Visual Performance for Motorists - Road Lighting: Fundamentals, Technology and Application - page 23

RP = 100 % RP = 50 %

Fig. 3.11 Left : objects with a reflectance factor distribution typical for pedestrian clothing. Right :
those objects that remain visible under relatively poor road-lighting conditions (revealing power of
50 %)

Fig. 3.12 Revealing power
(RP) of cloth and objects at
the darkest location on the
road as a function of the
average road-surface
luminance (L av ) for U o = 0.4
and TI = 10 %. Thin broken
lines: contribution of objects
seen in positive contrast.
Visual angel 7 min, age 30
years

cloth

100

30 yrs U o = 0.4 TI = 10 % 7 min

RP (%)

objects

75

50

objects

pos. contrast

25

cloth
pos. contrast

0
0.1

0.2 0.5 2 5

1 10

L av (cd/m 2 )

That more objects become visible in positive contrast (see broken lines in Fig. 3.12 )
is not enough to compensate for this loss.
The influence that uniformity and glare restriction have on visual performance
becomes evident from Fig. 3.13 where, for the cloth targets, the revealing power
values are given for three different combinations of uniformity and glare restriction:

•U o = 0.40 and TI = 10 % representative for “good” road lighting

•U o = 0.25 and TI = 10 % representative for bad overall uniformity

•U o = 0.40 and TI = 30 % representative for too much glare.

When the uniformity decreases from U o = 0.40 to only 0.25, the revealing power

will, at a lighting level of 1 cd/m 2 , fall back from 80 % to only a poor 43 %. That