Each second image in a row shows luminance coded by colours (each colour corresponds to another power of ten, scale is logarithmic; mean red is 1 cd/m2, mean green is 10 cd/m2)
Each third image has a grid overlay. Average luminance of each tile is written at its bottom (in cd/m2). (The middle number in each tile is a median value of green pixels.) Each fourth image has the same grid overlaid on colour-coded luminances.
Logarithmic luminance scale (the unit is candela per square meter)
– intensities of snow illuminance in lux would be obtained by
multiplying the numeric value of luminance by 3.6. For
asphalt,
such a coefficient is between 20 and 40
(or much less, for specular reflections of distant lamps)
Further three images in a row code similarly a ``circadian'' (melatonin production affecting, non-imaging visual subsystem) luminance, from the B pixels of the image. (See a poster from Graz conference, g_camer.pdf for its definiton.) In fact, eye sensitivity is far from being uniform for this radiation, maxima being in upper outer quadrant as seen by each eye (see Melatonin Suppression by Light in Humans Is Maximal When the Nasal Part of the Retina Is Illuminated -- Visser et al. 14 (2): 116 -- Journal of Biological Rhythms). Real scenes photographed with a fish eye lens should take it into account in the future.
Westminster bridge over Thames, Parliament and Big Ben are shown. Glare
from the lamps on the bridge becomes prominent already.
A pleasant court (The Temple) illuminated by gas lamps
(glaring, but not too strong).
A beam from a skybeamer behind.
Sky luminance from 0.10 cd/m2 to 0.05 cd/m2,
terrain about 0.02 cd/m2.
Sky with Vega and Deneb within the top of the Northern Cross.
Towards city centre, sky luminance is about 24 mcd/m2.
Sky with Andromeda, Great Square and Aries stars, away from city centre.
Sky luminance about 20 mcd/m2
Sky with Perseus, two Andromeda and Aries stars and some high clouds;
airplane at upper right.
Clear sky luminance about 18 mcd/m2,
clouds have 22 mcd/m2