Efficient Lighting
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The lighting of a building should be considered early in the design stage, because it is at this stage that the major decisions affecting switch controls or the daylighting are made. It is possible to make changes to the electric lighting system during the life of the building easily, but significant changes to the circuitry or daylighting are very much more difficult and costly, although they may be cost effective.

Energy-efficient artificial lighting design

Some lighting installations are designed to produce a uniform illuminance over the entire space. Although this allows flexibility in positioning work stations, the appearance of the space can often be somewhat bland. Areas where lower levels of lighting would be adequat, such as circulation space, if lit to the same level as areas such as work stations where higher illuminances are needed for the detailed visual tasks carried out there, this arrangement is clearly wasteful. Improvements in energy efficiency and reductions in costs can be obtained by matching the lighting to the requirements. This can be achieved by a system of localised lighting, where luminaires are related to the work stations; for example, lighting provided either by suspended luminaires, or by uplights. An alternative approach is to install a uniform array of luminaires and then to adjust the light output of each individual luminaire to match the requirements of the area it lights. This latter approach is simply achieved with some of the most recently introduced electronic control systems.

For other applications, such as hotels, the designer would consider more “mood” lighting as being appropriate but energy efficient lamps in achieving this target can also be effective. For the retail application the designer needs to take care to the requirements of vertical illumination to enhance the appearance of the merchandise. Even for domestic dwellings energy efficient lighting can be used with good effect, care should be taken when utilising energy efficient lamps and when using CFL’s use those that are designed into the luminaire. If plug-in CFL’s were to be used there is no assurance that the occupier will not revert back to the less energy efficient lamps such as tungsten at the time of replacement.

Optimise daylighting

Daylight within a building has a major effect on the appearance of the space, and can have considerable energy efficiency implications. Building occupants generally prefer a well-daylit space, provided that problems such as glare and overheating are avoided.

The major factors affecting  the dayligting of an interior are the depth of the room, the size and location of windows and rooflights, the glazing system and any external obstructions. These factors usually depend on decisions made at the initial design stage of the building, e.g. whether the building is deep or shallow plan, whether it is single storey, allowing the use of rooflights, or multi-storey. Appropriate planning at this early stage can produce a building that will be more energy efficient as well as having a pleasing internal appearance.

Changes to the daylighting of an existing building requires major work, although this may improve the energy efficiency of the building as a whole and be cost effective. More daylight can be admitted to a building, for example by the addition of rooflights, lighting shelves or prism panels. Alternatively, the daylight entering may be reduced as a consequence of other works, for example the recladding of an overglazed building to improve its thermal performance. It is important in this case that the window size is not reduced to the point where the electric lighting is required whenever the space is occupied, negating some of the benefits of the reduced heat losses.

In a well-daylit building, daylight often provides sufficient illumination for activities such as circulation for the greater part of the day, and can provide adequat working lighting for a substantial part of the year. However, to utilise fully the benefits of daylight in an interior, it is important to ensure that the electric lighting is turned off whenever daylight provides adequat illumination. This is achieved by the use of appropriate lighting controls, and may involve some degree of automation.

It is important to avoid problems of glare and overheating, and appropriate shading devices should be provided. These may be either fixed, such as fins on the outside of the building, or moveable, such as venetian blinds. Studies have shown that there is considerable potential for improving energy efficiency using this passive solar approach to building design exploiting daylight to displace electric light. This potential clearly depends on the local climate, in particular the priorities in the warmer, brighter conditions of the Mediterranean countries will be different from those in the cooler, cloudier climate of northern Europe.