Illumination, Urban

Urban illumination can be subdivided into functional illumination and architectural or decorative illumination. The main purpose of functional illumination is to increase the safety of vehicular and pedestrian traffic. It is known that, other conditions being equal, there are 30 percent fewer traffic accidents on well-lighted streets than on unlighted streets. Quantitative and qualitative parameters of functional lighting installations are regulated by appropriate standards and rules. The illuminance of highways and streets must provide a certain value of average brightness on a dry road surface. This value depends on the traffic density (see Table 1).

Qualitative parameters of illumination, such as effects of glare and the permissible nonuniformity of brightness distribution on the road surface, are also standardized. The proper choice of layout of the lighting installation greatly affects the quality of illumination. The one-sided lighting layout is used for streets with a pavement width up to 12 m, the axial layout for widths up to 18 m, and the two-sided layout for widths up to 48 m. The ratio of the distance between streetlights (the interval) to the height of the lamppost must not exceed 4–5. The effects of glare of functional lighting installations are characterized by the glare rating. Functional illumination also includes illuminated traffic signs, which help to orient motorists and pedestrians.

Architectural or decorative illumination of cities is achieved in various ways, for example, (1) by floodlighting facades of buildings, monuments, fountains, trees and shrubs, flags, and posters, (2) by outlining a building with fluorescent or incandescent lamps, (3) by revealing the tectonics of a building with the aid of interior lighting visible from within through glass surfaces, (4) by lighting of selected parts of buildings using luminescent details, or (5) by setting up illuminated advertisements, slogans, and diagrams.

Average illuminance for facades of buildings and for monuments is determined, taking into account the reflecting characteristics of the materials of the structures and the brightness of the background against which the structures are viewed. For a low brightness of the background (≤ 1 candela/m²), the average illuminance of light-colored buildings and structures should be at least 20–30 lux, and that of dark-colored buildings at least 100–200 lux. The average illuminance of store windows is determined by the kind of street or square in which the store is located and depends on the reflecting properties of the goods that are being displayed (whether they are light-colored or dark-colored goods). For major streets or squares, the average level of illuminance of shopwindows should be at least 500 lux.

In many capitalist countries, the type of illumination for city streets sometimes assumes a one-sided, advertisement-oriented character. In contrast, in the USSR the design of architectural or decorative illumination of cities and the design of functional lighting are treated as components of the unified artistic and illumination planning of a city.