• Light is an electromagnetic radiation of various wavelengths. Long wavelengths are red, the short ones are blue.
    Blue light is harmful during the night.

    The Basics


    This light of more than 4000 K, also known as neutral/cold white light, is the richest in blue wavelengths of 450-480 nanometers, yet it does not appear blue. It aids us in concentrating during the day hence is ideal for use during work or school. It is important to note that other commonly used warmer lights also contain blue wavelengths but of lower levels.



    Cell phones, tablets, computer screens, TV and electronic visual displays as such emit high amounts of blue wavelengths. As a consequence, they should be avoided 90 minutes before sleep or, alternatively, used with screens or eyewear with red filters that block blue wavelengths during this time.


    We should avoid being exposed to blue wavelengths prior to sleep to maintain proper melatonin secretion. It is suggested to avoid being exposed to blue wavelengths 90 minutes before sleep or, alternatively, 9.5 hours before waking up.

    If electronics with visual display screen need to be used during this time, using screen foils or eyewear with a red filters is necessary as the light's blue wavelengths will be filtered and hence will not reach our eyes.


    Light during the day is rich in all wavelengths including blue, however as the sun begins to set, blue wavelengths are filtered-out and the light is rich in red wavelengths – this is why we see the sun orange-red during sunset. The absence of blue wavelengths triggers the secretion of melatonin.


    Melatonin is a hormone that controls the daily night-day cycle, thereby allowing the entrainment of circadian rhythms. Simply, it makes us want to sleep, but not only that: it is also a powerful antioxidant and is believed to play a vital role in the immune system. Its secretion is inhibited by light's blue wavelengths and, conversely, is stimulated in the absence of these wavelengths. Melatonin plays a role of utmost importance in proper sleep and its decreased levels over longer periods of time lead to serious health problems, possibly including cancer as recent research suggests.

    The most underestimated health hazard is nocturnal light.

    Spectrometer measurements

    Studies & Articles

    „Melatonin’s role in Cancer“ Talk By Russel J. Reiter, PhD

    Pupillary reflex to red light and white light

    Red monochromatic light going through the eye pupil in the range of 610-760nm causes no pupillary constriction. Hitting eye pupil 7438K CCT white light with peak in blue 444nm causes a rapid contraction of the pupil.

    Narrowing and broadening of the pupil is the job of ganglion cells. Besides other functions, their sensitivity is the strongest in the 460-480nm range. On monochromatic red light more than 600nm, ganglion cells do not respond as well as rhodopsin in rods.

    Study by George C. Brainarda

    2001 study

    Action Spectrum for Melatonin Regulation in Humans: Evidence for a Novel Circadian Photoreceptor

    George C. Brainard,John P. Hanifin,Jeffrey M. Greenson, Brenda Byrne, Gena Glickman, Edward Gerner, a Mark D. Rollag
    Department of Neurology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, and 2Department of Anatomy, Physiology and Genetics, Uniformed Services University of Health Sciences, Bethesda, Maryland 20814

    The photopigment in the human eye that transduces light for circadian and neuroendocrine regulation, is unknown. The aim of this study was to establish an action spectrum for lightinduced melatonin suppression that could help elucidate the ocular photoreceptor system for regulating the human pineal gland. Subjects (37 females, 35 males, mean age of 24.5  0.3 years) were healthy and had normal color vision. Full-field, monochromatic light exposures took place between 2:00 and 3:30 A.M. while subjects’ pupils were dilated. Blood samples collected before and after light exposures were quantified for melatonin. Each subject was tested with at least seven different irradiances of one wavelength with a minimum of 1 week between each nighttime exposure. Nighttime melatonin suppression tests (n 627) were completed with wavelengths from 420 to 600 nm. The data were fit to eight univariant, sigmoidal fluence–response curves (R2 0.81–0.95). The action spectrum constructed from these data fit an opsin template (R2 0.91), which identifies 446–477 nm as the most potent wavelength region providing circadian input for regulating melatonin secretion. The results suggest that, in humans, a single photopigment may be primarily responsible for melatonin suppression, and its peak absorbance appears to be distinct from that of rod and cone cell photopigments for vision. The data also suggest that this new photopigment is retinaldehyde based. These findings suggest that there is a novel opsin photopigment in the human eye that mediates circadian photoreception.

