Diagnosis
Yep, that LED panel is seriously bright for a dark room. Sony didn't include a dedicated dimmer setting, but there's a workaround.
How to Fix It
You can't dim it, but you can turn it off completely. On the remote, press the 'Display' button. Each press cycles through: info on -> info off -> display off. 'Display off' will turn the entire front panel dark. The soundbar will still remember your volume and input settings.
If That Didn't Work
If the 'Display' button isn't responding, make sure you're not on the Bluetooth input ('BT') where the button might have a different function. Switch to 'TV' or 'OPTICAL' input first, then try the Display button.
Heads Up
With the display off, you lose visual feedback for volume changes and input switches. You'll have to go by sound or briefly press 'Display' again to check what's happening.