Energy efficiency has a direct influence on running costs. But there is a second and more important aspect to energy efficiency and that is aiding the reduced use of electricity, which contributes to global warming and climate change. For these reasons, the Government has asked for a 15%reduction in hospital primary energy consumption by 2010, plus target energy uses of 35–55 GJ/100 m3in new facilities and 55–65 GJ/100 m3inexisting ones. Lighting forms an important part of this. For example, a recent survey by a lighting manufacturer estimated that if all the T12 fluorescent tubes in a large hospital were converted to T8, an annual energy saving of £27,000 could be realised; a substantial saving with just one measure. An estimate based on Building Research Establishment (BRE) data suggests that national savings of 80 GWh/yr, worth roughly £4 million annually, could be achieved by another simple measure, replacing tungsten lighting with compact fluorescent lamps in hospitals. A further 70 GWh/yr (£3.5 million) could be saved by the cost-effective deployment of suitable lighting controls.
Energy efficiency in lighting is measured in terms of the light provided and the energy it consumes. The light provided by a lamp is measured in lumens, the basic measurement unit of light. The energy it consumes is measured in watts, which includes not just the lamp wattage, but the energy consumed by any ancillary circuitry that is necessary to operate the lamp, for example a fluorescent lamp ballast. A lamp’s energy-efficiency rating, or efficacy, is described in lumens per watt. But this only describes the lamp, whereas the efficiency of a light fitting, or luminaire, is also important. This is usually defined in terms of a luminaire’s “light output ratio”(LOR). This is the proportion of the lamp’s light output that emerges from the luminaire in the directions required and is expressed as a decimal. Therefore, the efficiency rating of a luminaire is a combination of the lamp’s efficacy and the luminaire’s LOR.
Using energy-efficient lighting equipment is an obvious aim but it must be balanced by visual performance requirements. It also means only applying the lighting required for both the task and appearance, which does not mean flooding the whole areas of a hospital space with light that is unnecessary. The lighting installation needs to be designed to not only provide the lighting required, but also control it to the best effect. Examples of this are switching lighting off when there is sufficient daylight or when rooms, or areas, are not occupied such as toilets and bathrooms. This will require the lighting circuits to be planned with this in mind. For example, zoning lighting circuits relative to the windows so that those nearest the window can be switched off while those furthest from the windows can be left on as necessary. Positioning and labelling of switches can help with this but in some cases automatic controls might be appropriate; however, for hospitals the designer must be sure that these will not interfere with the hospital’s operation.
Lighting energy-efficiency measures are now included as part of the Building Regulations Part L and designers and users need to be aware of this and consult the relevant documents.
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