    Key words: melatonin; action spectrum; circadian; wavelength; light; pineal gland; neuroendocrine; photoreception; photopigment; human




    The action spectrum presented here matches a vitamin A1- retinaldehyde photopigment template that supports the hypothesis that one of the new opsin photopigment candidates provides primary photic input for melatonin regulation in humans. The molecular identification of candidate opsin or non-opsin photoreceptors and their localization in the retina and/or neural components of the circadian system make them well suited to act as circadian phototransducers. However, functional data confirming any of these molecules as having a direct role in mammalian circadian photoreception is currently lacking. Furthermore, caution should be exercised in generalizing results from plants, insects, fish, amphibians, and rodents to humans. Are the effects of light on melatonin suppression relevant to general circadian regulation? Studies have shown that hamsters have a higher intensity threshold for light-induced phase-shifts of wheel-running rhythms than for melatonin suppression (Nelson and Takahashi, 1991). Recently, however, a study on humans showed that the 50% response sensitivity for circadian phase shifting (119 lux) was only slightly higher than that for melatonin suppression (106 lux) with white light (Zeitzer et al., 2000). It is possible that there are separate photoreceptors for mediating circadian entrainment versus acute suppression of melatonin. It is reasonable, however, to hypothesize that a variety of nonvisual effects of light, such as melatonin suppression, entrainment of circadian rhythms, and possibly some clinical responses to light, are mediated by a shared photoreceptor system. Additional experiments are needed to test this hypothesis. In general, relatively high light illuminances ranging from 2500 to 12,000 lux are used for treating winter depression, selected sleep disorders, and circadian disruption (Wetterberg, 1993; Lam, 1998). Although these light levels are therapeutically effective, some patients complain that they produce side effects of visual glare, visual fatigue, photophobia, ocular discomfort, and headache. Determining the action spectrum for circadian regulation may lead to improvements in light therapy. Total illuminances for treating a given disorder can be reduced as the wavelength emissions of the therapeutic equipment are optimized. Modern industrialized societies use light extensively in homes, schools, work places, and public facilities to support visual performance, visual comfort, and aesthetic appreciation within the environment. Given that light is also a powerful regulator of the human circadian system, future lighting strategies will need to provide illumination for human visual responses, as well as homeostatic responses. The action spectrum presented here suggests that there are separate photoreceptors for visual and circadian responses to light in humans. Hence, new approaches to architectural lighting may be needed to optimally stimulate both the visual and circadian systems. In conclusion, this study characterizes the wavelength sensitivity of the ocular photoreceptor system for regulating the human pineal gland by establishing an action spectrum for light-induced melatonin suppression. The results identify the 446–477 nm portion of the spectrum as the most potent wavelengths providing circadian input for regulating melatonin secretion. These data suggest that the primary photoreceptor system for melatonin suppression is distinct from the rod and cone photoreceptors for vision. Finally, this action spectrum suggests that there is a novel retinaldehyde photopigment that mediates human circadian photoreception. These findings open the door for optimizing the use of light in both therapeutic and architectural applications


    Whole study of the impact of light on the suppression of melatonin secretion can be read here

    Effects of LED-backlit Computer Screen and Emotional Selfregulation on Human Melatonin Production

    35th Annual International Conference of the IEEE EMBS  2013

    Watchara Sroykham, Student Member, IEEE and Yodchanan Wongsawat, Member, IEEE

    Abstract— Melatonin is a circadian hormone transmitted via suprachiasmatic nucleus (SCN) in the hypothalamus and sympathetic nervous system to the pineal gland. It is a hormone necessary to many human functions such as immune, cardiovascular, neuron and sleep/awake functions. Since melatonin enhancement or suppression is reported to be closely related to the photic information from retina, in this paper, we aim further to study both the lighting condition and the emotional self-regulation in different lighting conditions together with their effects on the production of human melatonin. In this experiment, five participants are in three light exposure conditions by LED backlit computer screen (No light, Red light (~650nm) and Blue light (~470nm)) for 30 minute (8-8:30pm), then they are collected saliva both before and after the experiments. After the experiment, the participants are also asked to answer the emotional selfregulation questionnaire of PANAS and BRUMS regarding each light exposure condition. These results show that positive mood mean difference of PANAS between no light and red light is significant with p=0.001. Tension, depression, fatigue, confusion and vigor from BRUMS are not significantly changed while we can observe the significant change in anger mood. Finally, we can also report that the blue light of LEDbacklit computer screen significantly suppress melatonin production (91%) more than red light (78%) and no light (44%).

