Table 2 Illuminance values calculated from the angular luminance distribution for a clear and overcast night near Bonnievale, South Africa.

From: Using all-sky differential photometry to investigate how nocturnal clouds darken the night sky in rural areas

 

clear

clouds

horizontal illuminance [mlx]

average (full data)

0.96 ± 0.10

0.76 ± 0.08

NE segment (*)

1.07 ± 0.11

2.55 ± 0.26

SW segment (*)

0.93 ± 0.09

0.34 ± 0.03

SQM (**)

0.91 ± 0.10

—

scalar illuminance [mlx]

average (full data)

1.98 ± 0.20

1.95 ± 0.20

NE segment (*)

3.20 ± 0.32

11.26 ± 1.13

SW segment (*)

1.77 ± 0.18

0.56 ± 0.06

SQM (**)

1.82 ± 0.18

—

Zenith luminance [mcd/m2]

SQM

0.28 ± 0.03

—

DSLR

0.24 ± 0.03

0.19 ± 0.02

  1. *Hypothetical value assuming an equal angular luminance distribution for all azimuth angles (**) inferred value assuming a constant luminance for all azimuth and zenith angles. Zenith luminance measured with DSLR and SQM are given as reference.
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