Equipment: Road Surfaces - Road Lighting: Fundamentals, Technology and Application - page 170

Table 12.2 R, C and N-class limits and class-standards
Class name Class limits Class standard Standard Q 0

RI S1 < 0.42 R1 0.10

RII 0.42 ≤ S1 < 0.85 R2 0.07

RIII 0.85 ≤ S1 < 1.35 R3 0.07

RIV 1.35 ≤ S1 R4 0.08

CI S1 < 0.40 C1 0.10

CII 0.40 ≤ S1 C2 0.07

NI S1 < 0.28 N1 0.10

NII 0.28 ≤ S1 < 0.60 N2 0.07

NIII 0.60 ≤ S1 < 1.30 N3 0.07

NIV 1.30 ≤ S1 N4 0.08

road surfaces typically occuring in Scandinavian countries where artificial surface
brighteners are often employed, which makes surfaces very diffuse. All good lighting-
calculation software packages have the R, the C and the N-standard reflection tables
stored in their database.
The R and C-classes as well as the N classes and their standards, are based on the
set of road surfaces measured in the 1960s and 1970s of last century. As has been
mentioned before, actual measurements recently carried out on road surfaces show
that the road surfaces of last century are no longer representative enough for today's
practice. The technical committee of CIE, already referred to, that is working on the
subject of refection properties of road surfaces, will also try to define class limits
and standard tables based on road surfaces that are in use today.

12.4 Influence of Spectrum of Light

The reflection of a road surface, like most surfaces, is not constant over the whole
wavelength area: in other words, road surfaces are not completely achromatic. Ekrias
et al. ( 2009 ) measured the spectral reflectance of eight different stone-mastic asphalt
surfaces, while Adrian and Jobanputra ( 2005 ) measured a concrete surface. Their
results are shown in Fig. 12.7 on a relative scale where the reflectance at 400 nm is
put at 100 %.
As can be seen, for all surfaces the reflectance is higher for longer wavelengths.
Consequently, light sources that emit more light at longer wavelengths (warmer
tinted light) reflect more light from the road surface and thus are more efficient in
creating road-surface luminance. From Fig. 12.7 the effect seems to be considerable.
However, one has to bear in mind that the eye sensitivity is low at long wavelengths.
For the asphalt road surface, having the largest spectral effect (the bold drawn curve
in Fig. 12.7 ), the resulting road surface luminance has been calculated for different