch will remain on, at full brightness, until workout mode is ended. This is normal behavior and does not indicate an issue with the watch.