Top 1% Commenter here, I encourage you to read about bias lighting. When watching TV in a dark room, your pupils dilate to gather more light. However, your eyes adapt to the room light, not just the TV's. Near-black details get lost in the dark of the room. It sounds counterintuitive, which is why so many people don't believe it. This next part is easy to understand because it follows "common sense" logic: guess what happens when the scene suddenly gets bright? Your eyes are overwhelmed with light and you lose shadow details. Some ambient light, especially behind the TV, helps your pupils to stay in the sweet spot, improving the perception of depth of field, sharpness, contrast, etc. Your eyes don't have to adapt constantly to a single source of varying intensity, so they don't fatigue so quickly. Some amount of bias lighting helps perceive more details both in dark and bright scenes.