# Perceived Brightness and Resolution of Holographic Augmented Reality Retinal Scan Glasses
## 5 Conclusions  
We found a physical derivation for the perceived brightness and ambient contrast ratio of holographic augmented reality retinal scan glasses. Building on those results, we designed and conducted a psychophysical study to determine the perceived resolution of a fully functional retinal scan glasses prototype.  
The perceived brightness as quantified by the retinal scan luminance L\({}_{\text{RS}}\) changes with pupil size: it increases for small pupils and decreases for large pupils. As a result, retinal scan displays appear brighter in bright environments and darker in dark environments in comparison to conventional displays. This is a unique and advantageous property of retinal scan glasses for augmented reality use cases.  
The psychophysical study produced consistent perceived resolution thresholds of about seven cycles per degree across all trials despite varying background and stimulus conditions. This result shows that within the range of parameters we tested, the optical resolution of the retinal scan glasses and not the human visual perception was the limiting factor for the perceived resolution. Overall, this study demonstrated how both the display and the background can be included in a psychophysical experiment to better understand and optimize augmented reality display performance for realistic use cases.  
Conceptualization, M.R.; methodology, M.R. and P.N.; software, P.N. and M.R.; validation, M.R. and P.N.; formal analysis, M.R. and S.P.; investigation, P.N. and M.R.; resources, S.P. and T.S.; data curation, P.N. and M.R.; writing\(-\)original draft preparation, M.R.; writing\(-\)review and editing, M.R., P.N., S.P., and T.S.; visualization, M.R.; supervision, S.P. and T.S.; project administration, M.R.; funding acquisition, M.R. All authors have read and agreed to the published version of the manuscript.  
Bosch Sensortec supported this study and itself acknowledges financial support for the development of the augmented reality glasses by the Federal Ministry for Economic Affairs and Climate Action on the basis of a decision by the German Bundestag and by the Ministry for Economic Affairs, Labor and Tourism of Baden-Wurttemberg based on a decision of the State Parliament of Baden-Wurttemberg as well as co-financed with tax funds on the basis of the budget financed by the European Union\(-\)NextGenerationEU.  
This study was conducted in accordance with the Declaration of Helsinki and approved by the ethics committee of the Medical Faculty of the University of Tubingen (Code 410/2022B02, Approval 30 August 2023).  
Informed Consent was obtained from all subjects involved in this study. Written informed consent has been obtained from the participant identifiable in Figure 4 to publish this paper.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
We thank [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and the entire Bosch Sensortec optical engineering team for many fruitful discussions and technical support during this study. We acknowledge support from the Open Access Publishing Fund of the University of Tubingen.  
[PERSON], PN, and [PERSON] were employed by Bosch Sensortec GmbH, Reutlingen, Germany, during the creation of this work. [PERSON] and [PERSON] filed patents for Bosch Sensortec GmbH on retinal scan glasses technology. TS declares no conflicts of interest.  
The following abbreviations are used in this manuscript:  
R Retinal Scan  
HOE Holographic Optical Element  
ACR Ambient Contrast Ratio