HDR films can contain deliberately dark scenes, and a bright room reduces your ability to see shadow detail. Display capability, tone mapping and picture mode also matter. Start by reducing reflections and checking the active HDR preset before changing unrelated black-level controls.
Separate intention from a fault
Compare several scenes and another trusted HDR programme. One night sequence being dark is different from every menu, face and daytime shot appearing unusually dim. If the entire presentation is affected, investigate the display mode and signal path. If only particular scenes are difficult, room lighting may be the main limitation.
Control reflections first
A lamp or window reflected in the screen can hide dark detail even when the panel is working correctly. Move the light source, close curtains or use softer lighting behind the viewing area. Avoid shining a bright light directly at the screen while trying to judge whether its shadows are being reproduced properly.
Use the right brightness control
Televisions use confusing names for backlight output, panel brightness and black level. Read the model’s explanation before changing them. Raising black level can turn blacks grey without making the intended picture clearer. Save the original values and compare a neutral HDR preset with any brighter viewing mode your television documents.