## 5 Results
### Urban Lighting Assessment  
The European standard EN 13201-3 [77] gives rules on the points where lighting measurements should be taken. Since the purpose of survey was not the measurement of the photometric quality of the lighting installations, during the data collection the grids mandated by the European standard were not used. Points located in the shade of objects (i.e., trees) that should be avoided according to the standards were, in fact, preferred measurement locations because the step passage from dark shadow to shiny lighting can affect driving performance.  
More than 2000 points distributed along almost 6.5 km were collected in the first campaign. Half of them, reported in Figure 16a, were below 32 lx and more than 52% of the points were below 50 lx, which are the light levels of public areas with dark surroundings according to the NOAO (National  
Figure 15: Pictures of critical areas (**a**–**g**) where building and street degradation, lack of lighting and perceived unsecurity in the neighborhood were detected and in which the proposed approach was tested.  
Optical Astronomy Observatory), national center for ground-based night-time astronomy in the United States [78]. Moreover, it is worth noting that 12.5% of the points are above 500 lx and three of them exceed 2500 lx. These points where recorded under the direct light of lighting systems of private parking lot thus they are not significant in the number of records and they are not describing specific areas with high illuminance level but points of discontinuity in the average distribution. Thus, such values can be disregarded in the following analysis.  
A further parameter that could be added in the lighting evaluation could be the uniformity ratio given by the average illuminance and the minimum illuminance (E\({}_{\text{av}}\)/E\({}_{\text{min}}\)) that has defined values ranging from 3 (for expressway to 6 for local roads) and it is a crucial value for visual comfort and adaptability in the scotopic vision of the human eye. The problems that could be related to the luminance values are:  
1. The illuminance must be sufficiently high in relation to the dimensions of the object, to the contrasts, to the time of perception and to the age of the subject;
2. The luminance of the area immediately adjacent to the visual task must not be higher than the visual task itself;
3. The contrast between the immediate background of the visual task and the environment must not be accepted and the transition should be gradual;
4. The most appropriate solutions have been taken to avoid glare.  
Figure 16: (**a**) Histogram of the distribution of lux level of the measurement points; (**b**) classification of the detected illuminance according to NOAO thresholds.  
It is useful to remember that illuminance describes the measurement of the amount of light falling onto and illuminating a given surface area. Illuminance is also correlated with how humans perceive the brightness of an illuminated area.  
As a result, most people use the terms illuminance and brightness interchangeably; however, this can lead to misunderstanding, as brightness is also used to define luminance. Illuminance refers to a specific kind of light measurement, while brightness refers to the visual perceptions and physiological sensations of light.  
Luminance describes the measurement of the amount of light emitting, passing through or reflected from a particular surface from a solid angle. It also designates how much luminous power can be perceived by the human eye. This means that luminance indicates the brightness of light emitted or reflected from a surface (Figure 17).