Aplicación del procedimiento al Caso de Estudio

The amount of light required for a night-time installation depends on two factors: the visual tasks involved, and the average luminance of the surroundings. Table 12.2 gives typical recommended illuminances for a range of situations. The principles of display lighting described in Chapter 11 apply to exterior lighting design: if a building

Table 12.1 Functional checklist for exterior lighting Safety

Does the lighting enhance visibility of hazards, such as steps, kerbs, water edges and steep gradients?

Security

Are there areas that need lighting for prevention of crime or to give a sense of security to pedestrians or to people in the buildings?

Is lighting for CCTV cameras required?

Guidance and orientation

Does the lighting of pathways and drives indicate the route over a distance?

Are elements such as entrances, seats and telephone kiosks easily visible?

Glare, distraction and light pollution Is the lighting glaring to pedestrians or drivers?

Does it confuse visibility of traffic signs?

Does it shine into habitable rooms?

Is light shining into the sky reduced to a minimum?

Luminances

Are the final luminances appropriate to the general area?

Does the design take into account any existing illumination of facades or streets, or internal lighting of windows?

Colour

Is the colour rendering of light sources related to the surface materials?

Does the lamp colour appearance give an appropriate sense of warmth or coolness?

Does the choice of lamps take into account any existing lighting?

Installation

Are the luminaire positions easily served by a power supply?

Can they be maintained easily?

Are they protected from vandalism and accidental damage?

Is planning permission necessary, or consent from adjacent owners?

Energy conservation Are high-efficacy lamps used?

Do the luminaires have a high light output efficiency?

Do they illuminate only the areas required?

Are they switched to avoid unnecessary use, with automatic controls where appropriate?

is to be enhanced with floodlighting, or if an urban feature is to be emphasized, what is impor-tant is the brightness contrast between the subject and its surroundings. Figure 12.3 illustrates

Figure 12.3 Typical average ambient luminance due to night-time lighting.

how ambient night-time luminance increases with closeness to a city centre. In open countryside no electric lighting may be visible; as a town is approached, highway lighting begins to give a general illumination; in a busy city street there are many sources—road and vehicle lighting, shop windows and signs, building floodlighting. The datum for design is the average brightness of the immediate area.

Table 12.2 Typical recommended exterior night-time illuminances

Purpose LuxOn which surface?

Driveways to buildings, secondary pathways 5 Horizontal with at least 50% this value on vertical

Main paths, outdoor car parks 10 Horizontal with at least 50% this value on vertical

116 The design of lighting

Security areas around buildings, main shopping streets

20 Vertical at 1.5 m above ground Steps, footbridges and similar hazardous zones,

entrance areas to buildings, recreational football pitches

50 Horizontal (vertical surfaces of steps should be differentiated) Covered pedestrian areas, arcades 75 Vertical at 1.5 m above ground Illuminated signs in low brightness districts 100 Vertical

Bus stops, coach loading areas, recreational tennis courts

150 Horizontal Illuminated signs in high-brightness districts 500 Vertical

The illuminance ratios given for display lighting in Table 11.1 give a guide to the luminance dif-ferences that may be required between a surface and its surroundings. When an object or a surface is about twice as bright as the adjacent area the difference is just noticeable; a luminance ratio of 5:1 appears significantly different. When the ratio is more than 10:1 the difference in apparent brightness is emphatic—the lighting on a feature emphasized to this extent might be called ‘dramatic’. Where several levels of brightness are planned within a design, equal steps in apparent brightness should be taken to follow an approximately logarithmic increase in

Figure 12.4 Luminance variation across a floodlit building.

luminances: that is, a sequence of relative values such as 1:3:9:27. Figure 12.4 shows the great range of luminance that typically occurs on a floodlit building.

Most external building surfaces are sufficiently matt to be treated as diffuse reflectors.

Luminance then is related only to illuminance and reflectance (described in Chapter 1). In this way luminances from electric lighting can be compared with existing values of ambient luminance. Exterior lighting that is inappropriately bright for its surroundings may be considered a type of light trespass and a cause of neighbourhood dissatisfaction.

Many tasks do not depend on good colour rendering; it is predominantly the level of illuminance and the three-dimensional modelling that determine visibility, so lamps for exterior lighting may often have poorer colour rendering than normally required within buildings. But in city squares and shopping malls where people, the things they wear and carry, and the natural materials of the ground and the buildings, form many of the subjects of view, good colour rendering is an indicator of the quality of an installation. High-pressure sodium lamps are commonly used satisfactorily, particularly those with de luxe colour performance. Fine materials on a historic building may best be displayed naturally, using a white light with good colour rendering. But many inherent material colours can be empha-sized—such as the use of red light on brickwork—and neutral surfaces such as concrete can accept a richness of colour that gives interest and complexity far different from their daytime expression. The creative use of colour is at the heart of good nighttime lighting.

Very accurate colour rendering is required for colour TV, particularly of sports fields;

here metal halide lamps are the usual solution.