# Refined Test and Evaluation Method of Side Viewing Angle of LED Display Module
## 1 Introduction  
Light-emitting diodes (LEDs) are widely used in lighting and display fields due to their high brightness and low power consumption [1]. The uniformity of LED display products is mainly reflected in three aspects: brightness, chromaticity and viewing angle characteristics. The brightness and chromaticity can be improved using the method of correction. Due to the optical properties of the LED light-emitting tube, each LED light-emitting tube presents different light intensity distributions at multiple angles in space. This problem depends on the structure of the packaged semiconductor chip and the packaging form of the LED [2, 3]. Displays with too large a range of luminescence direction specificity cannot be changed even by correction.  
The LED large screen is assembled and spliced by the display unit (hereinafter referred to as the display module). Due to the different spatial angle light intensities of the LED light-emitting chip and the difference in the production process, the luminance and color of the display module at different viewing angles are different, resulting in inconsistencies in the display angle of the displayed image [4]. Therefore, the inconsistency of the viewing angle of the display screen has become an important factor affecting the quality of the display screen. [PERSON] analyzed the influence of viewing angle on the brightness uniformity of the display screen and came to the conclusion that, the more the viewing angle deviatesfrom the normal direction, the worse the display screen uniformity is and proposed a display screen uniformity evaluation method based on temperature and viewing angle [5]. [PERSON] et al. proposed a simple, low-cost method to enhance angular color uniformity of color-mixed light-emitting diodes by introducing a diffuse coating layer [6]. [PERSON] et al. proposed a full-color viewing angle compensation algorithm for the brightness difference at the splicing of the cabinets, which compensates the RGB three-color image pixel by pixel [7]. The above literature all show that consistency of the display viewing angle has always been a difficult problem to solve in the industry. In this paper, starting from the direction of the spatial distribution of the luminous characteristics of the display unit, theoretical analysis and testing are carried out to evaluate the specificity, so as to screen and classify the display modules to improve the display uniformity of the display screen.  
The display effect is closely related to human visual characteristics [8]. According to [PERSON]'s law, human eyes are sensitive to relative luminance deviation rather than to absolute luminance deviation. Too high a background brightness will reduce the human eye's perception of non-uniform defects on the screen [9]. Therefore, in this paper, the relative brightness differences of luminescent units in the range of horizontal viewing angles were evaluated by combining the characteristics of human vision, and the display units were classified and the display brightness uniformity was evaluated based on the influence of the side view on the observers. This study has guiding significance for the production process control of LED display modules.