This is the third post in the current sequence of three where we review key aspects of how our heritage buildings influence our health and well-being: this week we focus on daylight. How important is daylight? As Earth inhabitants our whole being has evolved according to the circadian rhythm: it is only since 1879 when Eddison’s artificial light was invented that we have been able to meaningfully extend our natural waking hours far beyond what our bodies naturally manage well. A broad subject, but suffice to say our relationship with natural daylight is fundamental to our physical and mental well-being and impacts our non-visual processes (Paradise, 2014). For example, it has been found that exposure to daylight can increase human productivity by 15 percent (World Green Building Council, 2018). How can we maximise the benefits of daylight? Spatial Layout The layout of the interior of the building would ideally follow the natural course of daylight to provide the highest health and well-being benefits – for example sleeping locations should be located in east-facing rooms to maximise the stimulating benefits of sunrise. Similarly living spaces should face south and west. New Well Positioned Windows If you live or work in a heritage building you may not have the flexibility to make windows larger if the exterior is controlled by the local authority (Listed or in a Conservation Area). If you are considering works to your property do discuss options for creating new window openings with a conservation architect to review the potential benefit, and implications. Sometimes a well-placed modest window may be of greater benefit that widening an existing opening. The height of the head of a window affects how deep light will penetrate into a room: the depth of penetration is 1.5x the height of the window head. Therefore enlarging an existing window into doors will have little effect upon the daylight penetration into the room. Paradise (2014) references research which state the changing levels of daylight create a positive stimulus for occupants. Large expanses of windows providing even light levels are not as stimulating. Glass Technology If you do not have heritage glass in windows and doors and are planning to replace your existing glass consideration should be given to the glass design. For good daylighting the visible light transmittance (VLT) of the glass should be high and the solar heat gain coefficient (g-value) should be low (Ece, 2018). Glass Cleaning Dirty glass can considerably hinder light transmittance through a window! Reflective Surfaces ‘Reflectance values from room surfaces will significantly impact daylight performance and should be kept as high as possible.’ It goes on to recommend keeping ceiling reflectances over 80%, walls over 50%, and floors around 20%.’ (Ander, 2016). Interior Colours As a rule of thumb opt for lighter colours. It is wise, however, to review colour selections with an interior designer to achieve a degree of cosiness with an effective balance of deeper colours. Mirrors can be used in key locations to bounce what light arrives into the room even further. Should daylight be controlled? Glare Excessive daylight in a room can be visually uncomfortable. Glare can be reduced by using blinds or curtains of various transparencies. Personal control over daylight is both practical and enhances perceived levels of comfort. In conclusion Research of daylight within buildings as impacts our well-being is still developing, however all of the above factors are known to have an effect. As an occupier of a heritage building there is much you can do to manage daylight to improve your well-being, however we do recommend seeking an informed over view from an appropriate professional – the list above could be used to frame your discussion with them. Living with heritage buildings, not despite them, can be a learning curve, but a great place to start is connecting with Heritage Revival via this blog. During 2019 blog posts are scheduled for release on Fridays every fortnight. Do follow us so you don’t miss an update. References Ander, G.D. (2016). Daylighting. Whole Building Design Guide. [Online]. 15.09.16. National Institute of Building Sciences. Available from www.wbdg.org/resources/daylighting. [Accessed 24.02.19]. Ece, N. (2018). Building Biology: Criteria and Architectural Design. Beltz Bad Langensalza GmbH, Germany. Paradise, C.L. (2014). Daylight and glazing specification: The impact on non-visual processes. Submitted in candidature for the award of PhD. [Online]. Available from www.orca.cf.ac.uk/75610/1/CParadise%20PhD_30062015%2Bblanks.pdf. [Accessed 24.02.19]. World Green Building Council. (2018). A guide to healthier homes and a healthier planet. [Online]. 04.12.18. Available from www.worldgbc.org/sites/default/files/20181204_WGBC_Homes-Research-Note_FINAL_spreads.pdf. [Accessed 28.02.19].  Paradise, C.L. (2014) explores in depth the impact of daylight upon occupants’ well-being.