Category: Uncategorized

Fotoreception study

Educational materials of VŠCHT

Biofyzika – Ústav fyziky a měřicí techniky, VŠCHT PRAHA


I v oku jsou molekulární akceptory energie – pigmenty. Příjem a zpracování informace o
vnějším světě označujeme jako vidění. Zprostředkovávají nám ho fotony viditelného světla
(elektromagnetické záření o λ = 380-780 nm). Jedná se o fyzikálně-fyziologicko-psychologický
proces, zpracovávaný zrakovým analyzátorem – okem, v němž obraz vnějšího světa
vzniká optickou a fotochemickou cestou. K tomu abychom tento obraz vnímali, je informace
z oka přenášena nervovými buňkami (optickými drahami) do zrakového centra mozku, kde
jsou akční potenciály zpracovány.


Celou studii si můžete přečíst zde.


Meeting Report: The Role of Environmental Lighting and Circadian Disruption in Cancer and Other Diseases

2007 study

Richard G. Stevens, David E. Blask, George C. Brainard, Johnni Hansen, Steven W. Lockley, Ignacio Provencio, Mark S. Rea, Leslie Reinlib


Light, including artificial light, has a range of effects on human physiology and behavior and can therefore alter human physiology when inappropriately timed. One example of potential light-induced disruption is the effect of light on circadian organization, including the production of several hormone rhythms. Changes in light–dark exposure (e.g., by nonday occupation or transmeridian travel) shift the timing of the circadian system such that internal rhythms can become desynchronized from both the external environment and internally with each other, impairing our ability to sleep and wake at the appropriate times and compromising physiologic and metabolic processes. Light can also have direct acute effects on neuroendocrine systems, for example, in suppressing melatonin synthesis or elevating cortisol production that may have untoward long-term consequences. For these reasons, the National Institute of Environmental Health Sciences convened a workshop of a diverse group of scientists to consider how best to conduct research on possible connections between lighting and health. According to the participants in the workshop, there are three broad areas of research effort that need to be addressed. First are the basic biophysical and molecular genetic mechanisms for phototransduction for circadian, neuroendocrine, and neurobehavioral regulation. Second are the possible physiologic consequences of disrupting these circadian regulatory processes such as on hormone production, particularly melatonin, and normal and neoplastic tissue growth dynamics. Third are effects of light-induced physiologic disruption on disease occurrence and prognosis, and how prevention and treatment could be improved by application of this knowledge.

Humans have evolved over millions of years and adapted to a solar day of approximately 12 hr of light and 12 hr of dark, latitude and season permitting. Our ability to artificially light the night began about 250,000 years ago when we discovered how to use fire. Candles were introduced about 5,000 years ago, and gas street lighting was possible beginning in the mid-1700s. However, only in the last 120 years has environmental illumination begun to change on a pervasive scale for the masses of people through the introduction of electric lighting. One of the defining features of the built environment in the modern world is this artificial lighting. Electricity has made it possible to light the inside of large buildings and light the night for work, recreation, and security. The benefits of this lighting are obvious and enormous. It has become apparent, however, that although of obvious benefit, it may not be completely innocuous.

Keywords: breast cancer, circadian rhythms, clock genes, lighting, melatonin, phototransduction, pineal gland



One of the defining characteristics of life in the modern world is the altered patterns of light and dark in the built environment made possible by use of electric power. A rapidly growing and very exciting body of basic science is uncovering the mechanisms for phototransduction in the retina for environmental control of circadian and other neurobehavioral responses and the makeup and functioning of the clock physiology that exert genetic control of the endogenous rhythms. It is beginning to be realized by the larger scientific community that maintenance of these circadian rhythms is important to health and well-being. Our challenge for the future is to integrate the basic science with studies in experimental animals and clinical and epidemiologic research to advance our understanding of the impact of circadian disruption from lighting, and what then can be done to minimize or eliminate the adverse consequences for human health.
The entire study can be read on this page.