    I. INTRODUCTION Melatonin or N-Acetyl-5-methoxytryptamine is a circadian hormone. It is rhythmically produced by the pineal grand in the brain with a low level during daytime and a high level during nighttime. The level of melatonin rises during the evening (8-11pm). It will reach the peak level between 2- 4am and decrease to the baseline level during late morning (8-10am). This mechanism is controlled by the suprachiasmatic nucleus (SCN) which is inhibited by light and is stimulated by darkness. Melatonin is also known as a hormone necessary to many human functions such as immune, cardiovascular, neuron and sleep/awake functions. In recent, technology development has led to energysaving and effective electronic devices. The Light-Emitting Diode (LED) is one of those. It is widely used in display of This project is supported in part by the government funding of Mahidol University. W. Sroykham is with the Department of Biomedical Engineering, Mahidol University, 25/25 Putttamonthon 4, Salaya, Nakornpathom 73170 Thailand and with Center for Biomedical Instrument Research and Development, Institute of Molecular Biosciences,Mahidol University, 25/25 Putttamonthon 4, Salaya, Nakornpathom 73170 Thailand(e-mail: watchara.sro@mahidol.ac.th). Y. Wongsawat is with the Department of Biomedical Engineering, Mahidol University, 25/25 Putttamonthon 4, Salaya, Nakornpathom 73170 Thailand (corresponding author, phone: 66-82-889-2138 Ext 6361; fax: 66- 82-889-2138 Ext 6366; e-mail: yodchanan.won@mahidol.ac.th). electronic device such as smart mobile phone, television, desktop computer, notebook computer and tablet. However, the light form this device can suppress human melatonin production. Recently Studies, Wood et al (2013) showed that melatonin production can be suppressed after 1-2 hours by tablet with blue LEDs [1]. Cajochen et al (2011) showed that LED-backlit computer screen can significantly suppressed human melatonin production more than a non-LED backlit computer screen [2]. Furthermore, Figueiro et al (2011) showed that light from cathode ray tube computer screen can slightly suppressed human melatonin production and has suggested that the light from electrical devices at nighttime can suppress human melatonin production [3]. Lewy et al also showed that melatonin secretion in human can be suppressed by artificial light [4].

    whole study here

    Illuminating the deleterious effects of light at night

    2011 study

    Laura K. Fonken, Randy J. Nelson
    Department of Neuroscience and The Institute for Behavioral Medicine Research, The Ohio State University

    Technological advances, while providing many benefits, often create circumstances that differ from the conditions in which we evolved. With the wide-spread adoption of electrical lighting during the 20thcentury, humans became exposed to bright and unnatural light at night for the first time in their evolutionary history. Electrical lighting has led to the wide-scale practice of 24-hour shift-work and has meant that what were once just “daytime” activities now run throughout the night; in many ways Western society now functions on a 24-hour schedule. Recent research suggests that this gain in freedom to function throughout the night may also come with significant repercussions. Disruption of our naturally evolved light and dark cycles can result in a wide range of physiological and behavioral changes with potentially serious medical implications. In this article we will discuss several mechanisms through which light at night may exert its effects on cancer, mood, and obesity, as well as potential ways to ameliorate the impact of light at night.

    At different times during our respective childhoods, we both toured Carlsbad Caverns in New Mexico. As part of the tour, the lights in the cave were turned off. The darkness was incredible, engulfing absolutely everything. In our society, we rarely experience such profound darkness; every night, our homes, work places, and streets are brightly illuminated by the glow of electric lights. We will of course always be naturally illuminated by the stars and the moon on a clear night, but we can safely say that most of the light we experience at night is unnatural.

    Humans are diurnal, that is, we evolved to be active during the day and to sleep at night. As such, we never developed the ability to see well in the dark. Over time, we have, however, developed the desire to do more and more during the time we are awake, be it night or day, and so we have created an environment that corrects for our relative night blindness. Since the advent of electrical lighting around the turn of the 20thcentury, humans have become increasingly exposed to bright and unnatural light at night. Urban development has further exacerbated the issue, with lighting from infrastructure straying into the atmosphere nightly (Figure 1). Today, 99% of the population in the United States and Europe, and 62% of the world’s remaining population, are exposed to this “light pollution” [1]. There is no denying that the invention of electrical lighting was a boon for developing industry and technology, allowing the extension of the workday into the night and boosting economic development. However, the use of light at night continues to rapidly increase (by 6% per year) [1] without thorough (or any) consideration of its biological implications.




