Authors: Dr Kevin Kelly is head of electrical services engineering, Dublin Institute of Technology and James Thomas Duff, Arup and PhD student, Dublin Institute of Technology Recent changes to the SLL Code for Interior Lighting (2012) are affecting lighting design in Ireland, the UK and internationally. Lighting design is one of the fastest-changing areas in engineering at present. Interior lighting design has evolved significantly in recent years, due to changing technology and demands for reduced energy. New recommendations change previous demands for equal illuminance across an entire space and make new recommendations for qualitative metrics and distribution of light, combined with demands for control and energy efficiency. [login type="readmore"] Increased demands for more daylight linked to improved lighting control are increasingly leading to more holistic design with the need for architects, engineers and facilities managers to work more closely to provide a holistic solution. Light-emitting diode (LED) lamp technology is expected to be a €65 billion industry by 2020, with this technology improving at an exponential rate. But LEDs can be expensive and are not without problems. This is an exciting and challenging time for the lighting industry. We are challenged to provide holistic robust solutions that maximise the benefits of new technologies, whilst protecting our clients from poor-quality lighting products and installations. CURRENT GUIDANCE AND ITS LIMITATIONS In Ireland, the UK and many other parts of the world, the foremost authority on interior lighting is the Society of Light and Lighting (SLL), previously named the Illuminating Engineers Society and founded in 1911 [1]. It has set guidance for the industry since 1936 and writes a wide variety of design guides for the lighting sector, which are widely adopted throughout the world. The SLL’s Code for Lighting and accompanying Lighting Handbook provide a summary of lighting standards and offer further qualitative guidance, which combines to provide a comprehensive text on lighting. In recent years, the European Committee for Standardisation (CEN) has also set standards for all countries in Europe. Although there are many standards, in the foreground are EN 12464 Lighting for Workplaces and EN 15193, the Energy Performance of Buildings Directive. In EN 12464, minimum requirements for lighting are laid down for both interior (part one) and exterior (part two) lighting. EN 12464 specifies many quantitative criteria, but the most prominent are maintained illuminance, uniformity, colour rendering index and unified glare rating [2]:

  • Maintained illuminance is the quantity of light that an installation will provide at the end of a maintenance cycle;
  • Uniformity is the ratio of the average illuminance compared to the minimum illuminance;
  • Colour rendering index is a measure of the appearance of colours under certain light sources; and
  • Unified glare rating is an estimation of visual comfort.
Within EN 15193, a specific method for the calculation of lighting energy consumption that goes beyond W/m2 is described. In recent years, standards have changed. The full implications of this are explained elsewhere [3], but the main changes are: increased room surface reflectances; minimum quantities of illuminance on major room surfaces; a move from illuminating an entire horizontal space at working plane height to focusing light onto where it is needed; the introduction of metrics which account for illuminating objects and peoples’ faces within a space; and the proposition of an alternative method for calculating energy consumption that better accounts for use of daylight and control mechanisms [2][4][5]. Increased room-surface reflectances will allow for an increased quantity of reflected light, which will increase the brightness of a space [6]. Specifying a minimum quantity of light on the major surfaces of a space will ensure that there is enough light available so that reflected light will contribute to the appearance of the space [2]. It is no longer recommended to illuminate an entire space at working plane height to a given illuminance level. It is now suggested that lighting designers work with their design team to finalise the task area within a space and illuminate this to a suitable illuminance, with the remainder of the space illuminated to a lower illuminance [2]. The aim of this is to provide visual interest, which has been shown to increase occupant satisfaction within spaces [14], and reduce energy consumption. The introduction of cylindrical illuminance and modelling index are stated as being “a big step forward in recognising the importance of the visibility of objects, particularly peoples’ faces, within a space” [8]. Minimum levels of cylindrical illuminance and an appropriate modelling index will highlight objects, reveal textures, aid facial recognition and allow for better integration of electric lighting and daylight [2][8][9]. [caption id="attachment_8158" align="alignright" width="241"] Fig 1. Cylindrical illuminance (SLL Code)[/caption] Figure 1 illustrates illuminance considered on the cylinder; this is an important metric of light when considering modelling. Figure 2 illustrates diffuse lighting, directional lighting and a combination of side and diffuse lighting respectively. Both illustrations are from the SLL Code for Lighting. Standards, however, do have their limitations. In a search for what exactly the purpose of lighting guidance is, Boyce attempts to define lighting quality: “Bad quality lighting does not allow you to see what you need to see, quickly and easily and/or causes visual discomfort. Indifferent quality lighting allows you to see what you need to see quickly and easily and does not cause visual discomfort, but does nothing to lift the spirit. Good-quality lighting allows you to see what you need to see quickly and easily and does not cause visual discomfort, but does raise the human spirit [10]. He later proceeds to show that lighting guidance will only eliminate bad lighting and produce indifferent lighting [11]. It will do little to produce good quality lighting [11]. Boyce suggests that at present, to produce good quality lighting, a team of a talented architect and a creative lighting designer are necessary [11]. This shows the limitations of lighting guidance and standards; simply following them will not produce good quality lighting. Boyce explores methods which may bridge the gap between indifferent and good-quality lighting and proposes that if none of these are accepted in the future, then good-quality lighting will only be available to those that can afford the services of a creative, experienced and talented lighting designer [11]. DAYLIGHT, BIM AND HOLISTIC DESIGN [caption id="attachment_8160" align="alignright" width="884"] Fig 2. Modelling illustrated (SLL Code)[/caption] People love daylight and spaces that make extensive use of it are generally considered attractive, but they do not love it unconditionally [12][13]. Like many other light sources, daylight has to be controlled to avoid visual discomfort as well as thermal discomfort. Provided this is done, then daylighting through windows can create a bright and interesting visual environment – these are the dimensions by which people assess the quality of a space [14]. Variation of daylight throughout the day delivers meaningful information about the passage of time and the view out can provide useful stimulation [14]. Buildings where daylight is thoughtfully distributed without visual or thermal discomfort are considered better buildings [12]. Maximising daylight and minimising energy used by electric lighting must take place in a way that minimises overall energy consumption from the building. It is unacceptable to maximise daylight to reduce light energy if thermal energy requirements increase due to the need for extra heating or cooling. It should be remembered that extra glazing would increase heating load in winter and cooling load in summer, whilst electric lighting can also contribute significantly to building cooling load requirements. So this is a complicated balance, which varies with building type, construction, orientation, usage and location. It is generally agreed in the UK and Ireland that the way to address this challenge is to use a holistic design approach, integrating the design of the architecture, glazing and engineering design. Input is needed by the architect, structural engineer, heating and ventilation engineer, electrical engineer, lighting designer, interior designer and control systems engineer. Modern building information modelling (BIM) software facilitates such multi-disciplinary interaction and its use is growing exponentially in construction projects in this part of the world. Adopting BIM for construction projects is considered similar to adopting email when it first became freely available, in that businesses that do not adapt will be left behind. BIM allows lighting designers interact with the design team when early architectural decisions are made to provide input to decisions about building size, shape, construction type, orientation and glazing. The role of the heating and ventilation engineer is also crucial at this time, so that potential solar gains can also be estimated for these variables. BIM software facilitates design changes and orientation variation in a cross-disciplinary way to optimise design, maximise customer and user satisfaction whilst minimising energy and other costs for the building. In your next issue of the eJournal, the authors will analyse the pros and cons of LED lighting and take a look at lighting controls. Are they the answer to your lighting problems? Dr Kevin Kelly is head of electrical services engineering in the Dublin Institute of Technology. He is also the president of the Society of Light & Lighting for 2013/14. James Thomas Duff works for Arup, Dublin and is a PhD student in Dublin Institute of Technology. References: [1] Loe, DL and McIntosh, R. 2009. ‘Reflections on the last One Hundred Years of Lighting in Great Britain.’ The Society of Light and Lighting, as part of CIBSE. Page Bros. Norwich. [2] Committee of European Standards. 2011. EN 12464-1:2011. ‘Light and Lighting – Lighting of Workplaces. Part 1: Indoor Workplaces’. London: CEN. [3] Duff, James Thomas (2012) ‘The 2012 SLL Code for Lighting: the Impact on Design and Commissioning.’ Journal of Sustainable Engineering Design: Vol. 1: Iss. 2, Article 4. [4] Committee of European Standards. 2011. EN 12464-2:2009. Light and Lighting - Lighting of workplaces. Part 1: Outdoor Workplaces. London: CEN. [5] Committee of European Standards. 2006. EN 15193:2006. Energy performance of buildings — Energy requirements for lighting. London: CEN. [6] Duff, JT, Kelly, K. "In-field measurement of cylindrical illuminance and the impact of room surface reflectance on the visual environment" Proceedings of the SLL and CIBSE Ireland International Lighting Conference, Dublin, 2013. [7] Wen, Y-J, Agogino, AM. 'Control of wireless-networked lighting in open-plan offices.' Lighting Research and Technology 2011, Vol 43, pp235-248. [8] Society of Light and Lighting. 2012. The SLL Code for Lighting. CIBSE. Page Bros. Norwich [9] A Nassar, MM El-Ganainy, FA Moktader, SM El-Kareem, and MA Haridi. Cylindrical Illuminance and its Importance in Integrating Daylight with Electric Light. Lighting Research and Technology, September 2003; vol. 35, 3: pp. 217-222 [10] Boyce PR. 'Lighting Quality: The Unanswered Questions.' Proceedings of the first CIE symposium on lighting quality, Ottawa 1998. [11] Boyce PR. ‘Lighting Quality for All? Proceedings of the SLL and CIBSE Ireland International Lighting Conference,’ Dublin, 2013. [12] Veitch, JA, Galasiu, AD. ‘Occupant preferences and satisfaction with the luminous environment and control systems in daylit offices: a literature review.’ Energy and Buildings 2006, Vol 38, pp728-742. [13] Al Marwaee, M., Carter, DJ. ‘A field study of tubular daylight guidance installations.’ Lighting Research and Technology, 2006, Vol 38, pp241-258. [14] Boyce, PR. Human Factors in Lighting, London: Taylor and Francis, 2003.