# Evaluating the Quality of Light Emitted by Smartphone Displays
## 3 Results
### Spatial Radiation Distribution  
The relative luminous intensity distribution curves (Figure 6a,b) were created to compare the spatial radiation distributions of the screens of individual smartphones. The obtained luminous intensity curves show many similarities. First of all, it can be observed that the luminous intensity distributions for all the screens tested are practically identical across different photometric planes, C0-C180 and C90-C270. It means that the luminous intensity distributions of the tested screens are rotationally symmetrical, which aligns with theoretical expectations. Phones with LCDs exhibit a slightly narrower luminous intensity distribution than those equipped with AMOLED displays.  
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Flicker Percent (\%)**} & \multicolumn{2}{c}{**Frequency (Hz)**} \\ \cline{2-5}  & **Energy** & **Normal** & **Energy** & **Normal** \\  & **Saving Mode** & **Mode** & **Saving Mode** & **Mode** \\ \hline
1 & 4.3\% & 3.3\% & 60.0 & 90.0 \\ \hline
2 & 22.3\% & 21.2\% & 60.0 & 120.0 \\ \hline
3 & 6.3\% & 5.1\% & 60.3 & 119.8 \\ \hline
4 & 4.5\% & 4.4\% & 60.1 & 60.  
The entire luminous flux of the displays is emitted into one hemisphere, with the majority of the luminous flux occurring at a solid angle of 100\({}^{\circ}\). For 8 of the tested smartphones (except for sample 8), the luminous intensity values for angles greater than 50\({}^{\circ}\) are less than 20% of the maximum luminous intensity. A division by display technology is also visible in the luminous intensity distribution. LCDs (samples 6 and 9) have a narrower light distribution than phones with AMOLED displays. The phone with the broadest light distribution is one of the oldest devices in the tested group (sample 8).  
The screens of the tested smartphones also differ in maximum luminous intensity, which in each case occurred in the direction normal to the screen surface. The phones' displays reach luminous intensity values from 1.7 cd to 3.9 cd. The lowest maximum luminance was obtained by sample 8, while the highest was obtained by sample 2. These phones have AMOLED displays and belong to the same manufacturer series. However, they differ in their release date. The oldest smartphone obtained the lowest luminous intensity value (sample 9).  
The maximum half-peak divergence (HPD) was defined as the angle from which 50% of the maximum luminous intensity value of the display is achieved. The set of calculated values for these angles, characterizing the spatial radiation distribution, is presented in Table 5. Most phones with AMOLED technology achieved similar values for the HPD based on the average photometric curve. There was a 9\({}^{\circ}\) difference between the maximum and minimum HPD. The average value for smartphones with AMOLED displays was 73\({}^{\circ}\). The best result in this comparison was achieved by sample 8, which directly relates to its wide distribution.  
In contrast, sample 2, although one of the newer models, performed the worst among phones with AMOLED displays. This phone reaches higher luminous intensity values, but its distribution is much narrower and more concentrated. It means that the content displayed on the screen will not be visible from a large angle, which may reduce user comfort.  
A significant difference in HPD was observed for LCDs. For these models, there was a drop of about 22\({}^{\circ}\) compared to the average value obtained by AMOLED displays. The lowest HPD was recorded for the oldest model in comparison (sample 9). Figure 6c compares the biggest and smallest HPD for smartphones in comparison, for samples 8 and 9, respectively.  
Figure 6: The spatial distribution of selected smartphone samples: (**a**) C0-C180, (**b**) C90-C270, and (**c**) comparison between the biggest and the smallest half-peak divergence.