| LIGHTING while also reducing eyestrain, compared with unshaded daylight sources. An authoritative set of recommendations recently published by Brown et al9 included enhancing daytime melanopic exposure as measured by the International Commission on Illumination (CIE) melanopic equivalent daylight illuminance (m-EDI) (see boxout) by increasing access to natural daylight in the workplace, has been shown to improve sleep and increase objectively measured cognitive ofce worker performance. In work reported by Rohit Manudhane10 that explored the application of spectrally tunable lighting systems, he found that occupants preferred the variability in electric lighting that reected realtime daylight conditions, as illustrated in Figure 1, effected by a link to an outside light sensor. The recent extensive critical review undertaken by Vasque11 which considered the effects of window views, daylighting and lighting on occupants behaviour, perception, performance, and wellbeing came to a conclusion that the lack of standardisation across the studies often generated inconclusive results or results limited to the specic study conditions. It notes that more data and more standardised and comparable data is required. Abundant natural daylight can reduce the dependency on articial light, resulting in energy savings and reduced operational impact on the environment, as well as potentially improving workers physical and mental health and productivity. The World Green Building Council12 reported that overall, the evidence is unequivocal that ofce occupants prefer access to windows and daylight, which bring consistent benets in terms of satisfaction and health. Incorporating natural elements such as daylight and good ventilation can help mitigate the negative effects of hours spent indoors. Glazing units, including roof glazing, can make an important contribution to ventilation in buildings while also enhancing the quality of the space, as demonstrated in the multi-awardwinning UK Hydrographic Ofce (UKHO) headquarters in Taunton, Somerset, rated BREEAM excellent and shown in Figure 2. 0.012 Spectral power distribution (au) CPD PROGRAMME 0.010 0.008 0.006 0.004 0.002 0.000 400 450 500 550 Wavelength (nm) 600 650 700 Figure 1: The spectral distribution of light across the working day that provided the preferred environment for occupants, which emulated real-time daylight conditions (Source: CIBSE Journal10) Even when the majority of the outdoor air requirement is supplied by controlled, mechanical systems, having the option to open windows is important for building occupants to maintain some control of their personal environment and comfort. Rooight solutions may be employed to improve thermal comfort through natural ventilative cooling, as well as providing access to unobstructed sky and sunlight. This may complement vertical windows in external walls that might be signicantly constrained by adjacent buildings or other obstructions. BS EN 1703713 Daylight in buildings, rst published in 2018, is a code of practice that focuses completely on the quantity and quality of daylight for building users, by providing recommendations to deliver appropriate levels of daylight in any type of building. It fully recognises that the need to provide glazed openings and welldistributed daylight to interior spaces, while reducing articial lighting in use, must be considered with the balance between heat loss and solar gains. The standard notes that solar gains can contribute positively to heating but in warmer months, or where there is potentially unacceptable glare, solar shading should be provided either as static or moveable devices. BS EN 17037 sets minimum levels of performance, which can be assessed using simplied or detailed methods, to address each of four aspects of daylighting: Daylight provision is the amount of available daylight in habitable rooms this can be established by employing either climate-based modelling or daylight factor calculations. This directly impacts the likelihood of articial lighting being switched Figure 2: Opening rooights and vertical glazing provide natural ventilation and daylight for the UK Hydrographic Ofce (UKHO) headquarters building in Taunton that opened in 2019 (Source: AHR Architects www.ahr.co.uk/) MELANOPIC EQUIVALENT DAYLIGHT ILLUMINANCE (M-EDI) m-EDI, measured in lux, is the circadian metric adopted by the International Commission on Illumination (CIE) that accounts for the colour of the light (in terms of constituent wavelengths and intensity), the response of ve photoreceptors on the retina as related to the standard daylight spectrum (roughly the average midday light in western Europe, known as CIE D65). 56 December 2022 www.cibsejournal.com CIBSE Dec 22 pp55-58 CPD 209 VELUX Supp.indd 56 25/11/2022 16:19