International Dark-Sky Association – Visibility, Environmental, and Astronomical Issues Associated with Blue-Rich White Outdoor Lighting

2010 study

International Dark-Sky Association

Outdoor lighting is undergoing a substantial change toward increased use of white lighting sources, accelerated most recently by developments in solid-state lighting. Though the perceived advantages of this shift (better color rendition, increased “visual effectiveness” and efficiency, decreased overall costs, better market acceptance) are commonly touted, there has been little discussion of documented or potential environmental impacts arising from the change in spectral energy distribution of such light sources as compared to the high-pressure sodium technology currently used for most area lighting. This paper summarizes atmospheric, visual, health, and environmental research into spectral effects of lighting at night. The physics describing the interaction of light with the atmosphere is long-established science and shows that the increased blue light emission from white lighting sources will increase visible sky glow and detrimental effects on astronomical research through increased scotopic sensitivity and scattering.
Though other fields of study are less mature, there is nonetheless strong evidence for additional potential negative impacts. Vision science, much of it the same research being used to promote the switch to white light sources, shows that such lighting also increases the likelihood of glare and interferes with the ability of the eye to adapt to low light levels a particular concern for older people. Most of the research evidence concerning adverse
effects of lighting on human health concerns circadian rhythm disruptions and breast cancer. The blue portion of the spectrum is known to interfere most strongly with the human endocrine system mediated by photoperiod, leading to reduction in the production of melatonin, a hormone shown to suppress breast cancer growth and development. A direct connection has not yet been made to outdoor lighting, nor particularly to incidental
exposure (such as through bedroom windows) or the blue component of outdoor lighting, but the potential link is clearly delineated. Concerning effects on other living species, little research has examined spectral issues; yet where spectral issues have been examined, the blue component is more commonly indicated to have particular impacts than other colors (e.g., on sea turtles and insects). Much more research is needed before
firm conclusions can be drawn in many areas, but the evidence is strong enough to suggest a cautious approach and further research before a widespread change to white lighting gets underway.

The entire study can be found at this link.

New York Times article: In Eyes, a Clock Calibrated by Wavelengths of Light

2011 article

Laura Beil - The New York Times

In Eyes, a Clock Calibrated by Wavelengths of Light

Just as the ear has two purposes — hearing and telling you which way is up — so does the eye. It receives the input necessary for vision, but the retina also houses a network of sensors that detect the rise and fall of daylight. With light, the body sets its internal clock to a 24-hour cycle regulating an estimated 10 percent of our genes.

The workhorse of this system is the light-sensitive hormone melatonin, which is produced by the body every evening and during the night. Melatonin promotes sleep and alerts a variety of biological processes to the approximate hour of the day.

Light hitting the retina suppresses the production of melatonin — and there lies the rub. In this modern world, our eyes are flooded with light well after dusk, contrary to our evolutionary programming. Scientists are just beginning to understand the potential health consequences. The disruption of circadian cycles may not just be shortchanging our sleep, they have found, but also contributing to a host of diseases.

“Light works as if it’s a drug, except it’s not a drug at all,” said George Brainard, a neurologist at Thomas Jefferson University in Philadelphia and one of the first researchers to study light’s effects on the body’s hormones and circadian rhythms.

Any sort of light can suppress melatonin, but recent experiments have raised novel questions about one type in particular: the blue wavelengths produced by many kinds of energy-efficient light bulbs and electronic gadgets.

Dr. Brainard and other researchers have found that light composed of blue wavelengths slows the release of melatonin with particular effectiveness. Until recently, though, few studies had directly examined how blue-emitting electronics might affect the brain.

So scientists at the University of Basel in Switzerland tried a simple experiment: They asked 13 men to sit before a computer each evening for two weeks before going to bed.

During one week, for five hours every night, the volunteers sat before an old-style fluorescent monitor emitting light composed of several colors from the visible spectrum, though very little blue. Another week, the men sat at screens backlighted by light-emitting diodes, or LEDs. This screen was twice as blue.

Full article can be found at this link.

