Figure 6-11.—Light distribution patterns for roadway lighting.

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 practice. 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 fixture. 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. 6-11