# AR Displays: Next-Generation Technologies to Solve the Vergence-Accommodation Conflict
## 2 General Concept of Wearable AR Display  
One of the key application areas of AR displays is in professional high-complexity work--especially where errors can cause devastating consequences. These are mainly high-complexity or critical tasks, which would greatly benefit from additional helpful information in the field-of-view of the operator. For example, when dealing with the assembly of complex mechanisms with a very high number of parts, it is tedious to consult a separate (written) manual--this can cause errors and greatly slows down the process. By implementing the manual in an easily comprehendible digital-assembly assistant, which is viewed in real-time through means of AR display, the pace of process would increase, the number of errors would decrease, and the overall productivity would be much improved. Similar gains are also expected in medical disciplines, military and tactical tasks, engineering and construction, etc. Moreover, augmented reality displays would open up new possibilities also for creative professions--providing means to view and communicate interior designs, architectural solutions, etc., to other people through augmentation of the actual environment.  
From these examples, it is obvious that many tasks are performed by looking at a close distance--up to an arm's reach. Thus, one of the most important prerequisites of modern AR display systems is capability of displaying a natural-looking 3D image at these short distances. Other things include sufficient field-of-view (FOV), both horizontally and vertically, with high angular resolution. Furthermore, as the display devices could be used indoors as well as outdoors, the ambient light levels would vary greatly. The challenge is to match the brightness of the virtual image to the ambient levels in case of brightly-lit outdoor environments and providing versatility to adopt to low lighting levels without sacrificing light throughput from the real world. The dependent challenges include fitting all the optical and electronics components into a lightweight and compact footprint, optimizing energy consumption and ensuring superb positional tracking/spatial awareness capability, among other more minor issues. Nevertheless, on the background of all things needed, development of optical solutions is still the most challenging and hardest issue.  
In light of this, the approach of wearable AR displays has split into two--smart glasses and more professional work-inclined AR wearable displays or headsets. Nevertheless, it must be noted that this division is rather loose. Typically, what is meant by smart glasses is a small display built into normal-appearance glasses, thus providing a user with a discrete display. Currently these displays are rather rudimentary and intended for depiction of very limited graphical information--mostly pictograms and basic text. Moreover, often these are monocular systems with no means of representing 3D content. The other branch, on the other hand, is true stereoscopic display systems capable of 3D image representation and ensuring spatial tracking, which consequently makes them considerably bulkier. Though not currently, but rather in the distant future, it is envisioned that both of these branches will converge towards a sleek glasses design with full functionality of stereoscopic systems.  
Further we focus only on stereoscopic head-mounted AR displays and ways of improving their image performance.