Visual Performance and Sense of Confidence - Road Lighting: Fundamentals, Technology and Application - page 281

Fig. 20.15 An after-image may occur when, after concentrating for some 20 s on the bright picture
(fixate the black dot ), one subsequently concentrates on the darker area (fixate the white dot )

Fig. 20.16 Luminance
reduction in terms of the
transition-zone luminance,
L tr ,of CIE and of different
researchers with indication of
the luminance starting point

100

L tr
(%)

30

10

CIE

3

1

Mäder and Fuchs
8000 cd/m 2

Kabayama
1500 cd/m 2

0.3

Schreuder
8000 cd/m 2

0.1

0 5 10 15 20

t (sec)

Determination of the speed with which the luminances in the transition zone can
be reduced without experiencing after-images and without losing sight of a critical
object in that zone, has been carried out by Schreuder ( 1964 ). Kabayama ( 1963 ) and
Mäder and Fuchs ( 1966 ) conducted similar investigations, but solely on the basis of
visibility criteria. In these investigations luminance values for the starting point of
the reduction varied widely. Figure 20.16 shows the results on a relative scale.
The permissible reduction is only slightly dependent on the starting luminance
value, and the relative curves are in good agreement with each other. However, since
these early investigations, experience with real tunnels has shown that when these re-
duction curves are applied in practice, a strong feeling of discomfort is experienced,