LIGHTING TECHNOLOGY


The Henderson Group has been supplied with Multivault GRP barrel rooflights from Brett Martin for its distribution centre in Belfast


commercial building types, this typically requires 10 – 20% of the roof area…’. The level of daylight for rooflit buildings is an inherent part of the building design. Because of the highly variable nature of daylight, a rooflight system is designed to deliver a likely occurrence of various daylight levels for a specified proportion of the day, averaged across the year, rather than a specific lux level as is the case with artificial lighting. To help architects and specifiers


achieve this a European CEN Standard for Daylight in Buildings (EN 17037) was first published in 2018. The standard has been adopted by all 34 CEN member states, including the UK in 2019. The version adopted by Britain is referred to as BS EN 17037.


Making the most of daylight potential


The Rooflight Association has published a new white paper – ‘The benefits of rooflights for the daylighting of buildings’ – that reveals an important message for large-span building owners and landlords. Paul Smith shares some of the key findings.


Paul Smith


Chair of The Rooflight Association’s technical committee


www.rooflightassociation.org T


including the shape, size and aspect of the building and its surroundings, plus the size, orientation and nature of the building apertures.


he ongoing discussion on the potential of daylight to reduce electric lighting consumption suggests that this remains


under-exploited, perhaps to a significant degree.


The amount of actual savings depends on the design, the control, and, ideally, the commissioning of an appropriate artificial lighting system. Electric lighting should be dimmed in response to available daylight and even switched off entirely if the daylight provision is both sufficient and relatively stable. It is evident from the data presented in our white paper that a typical specification rooflight building has considerable potential to reduce electric lighting energy consumption by efficiently utilising available daylight. To recognise the true value of any


natural resource, such as daylight, we must understand the degree of availability: how much and how often. The quantity and quality of daylight in a space depends on various factors,


EIBI | OCTOBER 2025


Spread of light For medium to large building types, rooflights offer the potential for excellent daylight uniformity due to the ability to have an uninterrupted regular arrangement, together with the design freedom to get the daylight where you need it. In this application, rooflights are beneficial when compared with vertical glazing, where guidance suggests the level of daylight


penetration is limited to approximately twice the window-head height (i.e., the height of the window above desk height) and the daylit area would therefore be limited to the perimeter of the building. For a given size and an unobstructed


setting, a horizontal rooflight can ‘see’ the entire sky (i.e. 180-degree angle) and therefore maximises daylight potential, whereas vertical glazing can ‘see’ only half of the sky (i.e. 90-degree angle), at best. Rooflights on large-span industrial buildings often experience little or no obstruction of the sky from other structures and therefore make them an obvious choice. Vertical glazing can still play a part in the overall daylight strategy of the building, where applicable.


The white paper is free to download at rooflightassociation.org


Maximise potential The white paper says that daylight must be considered an essential element in building design and that the right layout is critical to maximise the daylight potential within the building. The most effective layout balances internal requirements, like boosting natural light levels in deep-plan spaces, with practical considerations, externally, such as other utilities and photovoltaic panels on the roof. The white paper also gives guidance on the roof area apportioned for rooflights - ‘For non-residential industrial/


Recommended levels In the standard the levels of illuminance are informative only. They are recommendations and not mandatory targets. ‘Minimum’, ‘Medium’, and ‘High’ levels of illuminance are recommended for buildings with daylight openings in either a vertical (including inclined planes) or horizontal orientation. Increasingly important to building design is the internationally used WELL Building Standard which recognises that buildings directly impact physical and mental health, and the standard exists to make this a core part of architectural goals. Based in the US, the WELL Standard is applied worldwide. Version 2 of the standard - introduced in 2020 – adopted the methodology and recommended daylight levels of EN 17037 as an option to demonstrate compliance and is approved for buildings anywhere in the world.


Collective benefi ts As well as reducing the electric lighting burden, admitting daylight into your building also has significant benefits to the building occupants by keeping them in touch with the natural rhythm of the day with tangible health and well-being benefits. We have chosen to release this white paper now to clarify these benefits because, without research and strong data, daylighting and rooflights are in danger of being sidelined as decision makers favour photovoltaic systems to save energy and reduce carbon. However, by combining their collective benefits we can ensure the most favourable outcome for the building’s performance and the people working within them. ■


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