Table 2:
Mean absolute percentage errors (%) in the visible range due to shadow effects and combined shadow and BRDF effects. Conversion from Lp to Eg are provided with Eq. 6 and Eq. 7. Smallest errors for each sky condition and plaque are formatted in bold. Numbers in parenthesis are the standard deviations. Statistics calculated over all simulations included in each evaluation and over all visible wavelengths.
| Conversion | Measurement | Shadow | Comb., White PTFE | Comb., Grey PTFE | |
|---|---|---|---|---|---|
| BRDF (Eq. 6) | θv = 0° | Clear* | 0.59(±0.26) | 0.95(±0.44) | 0.38 (±0.42) |
| OC | 5.74† | 11.06(±0.13) | 0.77 † | ||
| θv = 40° | Clear* | 0.38 (±0.17) | 0.44 (±0.21) | 1.49(±1.03) | |
| OC | 3.02 † | 4.34(±0.06) | 20.84† | ||
| Lambertian (Eq. 7) | θv = 0° | Clear* | 0.59(±0.26) | 2.51(±1.46) | 4.25(±2.11) |
| OC | 5.74† | 4.61(±0.02) | 7.16† | ||
| θv = 40° | Clear* | 0.38 (±0.17) | 1.22(±0.71) | 9.92(±5.92) | |
| OC | 3.02 † | 1.91 (±0.06) | 5.98† | ||
Clear skies for 20° ≤ θs ≤ 60°.
Standard deviation of shadow effects for OC is zero since the relative sky radiance distribution for OC is independent of wavelength. For the combined effects of BRDF and shadow for the grey plaque under OC, standard deviation is zero because the normalized BRDF of grey plaque is assumed to be independent of wavelength in this study.