Light-induced melatonin suppression in humans with polychromatic and monochromatic light.

2007 study

Faculty of Health and Medical Sciences, Human Chronobiology Group, University of Surrey, Guildford, Surrey, UK

The relative contribution of rods, cones, and melanopsin to non-image-forming (NIF) responses under light conditions differing in irradiance, duration, and spectral composition remains to be determined in humans. NIF responses to a polychromatic light source may be very different to that predicted from the published human action spectra data, which have utilized narrow band monochromatic light and demonstrated short wavelength sensitivity. To test the hypothesis that only melanopsin is driving NIF responses in humans, monochromatic blue light (lambda(max) 479 nm) was matched with polychromatic white light for total melanopsin-stimulating photons at three light intensities. The ability of these light conditions to suppress nocturnal melatonin production was assessed. A within-subject crossover design was used to investigate the suppressive effect of nocturnal light on melatonin production in a group of diurnally active young male subjects aged 18-35 yrs (24.9+/-3.8 yrs; mean+/-SD; n=11). A 30 min light pulse, individually timed to occur on the rising phase of the melatonin rhythm, was administered between 23:30 and 01:30 h. Regularly timed blood samples were taken for measurement of plasma melatonin. Repeated measures two-way ANOVA, with irradiance and light condition as factors, was used for statistical analysis (n=9 analyzed). There was a significant effect of both light intensity (p<0.001) and light condition (p<0.01). Polychromatic light was more effective at suppressing nocturnal melatonin than monochromatic blue light matched for melanopsin stimulation, implying that the melatonin suppression response is not solely driven by melanopsin. The findings suggest a stimulatory effect of the additional wavelengths of light present in the polychromatic light, which could be mediated via the stimulation of cone photopigments and/or melanopsin regeneration. The results of this study may be relevant to designing the spectral composition of polychromatic lights for use in the home and workplace, as well as in the treatment of circadian rhythm disorders.
The study can be found at this link.

Green Light Affects Circadian Rhythm

2010 article

Harvard Medical School division of Sleep Medicine

Researchers show that green light is effective in eliciting non-visual responses to light such as resetting circadian rhythms, affecting melatonin production and alerting the brain.

Boston, MA – It has been previously shown that blue light plays an important role in impacting the body’s natural internal body clock and the release of hormones such as melatonin, which is connected to sleepiness, by affecting photoreceptors in specialized cells in the eye.  In new research from Brigham and Women’s Hospital (BWH), researchers have found that green light also plays a role in influencing these non-visual responses. This research is published in the May 12 issue of Science Translational Medicine.

“Over the past decade there have been many non-FDA approved devices and technologies marketed for using blue light therapeutically such as blue light boxes for treatment of Seasonal Affective Disorder and circadian rhythm sleep disorders, and glasses that block blue light from reaching the eye,” said Steven Lockley, PhD, a researcher in the Division of Sleep Medicine at BWH and senior author of the paper. “Our results suggest that we have to consider not only blue light when predicting the effects of light on our circadian rhythms, hormones and alertness, but also other visible wavelengths such as green light.”

The entire article can be read at this link.


Know your sleep cycle, and use it.

2014 article


We are all subject to a sleep cycle of about 90 minutes duration. In that period, we go from light sleep to deep sleep and back when we are asleep; or we go from feeling tired to being alert and becoming tired again, when we are awake.

Use your sleep cycle by noting when you wake up in the morning, without the use of an alarm clock. You’ll notice that if you wake up unaided by an alarm at 06.00 and then go to sleep, the next time you’ll wake up, is around 07.30. If you also woke up earlier, for instance from a dream, that would be around 04.30.

These are your awake-times in the morning. But most people calculate the time they need to get to work, and count backwards to the time they set their alarm – often ensuring that they wake up between their awake-times, when their bodies are in deep sleep. Instead of waking up fresh, you stagger out of bed like a zombie.

The entire article can be read at this link.