    A common risk factor in many of the pathologies associated with exposure to light at night is a change in immune function, notably inflammatory responses, and recent research has demonstrated that light at night may detrimentally affect the immune system [18]. Thus, in addition to investigating the influence of melatonin and circadian disruption as mechanisms contributing to the maladaptive affects of light at night, characterization of the inflammatory response is also warranted.

    One important population that is often neglected when considering light at night is patients in hospitals. While multiple epidemiological studies have been conducted on nurses, there are no studies on the impact of light at night on the patients with whom they work. Many in-patients are already at high risk of increased inflammation and disrupted physiology, which may be exacerbated by light at night.

    Preventing the general population from excessive exposure to light at night can be achieved with relatively low-cost manipulations, such as using curtains to block out street lights, turning off hallway lights, and removing all light sources, including televisions and computers, from bedrooms. However, these methods do not prevent the extension of daytime hours that many of us experience, but by no means do we recommend that everyone go to bed at sunset. Rather, it may be important for people to try to keep a consistent schedule and avoid rapid shifts in their waking hours. This is often unavoidable in shift-working populations, and there are ongoing studies currently comparing visual aids that may alleviate some of the maladaptive effects of exposure to light at night in shift workers. More specifically, not all lighting has an equal effect; the intrinsically photosensitive retinal ganglion cells that project to the master circadian clock in the brain contain melanopsin and are most responsive to the blue region of the visible spectrum (ranging from 450 to 485 nm), with longer wavelengths of lighting minimally impacting the circadian system. Manipulation of wavelength may prove effective in blocking out some of the light-induced physiological changes. Current research investigating the effectiveness of goggles designed to block out blue wavelength lighting on preventing light-induced melatonin suppression is ongoing. Furthermore, work environments could potentially use lighting sources that emit less blue light, which unfortunately is at odds with the push for energy-saving compact fluorescent bulbs.

    Modern society now functions on a 24-hour schedule. Although there are many economic and other societal benefits to such a schedule, there is converging evidence from epidemiological and experimental work that light at night has unintended, maladaptive consequences. In many ways, this field of study is just beginning; further characterization of the impact of light at night is needed along with effective interventions to ameliorate the unintended negative effects of light at night on health.

    The entire study, the effect of exposure to light at night can be read at this link.

    Circadian and Melatonin Disruption by Exposure to Light at Night Drives Intrinsic Resistance to Tamoxifen Therapy in Breast Cancer

    July 2014 study

    Robert T. Dauchy, Shulin Xiang, Lulu Mao, Samantha Brimer, Melissa A. Wren, Lin Yuan, Muralidharan Anbalagan, Adam Hauch, Tripp Frasch, Brian G. Rowan1, David E. Blask, and Steven M. Hill


    Resistance to endocrine therapy is a major impediment to successful treatment of breast cancer. Preclinical and
    clinical evidence links resistance to antiestrogen drugs in breast cancer cells with the overexpression and/or
    activation of various pro-oncogenic tyrosine kinases. Disruption of circadian rhythms by night shift work or
    disturbed sleep-wake cycles may lead to an increased risk of breast cancer and other diseases. Moreover, light
    exposure at night (LEN) suppresses the nocturnal production of melatonin that inhibits breast cancer growth. In
    this study, we used a rat model of estrogen receptor (ERaþ) MCF-7 tumor xenografts to demonstrate how altering
    light/dark cycles with dim LEN (dLEN) speed the development of breast tumors, increasing their metabolism and
    growth and conferring an intrinsic resistance to tamoxifen therapy. These characteristics were not observed in
    animals in which the circadian melatonin rhythm was not disrupted, or in animals subjected to dLEN if they
    received nocturnal melatonin replacement. Strikingly, our results also showed that melatonin acted both as a tumor
    metabolic inhibitor and a circadian-regulated kinase inhibitor to reestablish the sensitivity of breast tumors to
    tamoxifen and tumor regression. Together, our findings show how dLEN-mediated disturbances in nocturnal
    melatonin production can render tumors insensitive to tamoxifen. Cancer Res; 74(15); 1–12. 2014 AACR.



