The SloMo Guys (primarily Gav) demonstrate how a television works using cameras with a high shutter speed. Contrary to what you might assume, the image on a TV is not replaced all at once. Rather the pixels are changed very quickly line by line (from left to right) and from top to bottom. Moreover, the pixels on the screen don't completely turn off for non-OLED (organic light emitting diode) displays. This is why OLED displays can show deeper colors (primarily blacks) as compared with other displays and can be made thinner. The thinness comes from not having to keep all the pixels backlit for the entire display.