Figure 6-13.—Pavement brightness.utilization for any specific situation is obtained fromthis curve. The utilization curve will determine theamount of light that actually strikes the roadwaysurface. This percentage of light has an impact on thespacing distance of the luminaries.elevation. Thus, at any point on the diagram (orroadway), we know the magnitude and direction of theillumination with respect to nearby points. To makethis data more universal, you are given both the tophorizontal and left vertical axes in terms of mounting-height ratios.Isofootcandle CurveIt is sometimes convenient for you to replot theThe isofootcandle diagram (fig. 6-14B) shows theisofootcandle data to the same scale as that used on adistribution of illumination on the road surface in thedrawing containing a lighting layout. Byvicinity of the luminaire.superimposing this diagram, you can study thedistribution of light. Under the unity correction factorThe lines on this diagram connect all points havingin the mounting-height table (fig. 6-14B), one can findequal illumination, much as the contour lines on athe mounting height for which the data are calculated.topographical map indicate all points having the sameThe numbers beside each line represent the initial6-13