Note : HDR is not to be confused with 4K. 4K is an indication of the number of pixels of a screen, which primarily provides more sharpness and detail. HDR is a special technology focusing on colour, contrast and detail. Not all 4K models support HDR.
The human eye captures the brightest white and darkest black. The way we see colours and the brightness of these colours is the foundation of a “realistic” image.
The light output of the TV display is measured in amount of “nits” (candela per m2). When capturing image on camera, the latest technology allows recording of higher nit levels. This results in more realistic picture content, closer to the brightness and darkness levels which the human eye can register.
HDR (High Dynamic Range) is a technique that presents a higher contrast in images, mainly due to wider range of light levels that can be shown. When HDR content is played, the high resolution picture additionally has a high contrast that show more details in bright or dark coloured-images.