# High-Resolution Pixel LED Headlamps: Functional Requirement Analysis and Research Progress
## 3 Research Progress of High-Resolution Headlamps
### Review on High-Resolution Headlamp Prototypes  
The following review is based on the published prototypes of high-resolution headlamp and their features in the Table 1.  
With the development of miniaturization and intelligence of automobile styling, LEDs are widely used in the field of automobile lighting due to their high brightness, miniaturization, and functional integration. In order to maintain the specified luminous flux output of the system, the size of the LED light source will be scaled or increased accordingly to compensate for the low efficiency of the entire optical system, which requires the LED to have high flexibility.  
The LED array has a small number of pixels and relatively low resolution, which can achieve basic far and near beam lighting and anti-glare functions. Additional colors of LEDs can be added to adapt to the disadvantage of poor white light penetration in bad weather. Each LED in the LED array needs to be controlled individually, which increases the size of the system and limits the number of LEDs. Improving optical efficiency and good thermal performance are the main challenges, which requires the LED array to be compact, which brings new challenges to the underlying technology. The integration of additional functions further promotes the miniaturization of the light source. At present, LED array-based modules generally use a dense secondary optical collection system and generally use a conical light collector or a silicone lens, which limits the volume of the entire system.  
The new technology has increased the resolution to far more than 10,000 pixels. Due to the development of micro-LED technology such as micro-led, LED technology can be miniaturized to produce small pixels. Each pixel is closely spaced. The CMOS integrated electrical mutual pass switch can directly address each pixel, the resolution is less than that of the human eye, and it can make the car headlight project each pattern like a projector.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Title 1** & **Number of Pixels** &
\begin{tabular}{c} **Angular Resolution** \\ **in**\({}^{\circ}\) \\ \end{tabular} & **Pixel Pitch in**\(\upmu\) \\ \hline LED array & & & \\ Gordon et al. [39] & \(3\times 11\) & 1.5 & \\ Audi [40] & 25 & & \\ Smartrix [41] & \(3\times 12\) & & \\ Hella [42] & 84 & & \\ Pixel LED & & & \\ Osram [44; 45] & \(32\times 32\) & 0.25 & 125 \\ Trommer [46] & 4096 & 0.25 & 125 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Properties of published prototypes of high-resolution headlamps.  
Figure 9: HD lighting technology: analysis of advantages and disadvantages.  
However, due to the immaturity of the chip manufacturing process, the main challenges are contrast and overall efficiency. The pixel size is small, but the optical separation space between the pixels is difficult to solve. The increase in operating current density will reduce the overall efficiency, and the edge pixel array the photon extraction combined with non-radiation will further reduce the efficiency. One method is to enlarge the pixels, but it will increase the cost of the system. In addition, the difficulties that need to be overcome are the need to change high LED fit and high production volume from the existing technical methods, the extremely high yield requirement, the defect control to avoid bad pixels, etc.  
However, it is foreseeable that, with the development of technology, these challenges can be solved, and micro-led is currently the most effective and lowest cost technical solution.