Age Effects - Road Lighting: Fundamentals, Technology and Application - page 87

7.2 Age and Visual Performance

In Chap. 3, Sect. 3.2.1 revealing power has been used to show the influence of the
lighting parameters average road-surface luminance, L av , uniformity, U o and glare
restriction, TI, on visual performance for 30-year-old motorists (7 minute object).
The dramatic effect of age becomes clear from Fig. 7.5 where the revealing-power
curve, for good uniformity and glare restriction, of a 30-year-old person is given
together with the curves obtained for a 50 and 60-year old person. The age effects
are calculated from Adrian's model discussed in Chap. 3 (Adrian 1989 ). At 1 cd/m 2
for both the 50 and 60 years age groups the revealing power value is zero—which
advocates that motorists in these age groups should slow down.
At lower driving speeds, the safe stopping distance is shorter. From that shorter
distance a same object is seen at a larger visual angle, thus increasing visibility.
To illustrate this effect, Fig. 7.6 gives the revealing power results, again for good
uniformity and glare restriction, for an object seen under an angle of 9 minute. This
corresponds to a 20

20 cm object seen from a distance of 75 m (safe car stopping
distance at a driving speed of 80-90 km/h). At a lighting level of 1 cd/m 2 both the
age groups of 30 and 50 years get a high enough revealing power value. However,
the age group of 60 years requires a lighting level of 2 cd/m 2

×

for an only moderate

revealing power value.

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