Civil Engineering Reference
In-Depth Information
Fig. 3.14
Revealing power
values at all grid points
between a luminaire span.
Black dots indicate the
lengthwise observer positions
for the different rows of grid
points. Values below 90 % are
shown in a darker shade
9
8
93
91
95
87
69
96
92
85
Fig. 3.15
Area ratio as a
function of average road
surface luminance L
av
. Visual
angle 7 min, field factor 3 and
age 28 years. Two-lane road
with opposite and staggered
arrangements and a light (CIE
R1) and darker (CIE R3) road
surface. Mounting height
10 m. (Based on Narisada and
Karasawa
2001
)
Opposite, R1
100
Area
Ratio
(%)
Opposite, R3
75
Staggered, R3
50
25
0.5
1
1.5
2
L
av
(cd/m
2
)
luminance. Results are given for luminaire arrangements on both sides of a two lane
road in an opposite and staggered arrangement and for two different types of road
surface (a diffuse light one, R1, and a darker somewhat more glossy one, R3).
As with the revealing-power curves shown in the previous section, a pronounced
increase in visual performance (area ratio) is obtained when the average road sur-
face luminance increases from 0.5 cd/m
2
to 1 cd/m
2
. Here too, the curves level off
between 1.5 cd/m
2
and 2 cd/m
2
. That the staggered arrangement results in lower
visual performance is a consequence of the lower uniformity that accompanies such
an arrangement. It is important to note that the lighter road surface R1 results in
considerably higher visual performance than that provided by the darker surface R3.
This is because for the same average road surface luminance level the ratio of vertical
illuminance to road surface luminance is smaller with lighter road surfaces, so that
silhouette vision is improved. Section 12.6 will elaborate on this effect.
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