## 3 Numerical Results
### Effect of Available Emitted Power
Simultaneously, the achievable rate performance metric is enhanced to 11.31 Bits/Hz, 3.27 Bits/Hz, and 7.71 Bits/Hz, from the initial 4.67 Bits/Hz, 0.0066 Bits/Hz, and 1.22 Bits/Hz for the Z-Power drone VLC, NSPW  
Figure 6: **(a)** Achievable rate performance of side position for light receiver versus the total available signal power and **(b)** energy efficiency performance of side position for light receiver versus the total available signal power. drone VLC (side position), and NSPW drone VLC (side position 2), accordingly. When the available signal power is increased to 1000 mW from the initial 100 mW, the achievable rate gain provided by the Z-Power beam drone VLC is varied to 2.62 Bits/Hz from the initial 2.58 Bits/Hz, compared with the Lambertian drone VLC, since the unique emission characteristic of Z-Power light beam is capable of radiating more signal power to the non-terrestrial space where the aerial receiver is located. Note that, in Figure 6a, the curves of 0.85 m and 2.5 m for the Z-Power light beam are highly overlapped, which indicates that excellent coverage consistency could be provided by the Z-Power light beam-based drone VLC for the terrestrial light receiver and the aerial light receiver. On one hand, the energy efficiency of drone VLC under different light beam configurations is degraded to some extent separately, as shown in Figure 6b. Particularly, for the situation of receiver altitude of 0.85 m, the energy efficiency performance of baseline Lambertian light beam configuration based drone VLC is degraded to 13.03 Bits/J/Hz from the initial 63.83 Bits/J/Hz, when the total available signal power at the transmitter of drone VLC is increased to 1000 mW from the initial 100 mW. At the same time, the energy efficiency performance metric is reduced to 11.31 Bits/J/Hz, 11.53 Bits/J/Hz, and 14.40 Bits/J/Hz, from the initial 46.71 Bits/J/Hz, 48.86 Bits/J/Hz, and 77.56 Bits/J/Hz for the non-Lambertian Z-Power light beam configuration, non-Lambertian NSPW light beam (side position), and non-Lambertian NSPW light beam (side position 2), accordingly. This means that compared with the baseline Lambertian configuration-based drone VLC, the energy efficiency gain provided by the non-Lambertian NSPW beam-based drone VLC (side position 2) is varied to 1.37 Bits/J/Hz from the initial 13.73 Bits/J/Hz, when the total available signal power is increased to 1000 mW from the initial 100 mW. As for the situation of receiver altitude of 2.5 m, the energy efficiency performance of baseline Lambertian configuration-based drone VLC is degraded to 8.69 Bits/J/Hz from the initial 20.89 Bits/J/Hz, when the total available signal power of drone VLC is increased to 1000 mW from the initial 100 mW. Simultaneously, the energy efficiency performance metric is reduced to 11.31 Bits/J/Hz, 0.066 Bits/J/Hz, and 7.71 Bits/J/Hz, from the initial 46.67 Bits/J/Hz, 3.27 Bits/J/Hz, and 12.16 Bits/J/Hz for the non-Lambertian Z-Power light beam configuration, non-Lambertian NSPW light beam (side position), and non-Lambertian NSPW light beam (side position 2), accordingly. This demonstrates that compared with the Lambertian configuration-based drone VLC, the energy efficiency gain provided by the non-Lambertian Z-Power beam-based drone VLC varied to 2.62 Bits/Hz from the initial 25.78 Bits/Hz, when the available signal power is increased to 1000 mW from the initial 100 mW. The above figures of the emitted power effect indicate that with the increase in the total available signal power, the growth rate of the achievable rate is slowed down, and the energy efficiency performance is accordingly degraded. Note that under different altitudes, the best performance consistency could still be provided by the Z-Power non-Lambertian drone VLC, thanks to its superior performance in lighting the different domains simultaneously. To help readers grasp the overall trends and identify key findings of the emitted power effect more effectively, a summary of the results is presented in Table 5 as follows: