Figure 6-17. - Utilization curve
Figure 6-18. - Streetlight layout.
The minimum point footcandies are
fc min = (0.03) (50) (0.70) (0.56) = 0.58
Therefore, the average-to-minimum ratio of uniformity would be 2
fc/0.58fc = 3.40
A uniformity ratio of 3.40 meets the ANSI/IES recommended roadway illumination levels (table 6-1) for a major, commercial roadway.
Streetlighting systems usually give lighting intensity from .01 to 0.5 footcandle; however, this value is too low for any night activity requiring good visibility. Figure 6-21 gives recommended illumination intensities for specific night activities. The following suggestions should be followed to improve the efficiency of floodlighting systems:
Select floodlight locations so beams strike the surface to be illuminated as nearly perpendicular as possible.
When lighting irregular surfaces, use two or more floodlights to reduce sharp shadows caused by surface contour.
For lighting extended horizontal surfaces, such as work areas, mount floodlights high enough to minimize glare.Continue Reading