A:Answer A 4K screen will typically consume more power than a FHD screen regardless of the technology. More pixels are being pushed by the system. The difference depends upon usage, brightness, material being viewed, game configuration, etc. To reduce that difference one could configure the 4K OLED to run in a "dark mode" using less white thus turning on less pixels and saving some battery life.
An explanation: To create black with AMOLED the pixel is simply not turned on -- there is no backlight. To create black with WLED the computer must consume power to block the WLED backlight.