How artificial light is wrecking your sleep, and what to do about it

2013 article

Source Chris Kresser

“A good laugh and a long sleep are the best cures in the doctor’s book.” – Irish Proverb

The evidence for the health benefits of adequate, restful sleep is overwhelming. Decades of research has shown that sleeping between 7 and 9 hours per night can relieve stress, reduce the risk of many chronic diseases, improve memory and cognitive function, and may even help with weight loss. As many of us know by now, getting adequate, high-quality sleep is one of the most important, yet under-appreciated steps you can take to improve your overall health and wellbeing.

Read more at this link.

Non-visual effects of light on melatonin, alertness and cognitive performance: can blue-enriched light keep us alert?

2011 study

Chellappa SL  Centre for Chronobiology, Psychiatric Hospital of the University of Basel, Basel, Switzerland
Steiner R, Blattner P, Oelhafen P, Götz T, Cajochen C,


Light exposure can cascade numerous effects on the human circadian process via the non-imaging forming system, whose spectral relevance is highest in the short-wavelength range. Here we investigated if commercially available compact fluorescent lamps with different colour temperatures can impact on alertness and cognitive performance.


Sixteen healthy young men were studied in a balanced cross-over design with light exposure of 3 different light settings (compact fluorescent lamps with light of 40 lux at 6500K and at 2500K and incandescent lamps of 40 lux at 3000K) during 2 h in the evening.


Exposure to light at 6500K induced greater melatonin suppression, together with enhanced subjective alertness, well-being and visual comfort. With respect to cognitive performance, light at 6500K led to significantly faster reaction times in tasks associated with sustained attention (Psychomotor Vigilance and GO/NOGO Task), but not in tasks associated with executive function (Paced Visual Serial Addition Task). This cognitive improvement was strongly related with attenuated salivary melatonin levels, particularly for the light condition at 6500K.


Our findings suggest that the sensitivity of the human alerting and cognitive response to polychromatic light at levels as low as 40 lux, is blue-shifted relative to the three-cone visual photopic system. Thus, the selection of commercially available compact fluorescent lights with different colour temperatures significantly impacts on circadian physiology and cognitive performance at home and in the workplace.

The study can be found at this link

Blue-enriched white light in the workplace improves self-reported alertness, performance and sleep quality.

2088 study

Viola AU, Surrey Sleep Research Centre, Clinical Research Centre, Egerton Road, Guildford, United Kingdom
James LM, Schlangen LJ, Dijk DJ


Specifications and standards for lighting installations in occupational settings are based on the spectral sensitivity of the classical visual system and do not take into account the recently discovered melanopsin-based, blue-light-sensitive photoreceptive system. The authors investigated the effects of exposure to blue-enriched white light during daytime workhours in an office setting.


The experiment was conducted on 104 white-collar workers on two office floors. After baseline assessments under existing lighting conditions, every participant was exposed to two new lighting conditions, each lasting 4 weeks. One consisted of blue-enriched white light (17 000 K) and the other of white light (4000 K). The order was balanced between the floors. Questionnaire and rating scales were used to assess alertness, mood, sleep quality, performance, mental effort, headache and eye strain, and mood throughout the 8-week intervention.


Altogether 94 participants [mean age 36.4 (SD 10.2) years] were included in the analysis. Compared with white light (4000 K), blue-enriched white light (17 000 K) improved the subjective measures of alertness (P<0.0001), positive mood (P=0.0001), performance (P<0.0001), evening fatigue (P=0.0001), irritability (P=0.004), concentration (P<0.0001), and eye discomfort (P=0.002). Daytime sleepiness was reduced (P=0.0001), and the quality of subjective nocturnal sleep (P=0.016) was improved under blue-enriched white light. When the participants‘ expectation about the effect of the light treatments was entered into the analysis as a covariate, significant effects persisted for performance, alertness, evening fatigue, irritability, difficulty focusing, concentrating, and blurred vision.


Exposure to blue-enriched white light during daytime workhours improves subjective alertness, performance, and evening fatigue.

The study can be found at this link.