# Experimental Study on Chromaticity Control in Visible Light Communication Systems
## 3 Research on RGB LEDs Dimming
### Dimming Experiment
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**RGB Proportion** & \begin{tabular}{c} **Measured Color** \\ **Temperature (K)** \\ \end{tabular} & \
\begin{tabular}{c} **Calculate Color** \\ **Temperature (K)** \\ \end{tabular} &
\begin{tabular}{c} **Color Temperature** \\ **Difference (K)** \\ \end{tabular} \\ \hline
0.557:0.301:0.142 & 2539 & 2500 & 39 \\
0.502:0.280:0.218 & 3030 & 3000 & 30 \\
0.476:0.347:0.177 & 3525 & 3500 & 25 \\
0.439:0.304:0.257 & 4012 & 4000 & 12 \\
0.417:0.370:0.213 & 4532 & 4500 & 32 \\
0.405:0.323:0.272 & 5023 & 5000 & 23 \\
0.382:0.361:0.257 & 5510 & 5500 & 10 \\
0.364:0.356:0.281 & 6032 & 6000 & 32 \\
0.347:0.363:0.290 & 6526 & 6500 & 26 \\
0.336:0.355:0.308 & 7036 & 7000 & 36 \\
0.313:0.382:0.305 & 7540 & 7500 & 40 \\
0.302:0.381:0.317 & 8032 & 8000 & 32 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison between measured data and calculated data. Figure 10: Curve of color coordinates changing with color temperature between measured and calculated values. (**a**) Curve of color coordinates changing with color temperature. (**b**) Color temperature error curve. The HP350 spectral illuminometer is used to measure the luminous flux, irradiance, color tolerance, light intensity, and a color index of the mixed light source. In Figure 12, it can be seen that the maximum luminous flux set in the experiment is 100 lm, and the luminous flux of the mixed light varies between 92 lm and 100 lm. The resulting luminous flux of the mixed white light is relatively high, and when adjusting the color temperature, the fluctuation of the luminous flux is very small, with a fluctuation of 2.24%. Therefore, the influence of color temperature on the luminous flux is relatively small, which is consistent with the simulation results. The irradiance range of mixed white light is 3.4 W/m\({}^{2}\)\(\sim\)4.2 W/m\({}^{2}\). When the color temperature range is 5000 K\(\sim\)6500 K, the irradiance reaches the maximum, and the lighting effect is the best. The color tolerance Duv is stable at around 0, which is specified to be less than 5.5 \(\times\) 10\({}^{-3}\) and can meet the lighting standards [28]. In Figure 13, it can be seen that the illumination value fluctuates less with the change in color temperature, with a difference of only 8.2 k between the maximum and minimum values. The change in color temperature has a small impact on the illumination intensity, which confirms the conclusion of the simulation. In Figure 13, the comparison between the calculated color index and the measured color index according to Equations (6) and (7) shows that the theoretical value of the color index is in good agreement with the measured value. The color index is greatly affected by the color temperature. When the color temperature is within the range of 5500 K\(\sim\)6500 K, the color index is the best. This color temperature range is the light and color temperature at noon. The effect of restoring the color of the object itself is the best, which also conforms to natural law. The light source  
Figure 11: Duty cycle of RGB LEDs varies with different color temperatures. Figure 12: Variation of luminous flux, irradiance, and color tolerance with color temperature. with a color index of more than 75 is a high-quality light source [29]. The color index of the mixed white light is more than 76 within the adjustable color temperature range, and the maximum color index is 92, indicating that the experimental mixed white light effect is good. Using the HP350 spectral illuminometer to measure the light intensity at different color temperatures and distances, as shown in Figure 14, the curve of light intensity with distance at different color temperatures is shown. The curve of light intensity with distance at each color temperature almost overlaps, indicating that the influence of color temperature on light intensity is not significant.