    Differential effects of 4OH-TAM on the growth and regression of (ERaþ ) MCF-7 tissue-isolated breast tumor xenografts in female nude rats housed in standard lighting schedule (LD 12:12) or in dLEN lighting schedules with or without melatonin supplementation. A, study I, estimated tumor weight (g/d) of MCF-7 (ERaþ) human breast tumor xenografts from nude rats exposed to a dLEN lighting schedule and treated diluent (red triangles) with 4OH-TAM (blue triangles; 80 mg/kg/d) or a LD 12:12 lighting schedule and treated with diluent (black circles) or 4OH-TAM (green circles). B, study II, estimated tumor weight (g/d) of MCF-7 (ERaþ) human breast tumor xenografts from nude rats exposed to a dLEN lighting schedule and treated with vehicle (red triangles) or 4OH-TAM (blue triangles; 80 mg/kg/d) or in a dLEN lighting schedule supplemented with exogenous melatonin at night and treated vehicle (black circles) or 4OH-TAM (green circles). Tumor weights were estimated daily as described in Materials and Methods. Images of tumor-bearing nude rats in studies I (A, i–iv) and II (B, i–iv) maintained on either experimental (dLEN) or control (LD12:12) lighting schedules, as described in Materials and Methods. A, xengografts from experimental animals 28 days after tumor implant in dLEN (i, top) and LD 12:12 (ii). iii and iv, xenografts from experimental animals 40 days after tumor implant in LD 12:12 and diluent treatment (iii) and LD 12:12 after 28 days of treatment with tamoxifen (iv). Photographs in B are xenografts from experimental animals 28 days after tumor implant in control dLEN lighting schedule (i) and dLEN supplemented with exogenous nighttime melatonin (ii). B, iii, xenografts from experimental animals 40 days after tumor implant in dLEN supplemented with exogenous nighttime melatonin and administered the vehicle for tamoxifen. B, iv, xenografts from experimental animals 40 days after tumor implant in dLEN but supplemented with exogenous nighttime melatonin and after treatment with tamoxifen.

    Whole study can be read here.

    Article Harvard Health Publications

    2012 study

    Harvard Health Publications - Harvard Medical School

    Blue light has a dark side

    Light at night is bad for your health, and exposure to blue light emitted by electronics and energy-efficient lightbulbs may be especially so.

    Until the advent of artificial lighting, the sun was the major source of lighting, and people spent their evenings in (relative) darkness. Now, in much of the world, evenings are illuminated, and we take our easy access to all those lumens pretty much for granted.

    But we may be paying a price for basking in all that light. At night, light throws the body’s biological clock—the circadian rhythm—out of whack. Sleep suffers. Worse, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity.

    But not all colors of light have the same effect. Blue wavelengths—which are beneficial during daylight hours because they boost attention, reaction times, and mood—seem to be the most disruptive at night. And the proliferation of electronics with screens, as well as energy-efficient lighting, is increasing our exposure to blue wavelengths, especially after sundown.


    Daily rhythms influenced by light

    Everyone has slightly different circadian rhythms, but the average length is 24 and one-quarter hours. The circadian rhythm of people who stay up late is slightly longer, while the rhythms of earlier birds fall short of 24 hours. Dr. Charles Czeisler of Harvard Medical School showed, in 1981, that daylight keeps a person’s internal clock aligned with the environment.




    Full article on the influence of blue wavelengths of white light on the human body can be read here


    2014 article

    Source en.wikipedia.org

    Melanopsin is a photopigment found in some retinal ganglion cells in the eyes of humans and other vertebrates. These cells, known as intrinsically photosensitive retinal ganglion cells, perceive light but are much slower to react to visual changes than the better-known rod and cone cells. They have been shown to affect circadian rhythms, the pupillary light reflex, and several other functions related to ambient light.

    In structure, melanopsin is an opsin, a retinylidene protein variety of G-protein-coupled receptor. Melanopsin is most sensitive to blue light. A melanopsin based receptor has been linked to the association between light sensitivity and migraine pain.

    Melanopsin differs from other opsin photopigments in vertebrates. In fact, it resembles invertebrate opsins in many respects, including its amino acid sequence and downstream signaling cascade. Like invertebrate opsins, melanopsin appears to be a bistable photopigment, with intrinsic photoisomerase activity, and to signal through a G-protein of the Gq family.



