# Evaluating the Quality of Light Emitted by Smartphone Displays
## 3 Results
### Luminance Distribution and Its Uniformity  
An example of the luminance distribution measurement and its uniformity is presented in Figure 7. The exact summary of the average luminance values and uniformity for the various test screens (red, green, blue, and white) can be found in Table 6. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Half Peak Divergence (\({}^{\circ}\))**} \\ \cline{2-4}  & **C0** & **C90** & **Mean** \\ \hline
1 & 78 & 75 & 77 \\ \hline
2 & 73 & 75 & 74 \\ \hline
3 & 73 & 73 & 73 \\ \hline
4 & 73 & 73 & 73 \\ \hline
5 & 70 & 74 & 72 \\ \hline
6 & 72 & 70 & 71 \\ \hline
7 & 66 & 69 & 68 \\ \hline
8 & 48 & 54 & 51 \\ \hline
9 & 53 & 47 & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of half peak divergences (HPD) for light distribution from sample displays. Figure 7: The exemplary luminance distribution measurements outcome, including mean luminance, and uniformity (values in cd/m\({}^{2}\)). The average luminance values for the white screen ranged from 292 to 437 cd/m\({}^{2}\), depending on the type and age of the model. LCD displays (samples 6 and 9) achieved the highest values of this parameter. One of the newest models with an AMOLED display obtained a similarly high result, released in 2023 (sample 2). Most smartphones with this display type achieved values approximately equal to 350 cd/m\({}^{2}\). The lowest luminance for the white screen was obtained by sample 8, the oldest model with an AMOLED display. The smartphone screen's high average luminance value can positively affect display visibility during the day. However, it may also negatively impact the use of smartphones at night [48,49]. The tested samples exhibited average uniformity values between 0.73 and 0.92, averaging 0.83. The highest uniformity values were achieved by two smartphones: sample 1, the newest model in the set, and a slightly older, mid-priced model--sample 4. All smartphones released after 2019 achieved average uniformity values better than the set's average. Sample 9, the oldest model, achieved the worst result and was the only smartphone to record a value of 0.75 or below in each of the R, G, and B channels and for white light. Surprisingly low values were also noted for sample 7 (the flagship smartphone from 2017), as an older and more budget model outperformed it. Smartphones with LCDs showed low red luminance values. Their values were nearly twice as low as the average results obtained by phones with AMOLED displays. However, sample 9 reached a very high blue luminance value, which was more than twice as high as the blue luminance of the newest smartphone in the set. No similarities were observed for the newer smartphone with the same type of display (sample 6), which had blue luminance values close to those of phones with AMOLED displays. A significant difference was also observed between the green and white luminance for the LCD models. It is likely why the white screen luminance reached much higher values. For sample 9, the white screen luminance was 26% higher than the green luminance, while for sample 6, it was 37% higher. The luminance values of the aforementioned green and white screens were similar for AMOLED smartphones. However, the green screen luminance often reached higher values than the white screen luminance. This situation was not observed for the two newest models in the set (samples 1 and 2), where, despite achieving similar values, the white screen luminance was higher.