Visual Performance, Comfort and Pleasantness for Pedestrians, Cyclists and Residents - Road Lighting: Fundamentals, Technology and Application - page 61

Fig. 5.2 The concept
of vertical versus
semi-cylindrical illuminance

E

proper identification of faces, the lighting at face height at all locations in the street
should be sufficient. Sometimes the vertical illuminance at face height is used as
the basic lighting parameter for providing this information. However, the semi-
cylindrical illuminance at face height is a somewhat better basic parameter for this
purpose This is because the human face is not simply a flat vertical plane: light
incident on the sides of the face contributes to its visibility (Fig. 5.2 ).
Figure 5.3 shows the results of identification tests of faces under road-lighting
conditions (Van Bommel and Caminada 1982 ). As a basis for the lighting-level re-
quirement, an identification distance of 4 m is sometimes proposed (Van Bommel
and Caminada 1982 ; CIE 2000 ). At this distance an alert person can still take an
evasive or defensive action. From Fig. 5.3 it follows that a semi-cylindrical illumi-
nance value of slightly less than 1 lx, fulfils this requirement. The anthropologist
Hall ( 1969 / 1990 ) recognized, on the basis of worldwide research of the human use
of space, that human beings like to keep a certain distance from each other, the actual
distance being dependent on the type of social contact.
Hall defines four different so-called “proximity zones” (Fig. 5.4 ):

• the intimate zone,

• the personal zone (family members),

• the social-consultative zone (business contacts),

• and finally the public zone (people who do not know each other).

The public zone begins at a distance of some 4 m. Urban lighting that enables the
identification of persons at this distance thus promotes a “natural” feeling of comfort