    Evidence supports prior theories that melanopsin is the photopigment responsible for the entrainment of the central „body clock“, the suprachiasmatic nuclei (SCN), in mammals. Fluorescent immunocytochemistry was used to visualize melanopsin distribution throughout the rat retina and showed that melanopsin was found in approximately 2.5% of the total rat retinal ganglion cells (RGCs) and that these cells were indeed ipRGCs. Using β-galactosidase as a marker for the melanopsin gene, X-gal labeling of these ipRGCs showed that their axons directly target the SCN, providing further evidence that melanopsin is important in entrainment through the retinohypothalamic tract (RHT).

    More about melanopsin can be read here.


    2013 article

    Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix                            z webu: University of Meryland Medical Center


    Melatonin is a hormone secreted by the pineal gland in the brain. It helps regulate other hormones and maintains the body’s circadian rhythm. The circadian rhythm is an internal 24-hour “clock” that plays a critical role in when we fall asleep and when we wake up. When it is dark, your body produces more melatonin; when it is light, the production of melatonin drops. Being exposed to bright lights in the evening or too little light during the day can disrupt the body’s normal melatonin cycles. For example, jet lag, shift work, and poor vision can disrupt melatonin cycles.

    Melatonin also helps control the timing and release of female reproductive hormones. It helps determine when a woman starts to menstruate, the frequency and duration of menstrual cycles, and when a woman stops menstruating (menopause).

    Some researchers also believe that melatonin levels may be related to aging. For example, young children have the highest levels of nighttime melatonin. Researchers believe these levels drop as we age. Some people think lower levels of melatonin may explain why some older adults have sleep problems and tend to go to bed and wake up earlier than when they were younger. However, newer research calls this theory into question.

    Melatonin has strong antioxidant effects. Preliminary evidence suggests that it may help strengthen the immune system.




    Studies suggest that melatonin supplements may help people with disrupted circadian rhythms (such as people with jet lag or those who work the night shift) and those with low melatonin levels (such as some seniors and people with schizophrenia) to sleep better. A review of clinical studies suggests that melatonin supplements may help prevent jet lag, particularly in people who cross five or more time zones.


    Breast Cancer

    Prostate Cancer


    Benzodiazepine Withdrawal


    Irritable Bowel Syndrome



    The entire article can be read at this odkaze.

    Intrinsically photosensitive retinal ganglion cells

    2015 article

    Source en.wikipedia.org

    Intrinsically photosensitive Retinal Ganglion Cells (ipRGCs), also called photosensitive Retinal Ganglion Cells (pRGC), or melanopsin-containing retinal ganglion cells, are a type of neuron (nerve cell) in the retina of the mammalian eye. They were discovered in 1923, forgotten, rediscovered in the early 1990s, and are, unlike other retinal ganglion cells, intrinsically photosensitive. This means that they are a third class of retinal photoreceptors, excited by light even when all influences from classical photoreceptors (rods and cones) are blocked (either by applying pharmacological agents or by dissociating the ganglion cell from the retina). Photosensitive ganglion cells contain the photopigment melanopsin. The giant retinal ganglion cells of the primate retina are examples of photosensitive ganglion cells.


    Research in humans

    Attempts were made to hunt down the receptor in humans, but humans posed special challenges and demanded a new model. Unlike in other animals, researchers could not ethically induce rod and cone loss either genetically or with chemicals so as to directly study the ganglion cells. For many years, only inferences could be drawn about the receptor in humans, though these were at times pertinent.

    In 2007, Zaidi and colleagues published their work on rodless, coneless humans, showing that these people retain normal responses to nonvisual effects of light. The identity of the non-rod, non-cone photoreceptor in humans was found to be a ganglion cell in the inner retina as shown previously in rodless, coneless models in some other mammals. The work was done using patients with rare diseases that wiped out classic rod and cone photoreceptor function but preserved ganglion cell function. Despite having no rods or cones, the patients continued to exhibit circadian photoentrainment, circadian behavioural patterns, melatonin suppression, and pupil reactions, with peak spectral sensitivities to environmental and experimental light that match the melanopsin photopigment. Their brains could also associate vision with light of this frequency. Clinicians and scientists are now seeking to understand the new receptor’s role in human diseases and, as discussed below, blindness.

    Full article on retinal ganglion cells can be read here.

    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

    Source witness.theguardian.com

    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 chriskresser.com

    “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.

    Marc Green Phd – Night vision

    2013 article

    Marc Green Phd.

