Figure 6-21.Recommended intensities for specific night activities.
The beam spread can be described in degrees or by
NEMA types (table 6-2). The beam spread is based on
the angle to either side of the aiming point where the
candlepower drops to 10 percent of its maximum
value. The lamp and floodlight NEMA type is given in
the upper left-hand corner of each isofootcandle
a vertical (V) designation. The horizontal value is
always given first.
Example: NEMA TYPEH
MOUNTING HEIGHT AND SPACING
The NEMA type should only be used as a
reference. It does not describe the shape of the light
pattern the floodlight produces or the peak
illumination level (footcandles). Symmetrical
floodlights have the same horizontal and vertical beam
spread and are classified with one NEMA number.
Asymmetrical beam spreads have a horizontal (H) and
The size of the area to be illuminated has a direct
effect on determining the number and spacing of the
poles. The suggested area that can be covered by a
single pole is four times the mounting height. That is
known as the 2X-4X rule (fig. 6-22).
Areas lighted from interior poles or other central
locations (fig. 6-22A) can be more economical, but