Beyond our eyes: the non-visual impact of light Christian Cajochen, PhD Centre for Chronobiology Psychiatric Hospital of the University of Basel, Switzerland Workshop Intelligent Efficient Human Centric Lighting Muttenz/Basel 12.. December 2016
Thomas Edison was maybe wrong!
Light is the most important Zeitgeber! Buttgereit, Smolen, Coogan, Cajochen, Nat Rev Rheumatol, 2015
Plasma Melatonin (pmol/l) Light and human circadian rhythms Melatonin as the best circadian marker in humans Induction of a Phase Delay in the Human Circadian Melatonin Rhythm by Light (10 000 lux for 6.5 h) Midpoint 4:45 Midpoint 8:21 400 Light 300 200 100 0 12 24 12 24 12 24 12 24 12 Time of Day Sleep period Khalsa et al., J Physiol (London) 2003
Phase shift (h) Light and circadian phase Phase-Response Curve 4 3 2 1 0-1 -2-3 -4-18 -15-12 -9-6 -3 0 3 6 9 12 15 18 Initial Phase (time relative to DLMO=0) 6.7 hours 10 000 lux polychromatic white Retina light Khalsa, et al., J Physiol (London) 2003
«Light impacts on our circadian rhythms more powerfully than any drug» Charles Czeisler «Casting light on sleep deficiency» Nature, 2013
Suppression of melatonin in a totally blind person with bright light 300 Sighted Person 200 100 Plasma Melatonin (pmol/liter) 37.5 37.0 36.5 Core Body Temperature ( C) 36.0 300 12 18 24 6 12 18 24 6 12 Time of Day (h) Blind Person 200 100 Plasma Melatonin (pmol/liter) 37.5 37.0 36.5 36.0 12 18 24 6 12 18 24 6 12 Time of Day (h) Core Body Temperature ( C) Czeisler et al., New Engl Med 1995
Correct Answer (%) Light is more than vision non-visual / non-image forming light effects Light can be «seen» without conscious vision «Forced choice» test in a totally blind person 100 * 80 60 40 20 0 420 460 481 500 506 515 540 560 580 Wavelength (nm) Nach Zaidi et al., Curr Biol, 2007
Non-classical Photoreceptor intrinsic photosensitive retinal ganglion cells (iprgs, Melanopsin) SCN (circadian Pacemaker) Eye A dual sensory organ Rods Retina Cones Hattar et al. Science, 2002 Berson et al. Science, 2002
Phase shift (h) Light and circadian phase Phase-Response Curve 4 3 2 1 0-1 -2-3 -4-18 -15-12 -9-6 -3 0 3 6 9 12 15 18 Initial Phase (time relative to DLMO=0) 75 % of the resetting response 6.7 hours 10 000 lux polychromatic white Retina light 6.5 hours blue light (480 nm) 11.8 μwcm 2, 11.2 lux) Khalsa, et al., J Physiol (London) 2003 Rüger, et al., J Physiol (London) 2013
Relative Contribution Relative Contribution Why is this relevant: Light bulb versus LED Wavelength (nm) Wavelength (nm)
Smartphone use in adolescents (14-20 years) Use of smartphones 1 hour prior bedtime Where do you keep your smartphone during night? 99 % Ja nicht beantwortet 23% 14% irgendwo in der Wohnung irgendwo im Zimmer auf dem Nachttisch 99% yes 60% im Bett nicht beantwortet 97% in bedroom How often do you use your smartphone after «Lights off» 49% 10% 25% 15% nie selten gelegentlich häufig nicht beantwortet Strube et al. Somnologie, 2016 74% occasionally-often
Light has also «non-circadian» acute effects Light suppresses the soporific hormone melatonin within minutes (Gronfier et al., 2002) Light inhibits sleep-promoting GABA neurons in the ventrolateral preoptic area in the hypothalamus (VLPO, Tsai et al., 2009) Light activates wake-promoting orexin neurons in the lateral hypothalamus (McGregor et al., 2011)
Sleep Response (min) Acute sleep induction by light in nocturnal mice 60 Lights ON Lights OFF Wildtype Melanopsin knockout 30 Melanopsin adta 0 0 1 2 3 Time elapsed from light onset (h) According to Muindi et al., Front Syst Neurosci, 2014
more alert Acute alerting effects of light in diurnal humans Subjective Alertness 5 10 15 20 120 lux! 25 10 100 1000 10000 Illuminance (lux) Cajochen et al., Beh Brain Res. 2000
Karolinska Sleepiness Scale (KSS) % Sleepiness Change 0 = pre-light Karolinska Sleepiness Scale (KSS) The human alerting response to light is blue-shifted Monochromatic light Energy Saving Lamps Computer Screens 50 8 6 40 7 30 20 5 6 10 0 4 Cajochen et al., Sleepiness and human impact assessment Book chapter, Springer, 2014
slower Relative Reaction Time (%) faster Baseline Dark Adaptation Sustained Attention and Response Control (Go/noGo Task) Letter W : go Letter M : no-go 90 95 LED Screen 100 105 Non-LED Screen Monitor: F 1,11 =12.2; p<0.04 Time of day: F 11,44 =7.8; p<0.02 Monitor x Time: F 12,132 =3.0; p=0.041 110 18:15 19:15 20:15 21:15 22:15 23:15 00:15 Time of Day (h) * * * P <0.05 Cajochen et al., J Appl Physiol. 2011
% Declarative Learning (Word pairs) Correctly identified old word pairs Correctly identified new word pairs 70 65 70 65 * 60 60 55 55 50 50 45 45 LED Screen Non-LED * P <0.05 Cajochen et al., J Appl Physiol. 2011
Light is not just for vision Cortex Thalamus Hypothalamus Brainstem - Locus coeruleus Limbic system - Amygdala - Hippocampus Modified from Vandewalle et al. Trends Cogn Sci, 2009
Light has many non-visual biological effects in humans (only peer reviewed data) Synchronization of circadian rhythms Suppression of the «darkness hormone» melatonin Alerting and enhancing of cognitive performance Regulation of pupil size Enhancing mood (antidepressant) Enhancing physical performance in top athletes Light color modulates mental effort
Conclusion Light rules our body via its non-visual effects Blue wavelengths -- which are beneficial during daylight hours because they boost attention, reaction times, mood, and physical performance -- are most disruptive at night The proliferation of electronics with screens, as well as energy-efficient lighting, is increasing our exposure to blue wavelengths, especially after sundown
Non-visual lighting solutions should be: Dynamic Intensity and duration Spectral composition According to time of day Individual Age Gender Chronotype (early vs.late people)
Wanted Intelligent human centric lighting to adapt our illuminated surroundings such that we do not jeopardize quality of life and health but positively influence our sleep, circadian physiology, cognition and well-being Human Centric Lighting the room by enter Human centric lighting supports your health and promotes
Centre for Chronobiology Acknowledgements www.chronobiology.ch Antoine Viola, PhD Christina Schmidt, PhD Mirjam Münch, PhD Sarah Chellappa, PhD Vivien Bromundt, PhD Jakub Späti, PhD Sylvia Frey, PhD Virginie Gabel Micheline Maire Carolin Reichert Stephanie van der Lely Swiss Federal Office for Public Health Daimler-Benz Foundation EU IP