Candela Plots
Candela plots are graphical representations of candela tabulation data (figure 2). Outdoor lighting produces unique light patterns which are difficult to represent in a flat two-dimensional plane. Therefore, to create distribution plots that illustrate luminaire performance, curves are plotted with a three-dimensional dynamic. An example, based on the candela tabulation data above, is presented in the charts shown in Figure 4.

Using the tabulated maximum candela value, which in this example is 8595, two planes are identified: a lateral angle of 71°, and a vertical angle of 66°. The vertical angle is used to create a cone, with its slope equal to the vertical angle of maximum candela (66°). On this cone, all lateral candela distribution values from the tabulated data row at 66° are plotted. The result is shown on the right side of the cone chart. The two-dimensional view looks down at the top of the constructed cone.

Figure 4: Maximum Plane and Cone Plots of Candela

The second value, the lateral angle of 71°, is used to construct a vertical plane off the lateral baseline. The result is shown on the left side of the cone chart. On this surface, all vertical candela distribution values from the tabulated data column at 71° are plotted. For purposes of presenting the plot, the vertical plane is flattened, or laid back 90°, to show it in the same plane as the right side plot.

The chart is also shown in a perspective view, to help visualize the relationship between the two plotted curves. The combination of the two curves represents luminaire performance in three dimensions.