FLOODING AIMING

When a fixture is aimed at the surface at an angle other than perpendicular, the maximum lighting level will always occur behind the aiming point, or point of maximum candela. This is important to know when the fixtures are placed close to the base of a tall structure. In this case the highest lighting level will occur at the base even though the fixture is aimed at the top.

For vertical aiming, the aiming point should be two-thirds to three-fourths the distance across the area or twice the mounting height, whichever is the lowest value. Higher aiming angles will not improve utilization and uniformity. (See fig. 1-21.)

The highest light level (vertical and horizontal) a floodlight can produce at a distance from the pole occurs when the maximum intensity or candlepower is aimed to form approximately a 3, 4, 5 triangle. (See fig. 1-22.) This is useful when determining pole height for area lighting or setback for building floodlighting.

Floodlights with NEMA 6 or 7 horizontal beams will effectively light an area 45 to either side of the aiming line. In figure 1-23, the perimeter pole needs at least two floodlights to cover the area in all directions. Narrower beam floodlights require less separation to achieve uniform lighting.

Figure 1-21.\Vertical aiming.

Figure 1-22.\Maximum candlepower of illumination.

Select lighting fixtures with a beam spread greater than the area being lighted. Where 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 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 SpotR floodlight has a beam spread of 22 horizontal by 21 vertical, whereas a NEMA Type 5 has a beam spread of 77 horizontal by 77 vertical. The isofootcandle diagrams shown in

Figure 1-23.\Horizontal aiming.

Figure 1-24 compare 1,000-watt metal halide at a 50-foot mounting height and aimed 100 feet Power SpotR luminaires of NEMA Type 2 and (2 x MH) directly in front of its location. If you Type 5 when each luminaire is aimed out a are using a NEMA Type 2 distribution, the distance of twice its mounting height. approximate initial footcandle level at that point

The initial footcandle level at the aiming point would be 20; however, if you are using a NEMA ^{of different NEMA Types varies a great deal. For} Type 5 distribution, the initial footcandle level example, assume that each luminaire is mounted would be approximately 1.5.

Figure 1-24.\Isofootcandle diagrams.

By understanding the intensity of the lighting pattern, we can now appreciate the need for a range of distribution patterns.