## 4 Result and Discussion
### Illumination Performance  
Figure 5 illustrates the illuminance uniformities obtained against varying semi-angles at half power (SAAHP) for all the twelve iterative cases. It can be seen that \(U_{o}\) improves with increasing SAAHP and it is maximum at 70\({}^{\circ}\). Since the LED without optics has SAAHP= 60\({}^{\circ}\), we will limit analysis to 60\({}^{\circ}\) in the following section. The ColQ-based cases, which are closest to the desired uniformity value of 0.7, are the cases III, IV, X, XI, and XII. Here, it is important to state that, according to general indoor lighting placement rules, extreme corner lighting is not preferred and luminaires must be placed at least 0.6-0.9 m away from the corners to avoid wastage of light and unsightly shadows. Accordingly, even though cases XI and XII provide uniformity that is close to the threshold at 60\({}^{\circ}\), these placement locations are not practical signifying that only cases III, IV, IX, and X can be  
Figure 5: Uniformity of illuminance for cases I to XII at varying semi-angles at half power (SAAHP).  
Figure 6: Illuminance histograms for CLQ and ColQ-9.  
considered (denoted hereafter as CoIQ-3, CoIQ-4, CoIQ-9, and CoIQ-10, respectively). Besides, when four transmitters are located close to the geometrical center of the room, uniformity is poor and it worsens with five transmitters, e.g., case-I and case-VII, which represent CLQ with four and five transmitters, respectively. Conversely, CoIQ-based arrangements with five transmitters provide better uniformity, which is relatively lesser with four transmitters. Table 2 summarizes the uniformity and IQR values that were obtained for these cases. The CoIQ cases outperform the CLQ based arrangement in terms of the uniformity of illuminance, with CoIQ-3 offering the best uniformity. CoIQ-10 has the least IQR dispersion, followed by CoIQ-3. However, to establish a comparison of our proposed corner-based placement scheme with the conventional technique, we will use CoIQ-9 as the worst-case scenario with the least uniformity of 0.6594.  
Figure 6 depicts the illuminance histograms that were obtained for the two scenarios under consideration, i.e., CLQ and CoIQ-9. Both the cases satisfy the ISO based average illuminance requirements of 300-500 lux for indoor spaces with average values of 614.17 and 511.27 lux for CLQ and CoIQ-9, respectively. CLQ is spread over a wider range between 200-1000 lux which is reflected in its high IQR value of \(\sim\) 295.82 lux (see Table 2). On the contrary, CoIQ-9 has a smaller spread, with values ranging between 300 and 600 lux and an IQR of only 111.23 lux. Besides, the uniformity values are 0.377 and 0.659 for CLQ and CoIQ-9, respectively. This indicates that even the worst-case scenario of the proposed arrangement has better uniformity than CLQ. Additionally, these values also validate that uniform distribution of illuminance is extremely poor in the conventional CLQ considering that the desired value is 0.7. It also implies that, relative to CLQ, the uniformity in CoIQ-9 has improved by 74.80%. Because CoIQ-9 had been assumed as the worst-case scenario, a further improvement in uniformity is also possible with other CoIQ-cases, i.e., 82.49% with CoIQ-10 and CoIQ-4 to a maximum of approximately 102% with CoIQ-3. However, the analysis of illuminance uniformity is not sufficient to remark on the communication quality of an optical link. Hence, the subsequent subsection will consider the effects of different lamp arrangements on the communication performance.