Hi Ak,
If the image appears too dark, we suggest disabling certain energy-saving features, which can automatically adjust brightness and affect how the screen looks.
Go to: Settings > All Settings > General & Privacy > Power and Energy Saving, then turn off Brightness Optimization, Energy Saving Solution, Motion Lighting, and/or Contrast Enhancer.
To fine-tune brightness, go to: Home > left directional key > Settings > All Settings > Picture > Expert Settings, then adjust the Brightness level (0–50) to your preference.
~Samsung Advisor