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Pt.5: The Floodlighting Of Buildings Electric Lighting Floodlighting a building or monument requires special techniques to produce an impressive result. In this chapter, we look at the various tricks employed and the lamps used for flood­lighting. By JULIAN EDGAR Buildings are usually floodlit so that their appearance can be aesthetically appreciated at night. Floodlighting is quite different to other specific forms of illumination (eg, for roads), which means that the criteria employed for floodlighting are also quite different. Floodlighting is not used to simply light every surface of a building even­ ly but instead to emphasise certain ar­ 4  Silicon Chip chitectural characteristics. A designer who created a floodlighting system that gave a natural stone building a strong green colour cast and made it look bland and boring wouldn’t be classed as very suc­cessful! Lamp types A wide variety of lamps can be used for floodlighting, with the most appropriate lamp type depending on the actual applica­tion. Incandescent lamps that are fitted with a built-in reflec­ tor (eg, PAR lamps) can be used for temporary installations where only small areas need be illuminated for short periods. However, the poor luminous efficacy of incandescent lamps means that they are not an ideal light source for long hours of use. Tungsten halogen lamps have higher efficacies than ordinary tung­ sten lamps and their availability in compact shapes and with built-in reflectors allows them to be used in small luminaires. Both tungsten and tungsten halogen lamps are easily dimmed although, of course, the lat­ ter’s lifespan suffers with dimming. However, the excellent colour ren­ Fig.1: a symmetrical floodlight spreads its beam equally in all directions from the central longitudinal axis – see Fig.3 Fig.3: the light distribution for a symmetrical floodlight. Here, the horizontal and vertical patterns are the same, so only one line is shown. dering of both types of lamps pro­ vides significant advantages in some situations. Fluorescent lamps have some limited floodlighting applica­ tions, where they can be used to illuminate linear features such as low walls or parapets. By contrast, high pressure mercury lamps are used for both gen­ eral floodlighting and for highlighting certain features. They are especially suitable where their ‘cool’ light can be used to accentuate blue or green objects. Metal halide lamps have a higher efficacy than high pres­sure mercury lamps and also give better colour rendering. Sodium lamps in high pressure form can be used to give a warm colour ap­pearance to brown, red or yellow objects. By contrast, low pres­ sure sodium lamps, with Fig.2: a bi-symmetrical floodlight has different beam spreads on each axis, but each spread is symmetrical either side of a cen­tral plane – see Fig 4. Fig.4: the pattern of light distribution for a bi-symmetrical floodlight. In this case, the horizontal spread is broader than the vertical spread. Fig.5: an asymmetric floodlight can sharply attenuate the beam in certain directions, as shown by the solid line on this graph. Fig.6: an asymmetric floodlight has different beam spreads along each axis and can sharply attenuate the light in one or more directions – see Fig.5. March 1998  5 Fig.7: the Philips building in Eindhoven has been very carefully floodlit. Note the different colour temperature lamps employed at both the extreme right and left of the photo, and the fountain in the foreground which has been brightly lit. Fig.8: the building can be broken up into its architectural components, each of which is illuminated differently: (A) low, wide, flat vertical surfaces (facades); (B) tall, narrow vertical surfaces (columns); (C) specific architectural features (accents). their monochromatic yellow spectral output, are suitable only when you want everything to appear yellow! By far, the most commonly used lamps in floodlights are the metal hal­ ide and high pressure sodium types. Luminaire types Fig.9: when illuminating facades, medium beam projectors should be placed at a distance (d) that’s one quarter the height of the building (h). 6  Silicon Chip Floodlights are classified on the basis of their general pattern of light distribution. They fall into three basic groups: (1) rotationally symmetrical; (2) bi-symmetrical; and (3) asym­ metrical. A rotationally symmetrical beam spread is produced by a floodlight that has a round face, as shown in Fig.1. This type of floodlight produces the same angle of spread in both the horizon­tal and vertical planes (and at all other angles in between). Fig.3 shows the photometric out­ line for a version that has a medium width beam. On this diagram, ‘y1-y2’ is represented by the dotted line and shows the vertical spread of light, while ‘x1-x2’ (solid line) shows the horizontal spread. As it is a symmet­ rical floodlight, the spreads are the same and so just a single (solid) line is shown. A bi-symmetrical floodlight (Fig.2) Fig.10: the Philips Atria SVF100 is suitable for the illumination of columns. It has a beam spread of only 12 degrees and uses a high pressure sodium lamp with a maximum power rating of 100 watts. has a rectangular face. In this case, the width of the beam differs between the vertical and the horizontal planes (Fig.4). Finally, an asymmetric floodlight is one that typically has a wide beam in one plane but throws the light much further in one direction than the other in the other plane. It is easier to see this on the photometric diagram than it is to describe it – see Fig.5. A typ­ ical asymmetric floodlight is