Lighting : LIGHTING Feb-Mar 2018
52 LIGHTING MAGAZINE | February/March 2018 As for the need to develop new objectives for lighting, this is where we enter the realm of human-centric lighting. Human-centric lighting is lighting designed to bring out the full range of effects that exposure to light can have ranging from the familiar visibility and visual discomfort to increased alertness, better mood and motivation, and improved health and well-being. To some, human-centric lighting is nothing more than a commercial bandwagon designed to sell product while for others it is legitimate approach to better lighting quality. Human-centric lighting can be considered to have both a width and a distance. The increased width is evident from the list of potential effects given above. The distance occurs because whereas visibility and visual discomfort can be closely related to lighting conditions, the other effects are related to many factors, lighting conditions being just one of them. This is particularly so when the outcomes claimed, such as better learning in schools, are far removed from the obvious effects of lighting. Given this situation what is the designer to do? One answer would be to ask a series of questions of anyone claiming some remote effect for lighting: Is the claimed effect statistically significant; if it is, what is the effect size and is it worth bothering about; has the effect been replicated; what is the mechanism for the effect and are there where the claimed human–centric effects of light can be shown to be reliable and sizeable. If all or even some of these changes occur the result will be a greater complexity in design because of the diversity in objectives for lighting and a greater number of metrics to describe lighting. Further, for many of these objectives the outcome will become a matter of probability rather than certainty. Such a situation will call for greater transparency from both designers and manufacturers if confusion and chicanery are to be avoided. Finally, it is a pleasure to acknowledge the contributions of Mark Rea and Kit Cuttle to many of the thoughts expressed in this lecture. Although separated by thousands of miles, modern communications have enabled many stimulating discussions with them for which I am extremely grateful. It is only fair to say that while they would undoubtedly agree with some of the content of this lecture you can be sure that they would not agree with all of it. FOOTNOTES i This paper was the 30th Trotter Paterson Lecture to the Society of Light and Lighting (SSL), presented on 6th July 2017, at the Bishopsgate Institute, London. It was later published in the SSL Newsletter. The figures were prepared by Dennis Guyon of the LRC REFERENCES 1. Rea MS. Value Metrics for Better Lighting, Bellingham WA; SPIE Press, 2013 2. Rea MS. The lumen seen in a new light: Making distinctions between light, lighting and neuroscience. Lighting Research and Technology 2016; 48: 259-280 3. Rea MS, Bierman A. A new rationale for setting light source luminous efficacy requirements. Lighting Research and Technology. First published 10 September 2016 DOI 1477153516668230 4. Lin Y, Wei M, Smet KAG, Tsukitani A, Bodrogi P, Khanh TQ. Colour preference varies with lighting application. Lighting Research and Technology 2017; 49: 316-328. 5. Teunissen C, van der Heijden FHFW, Poort SHM, de Beer E. Characterising user preference for white LED light sources with CIE colour rendering index combined with a relative gamut area index. Lighting Research and Technology 2017; 49: 461-480. 6. Illuminating Engineering Society of North America. Technical Memorandum TM-30-15 IES Method for Evaluating Light Source Color Rendition New York: IESNA, 2015. 7. van Kemenade, JTC, van der Burgt PJM. Light sources and colour rendering: Additional information for the Ra Index, Proceedings of the CIBSE National Lighting Conference, Cambridge, London: CIBSE, 1988. 8. Narendran N, Freyssinier JP, Zhu Y. Energy and user benefits of improved illuminance uniformity in parking lot illumination. Lighting Research and Technology 2016; 48: 789-809 9. Tashiro T, Kawanabe S, Kimura-Minoda T, Kohko S, Ishikawa T, Ayama M. Discomfort glare for white LED light sources with different spatial arrangements. Lighting Research and Technology 2015; 47: 316-337 10. Scheir GH, Donners M, Geerdinck LM, Vissenberg MCJM, Hanselaer P, Ryckaert WR. A psychophysical model for visual discomfort based on receptive fields. Lighting Research and Technology. First published 29 July 2016 DOI 1477153516660606 11. Yang Y, Luo MR, Ma SN. Assessing glare Part 2: Modifying unified glare rating for uniform and non-uniform LED luminaires. Lighting Research and Technology. First published 5 April 2016 DOI 1477153516642622 12. British Standards Institution, (2011a) BS EN 12464-1:2011 Lighting of Workplaces – Part 1 Indoor Workplaces, London: BSI. 13. Cuttle C. Towards the third stage of the lighting profession, Lighting Research and Technology 2010; 42: 73-90. 14. Cuttle C. A new direction for general lighting practice, Lighting Research and Technology. 2013; 45: 22-39. 15. Hawkes RJ, Loe DL, Rowlands E. A note towards the understanding of lighting quality, Journal of the Illuminating Engineering Society 1979; 8: 111-120. 16. Cuttle C. Lighting Design: A Perception Based Approach. Abingdon, UK: Routledge, 2015 17. Berson DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock, Science 2002; 295: 1070-1073. 18. Riemersma-van der Lek RF, Swaab DF, Twisk J, Hol EM, Hoogendijk WJ, van Someren EJ. Effect of bright light and melatonin on cognitive and non-cognitive function in elderly resident in group care facilities: A randomised controlled trial, JAMA 2008; 299: 2642-2655. 19. Eastman CI. Circadian rhythms and bright light recommendations for shift work, Work Stress 1990; 4: 245-260. 20. Young CR, Jones GE, Figueiro MG, Soutiere SE, Keller MW, Richardson AM, Lehmann BJ, Rea MS. At-sea trial of 24h based submarine watchkeeping schedule with high or low correlated color temperature light sources. Journal of Biological Rhythms 2015; 30: 144-154 Figure 5. One way of expressing the hierarchy of lighting needs from the basic physiological to those of a more complex psychological nature (with apologies to Abraham Maslow). any converging measures that support the role of lighting? The answers to such questions can sort the wheat from the chaff. There are undoubtedly benefits of lighting beyond good visual performance without visual discomfort but until the claims made for human- centric lighting are examined with rigour, doubts about their validity will continue to be expressed. To sum up, general lighting practice is likely to be entering a period of flux over and above that already occurring with the rapidly spreading use of solid state light sources. Any changes to photometry and colorimetry metrics other than a simple replacement of CRI will require a lot of work by those who manufacture lighting equipment, those who prepare lighting recommendations and those who design lighting installations. Similarly, changing the primary purpose of lighting from lighting the task to lighting the space will require a very different approach by designers (Figure 5). Where the non-visual effects of light exposure can be shown to be beneficial, different types of lighting may be required as they will There are undoubtedly benefits of lighting beyond good visual performance without visual discomfort but until the claims made for human-centric lighting are examined with rigour, doubts about their validity will continue to be expressed.
LIGHTING December 17-January 18
LIGHTING Apr-May 2018