Figure 6-19. - Isofootcandle curve.
Figure 6-20. - Roadway perspective view.
For lighting extended vertical surfaces, such as smoke stacks or towers, mount floodlights so distance between floodlights or groups does not exceed twice the distance from the floodlight to the illuminated surface.
Use a smaller number of large floodlights instead of a larger number of smaller floodlights.
The National Electrical Manufacturer's Association (NEMA) has classified floodlighting luminaries into four classes according to construction:
1. Class HD (Heavy Duty) - Enclosed with an outer housing into which is placed a separate and removable reflector, or an enclosure in which a separate housing is placed over the reflector
2. Class GP (General Purpose) - Enclosed with a one-piece housing with the inner surface serving as a reflector and the outer surface being exposed to the elements
3. Class O (Open) - One-piece housing without cover glass
4. Class OI - Same as Class O except with an auxiliary inner reflector to modify the beam
The suffix letter "B" should be added to the above class designations to indicate when an integral ballast is required.
Example: A heavy-duty floodlight with an integral ballast would be designated as a Class HDB floodlight.Continue Reading