Figure 6-25.Horizontal aiming.
Select lighting fixtures with a beam spread greater
than the area being lighted. When several units are
required, good lighting overlap occurs when the edge
of the beam of one fixture coincides with the aiming
point of the adjacent fixture.
By examining the shape (beam spread) of the
lighting pattern emitted by the fixture, you can begin
the process of selecting the NEMA type of floodlight
best suited for the application.
Horizontal and vertical lumen distribution is stated
on each photometric test. Generally, the more
concentrated the luminous intensity (candela), the
tighter the beam spread; for instance, the NEMA Type
2 Power Spot® floodlight has a beam spread of 22-
degrees horizontal by 21-degrees vertical; whereas, a
NEMA Type 5 has a beam spread of 77-degrees
horizontal by 77-degrees vertical. The isofootcandle
diagrams shown in figure 6-26 compare 1,000-watt
metal halide Power Spot® luminaries of NEMA Type
2 and Type 5 when each luminaire is aimed out a
distance of twice its mounting height.
The initial footcandle level at the aiming point of
different NEMA types varies a great deal; for example,
assume that each luminaire is mounted at a 50-foot
mounting height and aimed 100 feet (2 x MH) directly
in front of its location. If you are using a NEMA Type 2
distribution, the approximate initial footcandle level at
that point would be 20; however, if you are using a
NEMA Type 5 distribution, the initial footcandle level
would be approximately 1.5.
By understanding the intensity of the lighting
pattern, you can now appreciate the need for a range of
The performance specifications of each model,
type, and size of luminaire are provided with the
fixture or obtained from the manufacturers ordering
catalog. A working knowledge of this information will
assist you in selecting and installing the correct
floodlight to accomplish the job. Figure 6-27 shows a
sample of manufacturers literature for a 250- to 1,000-
watt light fixture.