Civil Engineering Reference
In-Depth Information
Fig. 8.1
Principle of
surround ratio (SR) and edge
illuminance ratio (EIR). For
illustrative reasons, the
right-hand side only is shown
E
road
E
surround
separate values must satisfy this requirement. In EIR the width of the strips is not
the standard 5 m but is equal to the width of one driving lane.
E
surround
(
right
)
E
road
(
right
)
EIR
right
=
E
surround
(
lef t
)
E
road
(
lef t
)
EIR
left
=
8.1.4
Glare Restriction
As we have seen, glare can take either of two forms: disability glare or discomfort
glare. In most standards and recommendations for road lighting only a requirement
for the limitation of disability glare is given. It is considered that with good restriction
of disability glare, discomfort glare will usually be acceptable as well. As has been
shown in Sect. 3.1.3.1, the final disability effect is dependent on the combination
of equivalent veiling luminance and average road-surface luminance. The overall
measure for the degree of disability glare, called threshold increment (TI, in per
cent) is given by the relationship:
L
veil
L
TI
=
65
∗
0
.
8
av
8.1.5
Summary
Table
8.1
lists the lighting quality parameters for road lighting for motorized traffic.
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