A New Calculation Method for Roadway Lighting Design
The current street lighting standards use the horizontal illuminance or luminance measures at the pavement level as design targets. However, a driver not only needs to see the pavement, but also obstacles on the pavements that have different vertical heights relative to the ground. Furthermore, while the illuminance measures are easy to calculate, human visibility depends on different measures one of which is the contrast. Many recent work have criticized the current standards and encourage to propose an alternative to it. This study presents a new calculation procedure for street lighting design that is based on the contrast of obstacles along the road. It also includes a critical investigation of how this could change street lighting calculations by introducing four contrast index for street lighting design. The current study uses computer simulation created for a two-lane street. Obstacles are distributed along the lateral and longitudinal direction of the road. Vectors that initiates from the driver’s eye to each targets are then used to specify the location of the background of this target. Then, the luminance for targets and their background is computed. After that, a contrast value is calculated for each target. The simulation program is used to test different street lighting design variables such as pole spacing, car headlights, wattage and pole heights. The findings suggest that the contrast based approach to street lighting design have merit and could be the basis for street lighting calculation in the future. Furthermore, while targets less than 1.0m high usually have negative contrast, targets at 1.0m and above usually have positive contrast. The influence of the different street lighting design variables are also studied. The results revealed that turning car headlights on makes the contrast more positive and it is found to have the greatest impact on contrast for targets less than 1.0m. Two other variable are the pole spacing and the luminaire wattage. A critical investigation of their results shows that while increasing the pole spacing affects the contrast by making it more negative, changing wattage is found to have the minimal impact on the contrast. Nevertheless, higher pole height is to produce more uniform contrast distribution of targets. Four contrast index are viii proposed in this thesis. A critical examination of the influence of the different street lighting variables shows that the useful contrast index has the largest response to changing these variables and is concluded to be the most suitable index to be used for the street lighting design. It is critical to note that the results of this thesis are limited to the street studied here.