2011 - Daylight Symposium
DO WE KNOW ENOUGH YET TO PREDICT THE NON-VISUAL EFFECTS OF DAYLIGHT IN BUILDINGS? AN EXPLORATORY STUDY by John Mardaljevic
Speakers
John Mardaljevic (UK)
Founder/director
Daylight Experts Ltd
Previously thought of mainly in terms of task illumination and aesthetics/design, it is now believed that daylight in buildings might serve another purpose as the agent of a number of nonvisual effects. It has long been established that building occupants prefer an environment with daylight and views to the outside in preference to predominantly artificially lit spaces. In addition to these subjective preferences for daylit spaces, it is now firmly established that daylight has measurable biochemical effects on the human body, in particular with respect to maintaining a healthy sleep-wake cycle, i.e. circadian entrainment. Recent findings on these non-visual aspects of occupant exposure to daylight have led to a reconsideration of the function of daylight in buildings. Could the quality and nature of the internal daylit environment have a significant effect on the health of the human body which can be proven through the measurement of, say, hormone levels? Evidence is indeed suggestive of links between daylight exposure and both health and productivity indicators. The duration, intensity and spectrum of the light received at the eye are the principal factors determining the suppression in the production of melatonin by the pineal gland, and thus a key component in the entrainment of the circadian cycle – the maintaining of which is believed to have significant short and longterm beneficial health effects. Illumination levels are also believed to influence levels of alertness. An important factor in these considerations is the time of day when the light is applied. Compared to the luminous efficiency function of the eye, which has a peak value at 555nm, the action spectrum for the suppression of melatonin is known to be shifted to the blue end of the spectrum and has a peak around 450nm. Recent advances in experimental photo-biology have yielded sufficient data to calibrate models that allow, in principle, the quantification of the daylight stimulus required to induce non-visual effects.
In this presentation we describe the formulation of a model to predict the non-visual effects of daylight in buildings and demonstrate its application to a residential dwelling under various different building configurations and prevailing climates. These different building scenarios are used to show the sensitivity of the predicted quantities to various design and contextual (i.e. location and orientation) parameters. The model is founded on the climate-based daylight modelling (CBDM) approach, i.e. the prediction of absolute levels for luminous quantities over a full year and founded on standardised climate files. The CBDM approach was given several enhancements to account for the difference between the standard luminous efficiency function and the action spectrum for the suppression of melatonin. The various modelling procedures and assumptions are described in the presentation, and a novel means of visualising the ‘circadian potential’ of a point in space is presented.
John Mardaljevic is a Reader in Daylight Modelling at De Montfort University, Leicester, UK. His first degree and higher qualifications are: a BSc in Combined Physics with Maths, an MPhil in Astrophysics and a PhD in Daylight Simulation. Mardaljevic’s first significant contribution in the field of daylight modelling was the validation of the Radiance lighting simulation program under real sky conditions. Mardaljevic went on to pioneer the development and application of what has become known as climate-based daylight modelling. As an acknowledged world leader in daylight modelling, he was invited in 2007 to join the panel convened to revise British Standard 8206: “Daylight in Buildings”. In December 2008 the Board of Administration of the International Commission on Illumination (CIE) approved the formation of Technical Committee 3-47: Climate-Based Daylight Modelling following a proposal made by Mardaljevic earlier that year. In 2010 Mardaljevic was appointed ‘UK Principal Expert on Daylight’ for the European Committee for Standardisation CEN /TC 169 WG11.
