by John Mardaljevic, Professor of Building Daylight Modelling at Loughborough University
It is fitting that the Daylight website sees a major ‘relaunch’ in 2013 – the centenary year of the International Commission for illumination (or CIE by its French acronym) http://paris2013.cie.co.at. We have witnessed in recent years an unparalleled level of activity in the field of daylighting research and application. Much of this effort has been to refine – in the broadest possible sense – our understanding of what constitutes ‘good daylighting’. Fundamental to this has been the establishment of the link between daylight provision and the prevailing climate. Or rather, the re-establishment of that link since the 1970 CIE document “Daylight”, published over forty years ago, is quite emphatic that measures such as the daylight factor should be used together with climate data to estimate the annual provision of, say, 300 lux of daylight. Somehow, over the intervening decades, we seem to have lost sight of the fact that estimating daylight provision from climate data used to be seen as an integral part of the daylight factor method. One of the proposals currently before the EU Standardisation Panel TC169/WG11 is to re-establish this neglected link. This would lead to recommendations for higher daylight factor values for those locales where there is less daylight availability – surely, a step in the right direction. The perceived inadequacy of current standards has led some notable daylight experts to recommend that the standards should be ignored altogether http://www.cibsejournal.com/archive/PDFs/CIBSE-Supplement-2012-12.pdf. Such sentiments are understandable. However, if the standards are proving to be insufficient to ensure a high likelihood that a good daylighting design is achieved, then we should look to improving them rather than ignoring or ditching them altogether.
Estimating daylight provision from climate files involves use of the sky illuminance data only. To account for contributions from both the sun and the sky requires a rather more precise computational method called ‘climate-based daylight modelling’ (CBDM). This is acknowledged to be a major advance in the field of daylight modelling, and has opened up numerous opportunities to investigate daylighting and daylight-related phenomena. This activity has inevitably led to the formulation of metrics founded on CBDM, e.g. Useful Daylight Illuminance (UDI) and Daylight Autonomy (DA) http://www.ies.org/leukos/download_G.cfm?art_id=105. Just a few months ago the US Illuminating Engineering Society published their ‘Approved Method: IES Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE)’ document (IES LM-83-12). We will no doubt see further developments in the area of metrics in the near future, and also more vociferous advocacy of CBDM as the basis for the next generation of daylight metrics.
Planning in the UK has recently become a ‘hot topic’, and the Law Commission for England and Wales has just begun a public consultation on the arcane practice of ‘Rights of Light’. http://www.bbc.co.uk/news/uk-21516369 http://lawcommission.justice.gov.uk/consultations/rights-to-light.htm Whilst possession of a ‘Right of Light’ can result in the prevention of a development that would cause undue daylight injury (according to the basis established nearly a century ago), in reality the measure used equates to very low levels of daylight illumination – much less than what any of the design guidelines recommend – and the practice is long overdue some reassessment. Whatever transpires with the consultation on Rights of Light, more general planning guidelines are perhaps also due some reassessment. Not least because the findings of a survey in the UK carried out by the Future Homes Commission has revealed that home buyers in Britain show a high level of dissatisfaction with many new-build properties. In particular, the report noted that of those participating in the survey “63% ranked high level of natural light in the rooms as of the highest importance in a home”. http://www.ribablogs.com/files/FHCHiRes.pdf That figure alone should be sufficient for developers to pause and reconsider their priorities. Whatever the immediate financial constraints, the creation of thousands of undesirable properties is surely in no one’s long-term interest.
Both the basis for daylight evaluation and the role that it plays in the building design process are at a crossroads. The increasing importance that daylight has in the performance evaluation of buildings for compliance purposes has led to a re-evaluation of much of the ‘accepted wisdom’ that has passed down over the years. Scientists are now beginning to understand the mechanisms and processes for various daylight-related phenomena generally referred to as ‘non-visual effects’. To understand the relevance of these effects for buildings, daylighting researchers have begun to forge links with photo-biologists, psychologists, environmental scientists, etc. And so researchers entering the field of daylighting today are presented with numerous opportunities to lay the foundations for the next century of daylighting research.
John
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John Mardaljevic
Professor of Building Daylight Modelling
School of Civil & Building Engineering
Loughborough University
Loughborough
Leicestershire
LE11 3TU, UK
http://www.lboro.ac.uk/departments/cv/staff/profile/367.html
Personal daylighting website: http://climate-based-daylighting.com
