According to the working environment, LED displays can be divided into indoor led screens, outdoor led screens and semi-outdoor led screens. There are some data in theory which can reflect the relationship between the pixel pitch and the best viewing distance.
The relationship between pixel pitch distance and the best viewing distance

In the actual application, because of the limitation of led display installation environment and identify ability, led display’s smallest viewing distance is mean the shortest distance that can identify the text and picture showing. The shortest viewing distance and led specification are on below: