Facades
Correct lighting of a façade is the essential finishing touch to enhance the aesthetical value of a building. There are a number of rules, which must be observed in this kind of lighting.
Firstly it is important that there is harmony between the colour of the light cast and the material, which composes the façade or monument. In order for the night perception of the illuminated surface to be similar to that in the day, the colour tone should be homogenous with the dominant colour of the façade or monument. Thus light with a colour tone between 2000K and 3000K should be used for red bricks, calcareous stones, plasters or other material and tints of a warm colour tone as red, pink and ochre. On the other hand light with a colour tone of between 4000K and 6000K should be used for facades made up of concrete, marble, granite or other material of a cold colour tone as white, grey, green or blue.
For porous material, it is preferable to use warm lights as this highlights its coarseness. On the other hand, having a light that is too bright on marble could result in the setting being too flat.
Metal halide and fluorescent lamps are normally used for façade and monument lighting. Metal halide lamps represent a good balance between luminous radiation, lamp life and luminous efficiency. Fluorescent lamps present good energy saving and give the possibility to choose between different colour tones (between 3000 and 6000K). Xenon lamps are also used for facades. These give out a light emission of 2600K, which is particularly suitable for lighting historical buildings. Xenon lamps is very advantageous in terms of energy saving, lamp life and quality of light. These lamps do not emit UV rays.
Wide beam projectors, that is projectors with a light cone greater than 60°, are used when the light fitting is to be placed relatively close to the surfaces which need to be illuminated. Medium beam projectors, being projectors with a light cone between 30° and 60°, are used when the surfaces are 20m to 40m from the light fittings. Medium beam projectors allow better control of glare. Narrow beam projectors, meaning projectors with a light cone less than 30°, are used when surfaces are more than 40 metres from the light fitting. Narrow beam projectors are used to highlight architectural details while minimising glare. To avoid excessive inclination of the light fittings as well as light dispersion, asymmetrical optics may be used. Asymmetric optics emit their maximum luminous intensity at 45°. These light fittings allow large spaces to be illuminated while preventing the production of stray light, which results in glare.
Vertical unevenness in lighting can be obtained by moving projectorss closer to a façade than they would be positioned in the case where a uniform lighting is required. Vertical unevenness is mainly used to light steps. Horizontal unevenness is obtained by increasing the space between the light fittings more than if uniform lighting on the façade is required. Horizontal unevenness is mainly used to enhance the rhythms of architectural elements such as facades with columns. Diffused lighting, that is when the light fitting is placed very close to the surface that needs to be illuminated, is used to highlight the architectural details as decorations.
If one wants to highlight the architectural elements that develop horizontally, as cornices, the light projectors are normally positioned in front of the façade, at an angle that guarantees a high angle of incidence. If the elements that need to be illuminated develop vertically, as columns, the projectors are usually positioned laterally.
