To be able to examine the quality assessment of a lighting system in a complex, we must consider various factors simultaneously:
- Visual Comfort: This means not feeling tired when in an environment. Factors such as good color rendering and uniform luminance distribution are effective in achieving visual comfort.
- Visual Performance: The ambient lighting must be sufficient to meet the needs of the human eye for perceiving objects, and at the same time, factors that cause glare must be limited.
- Visual Ambience: Visual ambience means that by suitable selection of light color and direction, objects can be perceived in three dimensions.
Illuminance level, glare, uniform luminance distribution, light color, light direction, and color clarity are considered quality indicators in lighting, which we will explain below:
Illuminance Level:
One of the most important factors for transformation in the use of artificial light is illuminance intensity. The illuminance intensity of an urban space depends on the luminous flux of the lamps, the light distribution intensity of the luminaires, the arrangement of the lighting system installation, and the reflective properties of the floor surface.
Glare:
Glare is one of the annoying factors in lighting that restricts the field of vision and causes fatigue for individuals, and should be minimized as much as possible. The use of inappropriate luminaires, improper placement of luminaires or windows, and high reflection from various surfaces are factors that cause glare. Glare exists in two forms: Direct Glare and Indirect Glare.
Direct glare is caused by the inappropriate shape of the light source and improper placement of the lighting source. The presence of a bright light source in the field of view causes discomfort (psychological glare) and reduces the quality of visual performance (physiological glare). Glare is much more important in outdoor lighting because, for example, in the case of street lighting, glare can reduce drivers’ visibility and create life-threatening hazards.
Indirect or reflected glare results from the reflection of light from polished surfaces present in the field of view, causing visual disturbance and reducing the contrast needed for seeing. Any surface at an undesirable angle or with strong contrast can produce reflected glare, which can be remedied by changing the angle or intensity of the light source, or by dulling and changing the color of the reflective surface.
Uniform Luminance Distribution:
The luminance of a surface depends on factors such as illuminance intensity, the direction in which light strikes the surface, the characteristics of the surfaces (smooth, matte, or colored), and the location from which the surface is viewed.
If there is a very small difference (to the extent that the environment appears uniform) or a significant difference between the luminance of the surroundings and the environment with which a person’s eye constantly interacts, the person becomes fatigued. In general, it is recommended that the luminance of a person’s surroundings should not be less than one-third of the work surface luminance. Also, in cases where a high luminance is required on the work surface for precise tasks, this luminance should not be more than ten times the luminance of the surroundings. A practical solution for proper luminance distribution in the environment is the use of surfaces with different reflection coefficients.
In urban space lighting, luminance is the main criterion for determining the quality of the lighting system. Therefore, in the lighting of historical buildings and outdoor areas, it is recommended that the illuminated surface has uniform luminance so that it appears consistent to the observer’s eye. Furthermore, in the design of street lighting, for security reasons, uniform localized luminance distribution is crucial for identifying obstacles and hazards.
Light Color:
In urban spaces, volumes, textures, and building facade details gain more beauty with the help of light. The light color of each place should be chosen considering its cultural and social aspects and concepts, so that in addition to its psychological and physical effects on individuals, it also influences their behaviors and emotions, as well as their spatial perception. The situation that color creates in space affects human feelings, perception, and health through the warmth and coolness of light.
Light Direction:
The ability to distinguish three-dimensional objects, structures, and surfaces is influenced by the direction of illumination, the ratio of light to shadow (chiaroscuro). The direction of light incidence can reveal the shape and texture of objects or practically leave them in ambiguity. The direction of the light source significantly affects the perception of three-dimensional objects. The ability to perceive volumes is influenced by the degree of light and shadow present on them.
