# Mini-LED and Micro-LED: Promising Candidates for the Next Generation Display Technology
## 2 Mini-LED  
High dynamic range (HDR) is one of the important features for next generation displays [16]. To achieve HDR with contrast ratio (CR) higher than 100000:1, high peak brightness and excellent dark state of the display system are simultaneously required [17]. Although the best requirement for HDR is pixel level dimming, which is described as micro-LED technology, there are still some technological bottlenecks that make micro-LED harder to realize quick commercialization. Therefore, a compromising way to realize multi-zone local dimming for LCD is direct-lit mini-LED backlight. Mini-LED technology has much smaller size of LED, which means it can divide more dimming blocks in a certain size LED backlight. Recently, LED manufacturers have turned to research and develop mini-LED. Most of existing processes and equipment for conventional LED can be used continuously for fabrication of mini-LED. [PERSON] et al. discussed the system modeling and performance evaluation of LCDs with mini-LED backlight [18]. First, a model of LCD system with a direct-lit mini-LED backlight is set up for simulation (Figure 2). The backlight unit consists of square-shaped mini-LED array. A diffuser plate is utilized to widen both spatial and angular distributions, and a liquid crystal (LC) panel is applied to control the output light. The parameters of the model, such as \(p\), \(s\), \(H_{1}\), and \(H_{2}\), are based on the device configuration reported in Reference [19]. To validate the model, four patterns are used to simulate the dynamic CR of the model, and the simulated results can agree with the measured data from Reference [19] reasonably well. Next, the proved model is utilized to find out the relationship between the device structure to the final HDR display performance, especially the halo effect (Figure 3). Final HDR performance of displayed images are calculated via independently adjusting two key parameters of the device  
Figure 1: Forecast about the development of micro-LED displays. Figure 2: Schematic diagram of the model for the LCD with a mini-LED backlight [18]. Figure reproduced with permission from Optical Society of America. structure, the local dimming zone number and the LCD contrast ratio. According to simulation results, the dimming zone number mainly affects the halo area, while LCD contrast ratio influences the local image distortion, and more local dimming zones and higher LC contrast ratio can reduce the halo effect and improve the display performance. Then, a subjective experiment is designed and carried out to determine the human visual perception limit of halo effect. The _LabPSNR_, an evaluation metric used to quantify the difference between displayed image and target image, should be larger than 47.4 dB. Based on this limit, the requirement of local dimming zone number can be proposed: over 200 local dimming zones for high CR \(\approx\) 5000:1 LCD panels and more than 3000 dimming zones for CR \(\approx\) 2000:1 LCDs (Figure 4). Although the above simulations and experiments are all based on the small-size smartphone displays with viewing distance at 25 cm, the analysis and conclusion can also be applied to display devices with different sizes and resolutions via converting the results from spatial domain to angular domain (Figure 5). In summary, [PERSON] et al. demonstrated the required local dimming zone number to exhibit comparable HDR performance with OLED, and the HDR performance could not be achieved  
Figure 4: Simulated _LabPSNR_ for different HDR display systems with various local dimming zone numbers and LC contrast ratios [18]. Figure reproduced with permission from Optical Society of America. Figure 3: Displayed image simulation: (**a**) Mini-LED backlight modulation; (**b**) luminance distribution of the light incident on LC layer; and (**c**) displayed image after LCD modulation [18]. Figure reproduced with permission from Optical Society of America. by conventional segmented LED backlight.