Figure 6-11.Light distribution patterns for roadway lighting.
line of vision and the less glare it creates. Greater
mounting heights may often be preferable, but
heights less than 20 feet cannot be considered good
You must be somewhat familiar with the
terminology relating to how fixtures are located
down a roadway. Figure 6-12 shows these
relationships graphically. The following
information will be useful when determining the
most appropriate mounting arrangements:
The transverse direction is defined as back
and forth across the width of the road, and the
longitudinal direction is defined as up and down the
length of the road.
Modern roadway fixtures are designed to be
mounted in the vicinity of one of the curbs of the road.
The overhang is defined as the dimension between the
curb behind the fixture and a point directly beneath the
A luminaire overhang should not exceed 25
percent of the mounting height.
No attempt should be made to light a roadway
that is more than twice the width of the fixture-
mounting height. A roadway luminaire produces a
beam in both longitudinal directions and is limited in its
ability to light across the street.
There are three ways that a luminaire may be
positioned longitudinally down the roadway (fig. 6-12).
Note that the spacing is always the dimension from one
fixture to the next down the street regardless of which
side of the street the fixture is located.