Equipment: Road Surfaces - Road Lighting: Fundamentals, Technology and Application - page 175

It can be seen that a lower lighting level suffices for an identical visual perfor-
mance. For example, to get the same revealing power value at 1 cd/m 2 the brighter
surface does not need 1 cd/m 2 but only approximately 0.7 cd/m 2 : an extra saving
of 30 %. Of course, the positive effect of visual performance only concerns those
objects seen against the road surface, which, as we have seen, is especially the case
for roads meant for motorized traffic.

12.7 Acquirement of Reflection Data

Here we will discuss the ways in which the reflection properties of a particular surface
may be determined. This in order to learn to which class the surface belongs and
which of the standard reflection tables should be used as a basis for the lighting
design. In this respect it is important to realize that most surfaces will show a change
in their reflection properties with wear, the change normally being greatest during
the first few months of use, after which the surface characteristics more or less
stabilize. This stabilized surface condition is, of course, the one that should be taken
for lighting-design purposes. The change in reflection properties will not be constant
over the whole road surface. Ideally, therefore, the reflection properties should be
determined for a number of different locations on the road in order that its 'average'
reflection properties may be defined. It also means that it has little practical meaning
to determine the reflection properties to a very high degree of accuracy.
There are various ways of determining the reflection properties of a given road
surface: laboratory measurements, in-situ measurements, and by a comparison of
road-surface materials.

12.7.1 Laboratory Measurements

An complete reflection table can be drawn up based on measurements performed on
a small sample of the road surface concerned. This method is both complicated and
time consuming: the sample must be cut and then transported to a suitably-equipped
lighting laboratory. The sample (or preferably samples) should be taken from a part
of the road that is representative of the whole. For new road surfaces this method is
not possible, because the road surface reflection properties are not yet stabilized.

12.7.2 In-situ Measurements

Few portable reflectometers for in-situ measurements with sufficient accuracy are
available. Normally, therefore, this method is not feasible for daily road lighting de-
sign practice. Chapter 14 will describe the working principle of some of the portable
reflectometers.