The brightness of the lighting LED can be adjusted between 4 levels. The brightness can also be synchronized to the brightness of the display.
Switching the display off reduces a source of noise that affects sound quality, enabling higher sound quality playback.
The brightness is synchronized to the brightness of the display. link
Bright / Dim / Dark / Off
When the display brightness is set to off using the DIMMER button, the lighting LED turns off regardless of the “Lighting” setting. link