Energy Efficient Lighting in Buildings
Anthony I Slater
Building Research Establishment, BRE, Garston, Watford, WD2 7JR, UK
Summary
The energy consumed by electric lighting in buildings is substantial and represents a significant cost to the building occupier. For example, lighting energy costs are typically around 40% of the total energy costs in some types of office building. Energy consumption and its consequent cost is therefore important for the owners and occupiers of buildings. When looked at on a national or international basis the energy consumed by lighting is considerable. Improvements in energy efficiency can not only save costs over the life of the installation, but also help the environment by reducing gaseous emissions responsible for acid rain and the greenhouse effect. Appropriate technology is available to improve the energy efficiency of lighting significantly. Although these improvements often, but not always, entail an increased initial cost, some have relatively short payback periods, less than 2 years for some measures.
Lighting energy consumption depends on the electrical load and the hours of use. It is therefore affected by the design of a lighting installation to meet the lighting requirements of the space, together with its associated controls, and also its management in operation. The installed load required to satisfy the lighting requirements depends on the efficiency of the equipment: lamps, ballasts, luminaires and the properties of the space: the room size and surface reflectances. It is important to ensure that while the most appropriate equipment to meet the lighting requirements is used, it is also the most efficient equipment of its type. The most energy efficient lighting installations ensure that lighting is provided only where and when it is required. This may be achieved with appropriate design to produce either uniform general lighting or localised or local lighting.
The length of time the lighting is in use is determined primarily by the occupancy pattern of the space, but the ability of the occupants to control the lighting, for example switching on lighting only in those areas where it is needed, can have a major influence on energy consumption. The availability of daylight within the space can also affect the use of the lighting. The inclusion of a suitable lighting control system is therefore a major factor in ensuring energy efficiency.
When assessing the energy efficiency of a lighting installation, it is essential to consider both installed power and hours of use together. A higher installed load combined with a suitable control system to give low hours of use may result in a lower energy consumption than an alternative installation with a lower installed power but poorer control.
Although the technology to produce a lighting installation which meets the lighting requirements of the space energy efficiently is available, improvements are still being made and reports of some of the latest developments will be given during this conference. However, there are still many installations, which in practice fall below the highest standards. The reasons for this can often be traced to a lack of appreciation by the designers of the needs of the occupants, or changes which have occurred in the use of the space, but which have not been reflected by changes to the lighting. This can result in occupant discomfort or dissatisfaction and can lead to the lighting being used inefficiently.
Another major reason for poor energy efficiency is financial. The initial capital cost of an energy efficient installation may be greater, although the annual running cost will be less, than the cost of an installation which is meeting the same lighting requirements less efficiently. However it is important to consider the total life cycle cost of the installation. If the payback time of the more efficient installation is reasonable then a good financial case can be made for its adoption. Other reasons for not adopting the most energy efficient lighting solution may be a lack of knowledge of energy efficient practice or a lack of readily available information about the energy consumption of different products.
These barriers can be overcome and adoption of more energy efficient practice encouraged in a number of ways. These include: mandatory requirements, such as regulations and standards for lighting products or installations; labelling of products; charter or pledge programmes; promotional programmes and subsidies; educational programmes, including the promulgation of good practice codes and guides. These approaches have been tried in different countries and situations and reports will be given during this conference on the results of some of them.
There are various motives encouraging the adoption of more energy efficient practice, not least the wish to reduce the gaseous emissions associated with the consumption of electricity generated from fossil fuels, which contribute to the greenhouse effect. However these must overcome the barriers, such as the increased capital costs often associated with more efficient equipment. Energy efficiency can often be shown to be cost effective by considering life cycle costs and this consideration, which takes account of the broader picture, should be encouraged.
© Building Research Establishment Ltd - 1997
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