Effects of light on humans

1. During centuries human beings lived to the rhythm of seasons like outdoor animals but nowadays, they spend most of their time indoor, in buildings. Some health issues, like seasonal affective disorder (SAD) which can be treated with luminotherapy, reveal that indoor lighting conditions are not always adapted to human metabolism and that humans can suffer from a lack of daylight. So, it is important that architects consider human need for daylight when designing a building. Physiological effect of light  Human visual system is perfectly adapted for daylight vision and color perception.  Light participates in the regulation of the internal human body clock. The human body clock is situating in the hypothalamus which links the nervous system to the endocrine system. It regulates different biological rhythms of the organism which are the ultradian (<24h), the circadian (~24h) and the infradian (>24h) cycles. The circadian cycle (from Latin circa about and diem day) regulates, among others, sleep cycle (melatonin), body temperature, sensation of hunger and mood (serotonin).  Vitamin D3 is necessary for the health of human bones and of intestine. The exposition to the sun and to UV waves is a way to produce this type of vitamin which can also be inhale.  Too much sun can also causes diseases like sunburns, skin cancer, eye damage and aging skin if no sun protection is provided. Psychologicaleffect of light The repartition of light in a room has an influence on impression of well being. The space could seem friendly, large, cold, … Effects of light on humans Sources : http://zaborina.i.ph/photo/108/109 Sources : http://www.accrosante.com/famille/sommeil.html

2. Effects of light on humans 1. Diseases linked to a lack of daylight  Circadian cycle Insufficient, inappropriate or not expected light can damage natural circadian cycle and entertain consequences on human being performances, on health or on his mood. Circadian cycle can be disturbed by jet lag, night-work jobs, night luminous pollution. Disturbed circadian cycle can causes: sleep troubles (insomnia or hypersomnia); appetite troubles; lack of energy and irritability (difficulty concentration, sad mood) When these symptoms appear around winter, we talk about seasonal affective disorder (SAD). It is probably the diminution of light intensity during these months which causes the trouble which is more often observed for women. During this period, an unusual rate of melatonin is observed for people suffering of SAD.  Vitamin D A lack of vitamin D can causes muscular tiredness and pains and increases risk of fracture. It is also associated with a highest risk of cardio-vascular diseases and cancer of breast. Sources : http://sommeil.univ-lyon1.fr/articles/challamel/sommenf/fig13.php

3. Effects of light on humans 2. Treatment  Luminotherapytreats SAD, insomnia and otherdepressivediseases in exposing people under a white light (spectrumsimilar to daylight) or blue light (peak spectral sensitivity of the circadian system) whichdoes not contain UV and IR. Recent studies have shown that blue light is interesting for stimulating circadian system when it is combined with the appropriate light intensity and duration. In fact, circadian rhythm and pupillary light reflex are involved by non-visual photoreceptors in the retina : photopigments called melanopsin. Peak spectral sensitivity of the circadian system is situated at about 460nm which correspond to blue light. Subjects exposed to blue light are more alert because the blue component of light stops production of melatonin, a hormone responsible for regulating sleep. In wearing glasses filtering blue light before bed, people suffering from insomnia will activate the secretion of melatonin and favor the sleep. Improving sleep time will have a positive impact on cognitive function and on mood. The use of blue light is also recommended for the treatment of Alzheimer. Sources : http://www.photobiology.info/Roberts-CR.html

4. Effects of light on humans Architects will take special attention to daylight in hospitals, centers of care,… They will control the availability of daylight in the rooms and will provide a sight to the patient. In residential architecture, architects will try to provide enough daylight in dining room, kitchen, etc. and to reduce this quantity in night corridor, bedroom, etc. As people is more alert with certain wavelengths, in offices, lighting will be designed to increase worker performances. Rehab Basel, Herzog & De Meuron, Basel, Switserland, 1998-2001 Sources : http://www.rehab.ch/fileadmin/user_upload/Transfer/PDF_allg/RB_Pflegepersonal.pdf (fig 2) http://archrecord.construction.com/projects/bts/archives/healthcare/05_rehab/photos.asp (fig 1 & 3)

5. Effects of light on humans Architecture of Richard Neutra Christopher S. Pechacek, Marilyne Andersen, Steven W. Lockley, Preliminary Method for Prospective Analysis of the Circadian Efficacy of (Day)Light with Applications to Healthcare Architecture, LEUKOS - The Journal of the Illuminating Engineering Society of North America, vol 5 (1), pp. 1-26, July 2008. Mohamed Boubekri, Daylighting, Architecture and Health Building Design Strategies, Architectural Press, 2008. Boyce P.R., Human factors in lighting, 2nd edition, Lighting Research Center, 2003. Steven W. Lockley, Circadian photoreception in humans: More than meets the eye, 3rd VELUX Daylight Symposium in Rotterdam, 13-14 May 2009. Presentation available on http://www.thedaylightsite.com/presentations_s.asp?tp=1022&catid=26&y=2009 Marilyne Andersen, Prospective design implications of recent findings in photobiology, 3rd VELUX Daylight Symposium in Rotterdam, 13-14 May 2009. Presentation available on http://www.thedaylightsite.com/presentations_s.asp?tp=1022&catid=26&y=2009