shown in Fig.6. Architectural considerations Buildings can be broken down into a number of different elements which require different floodlighting techniques or equipment. Fig.7 shows the Philips building in Eindhoven at dusk, while Fig.8 identifies the different architectural elements that are individually illuminated. Facades are best lit by using high pressure sodium or metal halide projector luminaires, depending on the colour rendering required. When using medium spread bi-symmetrical floodlights, the projectors should be placed at a distance from the building one-quarter that of its height. Fig.9 shows this in diagrammatic form. A suitable floodlight for this appli­ cation is the Philips 616 Decoflood (Fig.12). This unit can use lamps rated at up to 150 watts, has a light output ratio of 0.58 and a bi-symmetrical beam spread. The electrical control gear for the lamp is built into the housing. Columns need a different type of floodlight and luminaire location if they are to be shown at their best. In this case, narrow-beam projectors are placed much closer to the building to illuminate the columns, with Fig.11 showing the recommended ap­proach. A suitable luminaire for this type of application is the Philips SVF100 (Fig.10). This can be fitted with a high pressure sodium lamp having a maximum power of 100 watts and gives a symmetrical beam spread of just 12°. The luminaire is aimed so that the maximum beam intensity is at the top of the column. Architectural accents – such as statues or other relatively small highlights – are illuminated by sym­ metrical beam projec­ tors, with the Fig.11: columns are illuminated with narrow-beam projector lumi­naires, positioned quite close to the building. It is recommended that ‘d’ be 1/12th of ‘h’ and that the beam be aimed at the top of the column. object bathed in one or more pools of light. An example of such a luminaire is the Philips 607 Decoflood, which is available in either high pressure sodium or metal halide forms with lamps of up to 400 watts power. It has a light output ratio of 0.83 and its aluminium reflector gives a very narrow beam. Several of these floodlights are March 1998  7 Table 1: Typical Illuminance Values Surroundings (Illuminance in Lux) Building Material Luminaire location The direction from which the build­ ing or monument is to be viewed will help determine the position of the lights. If glare and distraction are to be reduced, the lights should be kept out of sight of the viewing points and this is sometimes done by par­tially locating the luminaires underground. Alternatively, asym­metric floodlights can be used which direct no light at all behind the body of the luminaire. Floodlights are often aimed so that Metal Brightly Halide Sodium Clean Dirty Li t Lamp Surface Surface Lamp Poorly Li t Well Li t Light Stone 20 30 60 1.0 0.9 3.0 5.0 Dark Stone 100 150 300 1.0 1.1 2.0 3.0 Aluminium Cladding (natural finish) 200 300 600 1.2 1.1 1.5 2.0 Fig.12 (left): the Philips 616 Decoflood is suitable for illuminating building facades. It is available in either high pressure sodium or metal halide lamp forms. The control circuitry is contained within the housing. often used in a given situation so that the feature can be “modelled” by the light. Correction Coefficient they act differently on adjoining parts or planes of the building. Fig.13(a) shows the lights positioned so that the each facade will each appear to have a different brightness when viewed from position ‘V’. Using these lighting angles will also help bring out any textures that may be present on the two surfaces. Conversely, Fig.14(b) gives equal illuminance across both surfaces and will make any surface texture less visible. Illuminance values The illuminance required to give the right degree of visual impact depends on a number of factors, in­ cluding the environment in which the building is situated. If it stands alone in a dark space, less illuminance will be needed to give the same impact. Conversely, a bright environment will require a higher degree of illuminance to give the same visual impact. If the building has a dark surface finish, a higher illu­ m inance will be needed. A dark surface can be a characteristic of the materials from which the building is constructed or can be the result of fouling over a period of time. Another aspect to consider is the texture of the building material. In a normal installation where the light is directed up at the building, the smoother the surface, the lower the amount of reflected light that will reach the viewer. Finally, if the lamp chosen has a high spectral output that’s close to the colour of the build­ ing, less illumination will be required. Table 1 gives some recommended illuminance values, with the values valid for tungsten lamps having a col­ our temperature of 2800K. If you were designing a floodlighting system, you would certainly hope to be illuminat­ ing a light-coloured stone build­ing! Conclusion The floodlighting of buildings requires careful planning and con­ sideration of the luminaire and lamp types to be used. Next time you pass a floodlit building at night, it’s worth studying how the designer has gone about the task. Next month, in Part 6, we will take a look at the low pressure sodium vapour lamp. Fig.13: with the floodlights positioned at ‘S’ and the viewer at ‘V’, in (a) the relative brightness of the two walls will appear different and the textures will be strongly modelled. In (b) the brightness will be even and the lighting flat. 8  Silicon Chip Acknowledgement: thanks to Philips Lighting for making available the illustrations used in this article. SC