# Measurement of Circadian Effectiveness in Lighting for Office Applications
## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Workplace** & \(\mathbf{E_{LMK}^{-10^{\circ},\circ}}\) **in lux** & \(\mathbf{E_{LMK}^{-10^{\circ},120^{\circ}}}\) **in lux** & \(\mathbf{E_{LMK}^{-10^{\circ},CE}}\) **in lux** & \(\mathbf{CS_{LMK}^{-10^{\circ},\circ}}\) & \(\mathbf{CS_{LMK}^{-10^{\circ},120^{\circ}}}\) & \(\mathbf{CS_{LMK}^{-10^{\circ},CIE}}\) \\ \hline
#1 & 324.4 & 192.0 & 185.7 & 0.325 & 0.242 & 0.237 \\
#2 & 353.8 & 223.7 & 212.5 & 0.342 & 0.270 & 0.262 \\
#3 & 306.3 & 178.0 & 191.4 & 0.293 & 0.206 & 0.211 \\
#4 & 314.7 & 169.0 & 190.7 & 0.301 & 0.210 & 0.222 \\
#5 & 317.4 & 195.7 & 186.6 & 0.316 & 0.238 & 0.230 \\
#6 & 334.6 & 205.3 & 185.3 & 0.326 & 0.246 & 0.229 \\
#7 & 338.7 & 203.0 & 188.5 & 0.324 & 0.242 & 0.229 \\
#8 & 305.8 & 158.8 & 151.4 & 0.295 & 0.193 & 0.183 \\
#9 & 269.9 & 148.6 & 149.1 & 0.234 & 0.129 & 0.127 \\ \hline
**average** & **318.4** & **186.0** & **182.4** & **0.306** & **0.220** & **0.214** \\ SD & 22.7 & 22.9 & 18.9 & 0.030 & 0.039 & 0.037 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of the illuminance and CS values calculated from the spatially resolved light measurements for the different FOV definitions and a non-zero tilt angle \(\alpha=-10^{\circ}\). reliable and meaningful estimates of the circadian effectiveness of the lit working environment adopting the novel measurement approach proposed in this work, but may also contribute to the optimization of the respective luminaires' light distributions to match the specific, task-related visual needs of the office workers [13]. Their development will be part of our future research efforts. Regarding the specific metric used for estimating circadian effectiveness in the lighting context, it would certainly be beneficial to also consider alternative measures alongside CS, which for practical reasons was within the focus of the present work. The Commission Internationale de l'Eclairage (CIE) recently published the new CIE S 026/E:2018 standard [15], which defines the basic metrology to describe the ability of optical radiation to stimulate each of the five photoreceptor types that can contribute via the ipRGCs to retina-mediated non-visual effects of light in humans. In this context, the melanopic equivalent daylight (D65) illuminance (melanopic EDI) has been proposed--similar to CS--as a metric for the prediction of the circadian impact of the environmental illumination, in particular to guide future health-related lighting design [103; 104]. However, in contrast to the CS metric, for which [PERSON] et al. developed the approximation method of Equation (5), no such simplification using standard photometric and colorimetric quantities has yet been established for the melanopic EDI measure, which, in its current form, is therefore unsuitable for being used within the new spatially-resolved light measurement framework proposed in this work. Nonetheless, future research to describe the circadian effectiveness of lighting should also focus on such CS alternatives that show a comparable predictive performance over a wide range of conditions [103]. Current restrictions of the proposed methodology can mainly be attributed to the fact that there is no applicable and validated recommendation on how to properly weight light contributions from different directions to obtain a truly reliable estimate of the overall circadian effectiveness of a lighting condition. As long as such a weighting scheme has not been fully established, the present work still appears to be limited in its practical relevance. However, it should again be stressed that the proposed framework can easily be extended and adapted accordingly to comply with any desired weighting scheme. A further limitation of the proposed approach can yet be identified in the increase of the model uncertainties for chromatic content. As discussed in Section 3, corresponding error estimates rise considerably when the amount of colored, non-achromatic information becomes predominant in the illuminated scene to be captured.