Visual Performance and Sense of Confidence - Road Lighting: Fundamentals, Technology and Application - page 283

100

80

L tr

60

(%)

40

20

10

8

6

4

2

t (sec)

0 2 4 6 8 10 12 14 16 18 20

80 km/h
100 km/h

100 200 300 400 d (m)

d (m)

100 200 300 400 500

120 km/h 0 100 200 300 400 500 600 d (m)

Fig. 20.18 CIE luminance-reduction curve showing the maximum permissible rate of decrease in
the transition zone

have seen in the previous Section, in the beginning of this interior zone, adaptation
is not yet complete and it is therefore necessary to arrange for a level of luminance
that is fairly high compared with the level needed on an open road at night with
a static adaptation. Even in very long tunnels where adaptation gradually becomes
complete, the lighting level needs to be higher than that on an open road at night.
The reason for this is that in a tunnel there is less space to correct an error and less
space to avoid obstacles; and if an accident does occur, the consequences are likely
to be more severe. Practical experience has shown that levels of 2 to 10 cd/m 2 are to
be recommended for the interior zone, the lower levels being acceptable for tunnels
with low traffic density and driving speed.

20.5 Exit Zone

The adaptation state of a driver approaching a tunnel exit gradually increases because
the bright exit gradually increases in size during the approach. Since adaptation from