Is it an LG? If so, you might have it in energy-saving mode, which I believe automatically dims the screen. Go into your settings and look for something that says Eco mode, energy-saving mode, green mode or something similar and turn it off. I know Sony makes OLED TVs too, but I'm not familiar with those. They could very well have a similar setting that's the culprit. You could also check with Best Buy about the settings they used in their model T.V. Store lighting is very different so that could be playing a role in your perception as well.