. Author manuscript; available in PMC: 2022 Feb 14.

Published in final edited form as: Appl Opt. 2019 Jun 1;58(16):4497–4511. doi: 10.1364/AO.58.004497

Table 1:

Mean absolute percentage errors (%) in the visible range due to BRDF effects for two conversion schemes from L_p to E_g represented by 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		White PTFE	Grey PTFE
BRDF (Eq. 6)	θ_v = 0°	Clear^*	0.41(±0.26)	0.66 (±0.35)
	θ_v = 0°	OC	5.68(±0.14)	5.35^†
	θ_v = 40°	Clear^*	0.16 (±0.09)	1.74(±1.26)
	θ_v = 40°	OC	1.55(±0.07)	24.40^†
Lambertian (Eq. 7)	θ_v = 0°	Clear^*	2.69(±1.67)	3.91(±2.08)
	θ_v = 0°	OC	1.16(±0.03)	1.43 ^†
	θ_v = 40°	Clear^*	1.26(±0.66)	9.74(±5.77)
	θ_v = 40°	OC	0.95 (±0.07)	3.22^†

Clear skies for 20° ≤ θ_s ≤ 60°.

^†

Standard deviation is zero since both relative sky radiance distribution for overcast conditions and the normalized BRDF of grey plaque are independent of wavelength.