Civil Engineering Reference
In-Depth Information
Fig. 2.3
The terms horizontal
illuminance (E
hor
),
hemispherical illuminance
(E
hemisphere
), vertical
illuminance (E
vert
), façade
illuminance (E
facade
) and
semi-cylindrical illuminance
(E
semi-cyl
) refer to the
illuminances on an (infinitely
small) body of the shape
illustrated
E
semi-cyl
E
vert
E
facade
E
hemisphere
E
hor
2.2.2
Vertical and Semi-cylindrical Illuminance
For security reasons, it is important to be able to identify one another on meeting in the
street. It is for this reason that the vertical illuminance at face height is sometimes used
as the basic lighting parameter. It has been shown, however, that the semi-cylindrical
illuminance at face height is an even better basic parameter for this purpose (see again
Fig.
2.3
). This is, as will be discussed in more detail in Chap. 5, because the human
face is not flat, and light incident on the sides of the face contributes to its visibility. It
is the vertical illuminances on the facades bordering the street that actually determine
how well these facades can be seen. Appendix A gives the calculation formulas for
vertical and semi-cylindrical illuminance.
Reference
Van Bommel WJM, De Boer JB (1980) Road lighting. Kluwer Technische Boeken, Deventer
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