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Looking to the longer term

Apr 07, 2008
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Good lighting design can significantly reduce schools’ long-term energy costs, but it needs to be thought about at an early stage, says Greg Herring, product marketing manager at Cooper Lighting and Safety.

Designing a lighting scheme for a school can be a very challenging task. As well as having to provide the necessary light levels in an extremely diverse range of rooms and spaces – some of which will be multi-functional – the scheme must address the school’s need to keep ongoing costs to a minimum, especially with regard to energy consumption. And all this has to be achieved while staying within the inevitable project cost constraints.

Whether the project is a refurbishment or the blank canvas of a new build, the key to a successful scheme is the planning and integration of the lighting at an early stage to take advantage of available daylight, enhance architectural features and fulfil the requirements of the intended uses of each space.

All too often, however, lighting is not given enough consideration until the later stages of a building project, by which time overall cost pressures can place severe restrictions on the design of the scheme and undermine its ability to deliver the requisite savings. Cutting initial capital expenditure by lowering the specification and limiting features really can be the more expensive option in the long term.

Energy efficiency

With many competing demands on their budgets, schools try hard to keep running costs down, so one of the key design goals of any school lighting scheme should be reducing electricity consumption. This emphasis on energy efficiency is reinforced not only by legislative requirements in the form of Building Regulations but also by general environmental considerations such as carbon footprint targets.

One measure of the carbon footprint and sustainability of a building is the BREEAM scheme, which awards certification of a building’s green credentials through a weighted points system. Points are given for all aspects of how a building is constructed and managed with the weighting split over seven sections, examples being Energy and Transport, which accounts for 25% of the possible total and Health & Well-being accounting for another 15%. This scheme can play a key role in acknowledging environmental awareness, with green targets being a key objective for many local authorities.

As lighting typically accounts for over 20% of a school’s energy costs, the management and control of that lighting, if executed correctly, can play a vital role in achieving significant energy savings.

In this regard, it is important not just to look at the initial capital expenditure of a product or installation but to take a long view and consider the whole-life cost and relative payback period of a more efficient alternative. For example, simply moving to high-frequency control gear can typically bring energy savings of 20% compared with switch-start gear.

The lit environment

The latest CIBSE lighting guides seek to improve the lit environment in all types of buildings by eliminating the oppressive ‘cave effect’ of earlier lighting schemes, which was caused by the sharp cut-off and bright scalloping associated with ‘categorised’ louvres. In this respect, the lighting guides’ key recommendations are that average ceiling and wall illuminance levels, measured as a percentage of the average horizontal illuminance on the working plane, should be 30% and 50% respectively.

Meeting these requirements for ceiling and wall illumination usually means that either indirect lighting or additional wall-wash luminaires and uplighters will be necessary. Where ceiling height allows, suspended linear fluorescent luminaires can provide an element of upward light to wash ceilings and aid compliance with the lighting guides.

However, indirect lighting is inherently less efficient than direct lighting, and the use of additional luminaires inevitably increases energy consumption. So how can the designer create a lit environment that satisfies the human need for visual comfort while still managing to reduce overall energy costs?

Lighting controls

Rather than compromising the design of a good lighting scheme to achieve energy efficiency requirements, the answer is to use automated controls such as occupancy detection and daylight sensing to ensure that lighting is dimmed down or switched off when it is not needed.

Automated controls can be implemented either on individual luminaires or, by means of a simple Lighting Control Module (LCM), in zones. Acting as a central hub to which the luminaires in a particular area are connected, the LCM can control them as a group or with further split control based on inputs from various sensors. Such LCMs work especially well within typical classroom environments where there is often opportunity to maximise the use of daylight from windows or roof lights.

Diversity

In addition to these general considerations, a school lighting scheme needs to satisfy a variety of particular requirements according to the nature of the space to be lit and the tasks to be carried out. A typical school will therefore encompass an extremely diverse range of luminaires, from a storeroom lit by a simple fluorescent bulkhead to teaching areas illuminated by state-of-the-art fluorescent suspended systems with integrated occupancy and daylight management controls.

Fluorescent luminaires are not restricted to use in classrooms and corridors but are a versatile option with a multitude of luminaire types, for example utilising the latest T5 lamps and high-frequency control gear in guarded fixtures for sports halls or IP-rated luminaires for laboratories and kitchens.

Externally, areas such as car parks and walkways call for amenity lighting that not only delivers the necessary illumination levels but is also robustly constructed and sealed to withstand unfavourable weather conditions.

Display screen equipment

Any area where computers are used within schools – be it in classrooms, resource centres or IT suites - should be correctly lit using fittings with the appropriate cut-off angles and luminance levels in accordance with BS12464. These limits, which are specified at 65° from the vertical with screens vertical or inclined up to 15°, are typically 200cd/m2 for Class III VDT screens and 1000cd/m2 for Class I and Class II screens (screen classes as specified in ISO 9241-7).

Conclusion

While the detail of each school’s lighting scheme will be determined to a large extent by the design and intended use of its internal and external spaces, there will always be a general emphasis on energy efficiency in order to minimise ongoing running costs and satisfy environmental concerns.

Biography

Greg Herring is product marketing manager for mains lighting at Cooper Lighting and Safety, with responsibility for the development and marketing of the Crompton brand portfolio. He has nearly 10 years’ experience with the company, having originally joined as a product design engineer, progressing to senior product design engineer, then taking up the role of strategic sourcing engineer within the procurement department before being appointed to his present position early in 2007.