Contrast in advertising LED screens is the maximum difference between brightness intensity in the range of targets compared to the range of blacks.The contrast ratio is expressed as a ratio of type X: 1 and shows the difference between the brightest white and the darkest black that can be seen on the advertising LED screen.
The higher the system’s ratio the more ability to reproduce intermediate tones it will have, thus offering a better dynamic range and a greater capacity for color reproduction.
The real contrast measures the difference between a black and a white pixel in a single instant, and its figures are usually low (800: 1, 1000: 1, 1600: 1, …). You must look at this figure if you are going to use your screen for static images such as graphic design or photo editing.
On the other hand, the dynamic contrast is a measure of convenience among manufacturers that measures the variation of a pixel from black to white (or between greys) in a period of time. This figure does not depend on physical technology, like real contrast, but on software algorithms and image treatment. Their figure is usually much higher than the real one (20000: 1, 50000: 1, 100,000: 1 or even higher). The dynamic contrast ratio is a fairly relative measure, but it can be useful to measure how good contrast can be in moving images.
At present, indoor LED screens have been designed with SMD LEDs that are commercially called Black LED (there are other trade names), where the coating resin has been tinted in a black or a dark tone. In this way, the contrast of the image is increased when it tends to black. However, its contrast is penalized when it tends to white colour, so the contrast levels remain the same, so it is more of a marketing tool than an important value to consider.