    Night vision is an important factor in understanding the cause of accidents that occur under low visibility. Here, I briefly outline some basics, roughly what I would expect my students to know at the end of an introductory perception course. [See related articles The Invisible Pedestrian and Police Shootings.]

    Photopic, Mesopic and Scotopic Vision

    Humans can see over a light intensity range of several million to one. In order to achieve this extraordinary feat while maintaining good contrast sensitivity, the eye adjusts to the prevailing conditions and changes its mode of operation as light levels decline from day to night.Every beginner’s textbook discusses rods and cones, so amateurs pick up on this these terms and focus too heavily on them. Photoreceptors alone are insufficient to explain night vision. Moreover, rod vision and night vision are not synonymous. The more important concept is „receptive field,“ which is fundamental to all visual processing. Anyone who claims to be an expert in vision/perception must have a thorough understanding of receptive fields, their various types, how they operate, how they change with conditions and how they determine visual capability. I won’t go into a full explanation of receptive fields because it is too large a topic. However, I will mention two of their properties, inhibition and convergence.

    Individual cones and rods have very similar sensitivity to light. Both respond to a single quantum of light, although rods produce a bigger response. A major difference between day and night vision is inhibition and convergence, the way the photoreceptors are wired together, and the amount of light-sensitive photopigment available. Moreover, most „night vision“ occurs in a mixed rod/cone mode. The overall operation of the eye in diminishing light levels is better described in terms of three operating modes, photopic, mesopic and scotopic. Photopic vision occurs at high light levels and is characterized by 1) cone photoreceptors, 2) low light sensitivity, 3) high acuity and 4) color vision. Scotopic vision occurs at very low light levels and exhibits 1) use of rod photoreceptors, 2) high light sensitivity, 3) poor acuity and 4) no color vision.
    The entire article can be found at this link.

    Bright Lights, Big Problems – Sky & telescope article

    2006 article

    J. Kelly Beatty and Rachel Thessin

    Like death and taxes, there’s no denying that outdoor lighting has become an inescapable part of life. Streetlights adorn our roads, billboards stud our freeways, shopping-center parking lots are aglow from dusk to dawn, businesses obsess over late-night security, and convenience stores outdazzle one another to compete for customers. We cheat the night of darkness and, in the process, create light pollution that robs the sky of stars.

    Electric streetlights have been with us since the 1880s, and it wasn’t long thereafter that some manufacturers recognized the visual and cost-saving benefits of directing light down, onto the ground. In 1918 the Holophane Glass Co. published the very first roadway-lighting manual. Titled The New Era in Street Lighting, it set forth a number of recommended practices, among them the common-sense notion that “Light above the horizontal must be conserved.” In a later section, the manual notes:

    In addition to the two fundamental items of highly efficient lamps and the effective use of the light, as discussed, it is very important to see to it that the street lighting system produces an effect which surrounds the eyes of those using the streets with conditions under which the eye is free to perform its functions properly. Any system which fails in this respect is extravagant — no matter how efficient the lamps nor how efficiently the light may be directed upon the street surfaces or objects. Glare serves seriously to reduce the discerning power of the eye.

    Unfortunately, almost no one heeded this unsung champion of good lighting practices. Instead, artificial skyglow became markedly more obvious in the late 20th century with the widespread use of high-intensity fixtures utilizing mercury-vapor and high-pressure-sodium lamps, and with a societal shift that found more people on the streets at night — and at later hours — than ever before. As our nocturnal wanderings increased, so too did the need for ubiquitous nighttime illumination. Then decision-makers began to equate “more light” with “better safety and security,” even though objective proof of such a relationship did not exist.
    The entire article can be found at this link.

    American Medical Association Addresses Light Pollution

    2012 article

    Camille M. Carlisle

    Researchers are raising several possible health concerns related to nighttime light exposure, among them a higher risk of cancer.

    I usually think of light pollution as astronomers’ concern. Who else would mind if the sky glow is so bright that it washes out Orion? (When I can’t see Orion, I feel jilted — yes, even in the months when it’s below the horizon at night.) But the issue has a broader reach than my petulance. Fighting light pollution isn’t merely about seeing stars; it’s about being sensible in our usage and reducing waste.
    The document’s first human concern is glare, which report coauthor Dr. Mario Motta (Tufts Medical School) outlined for S&T readers back in 2009. Glare’s a pretty standard discussion topic in light-pollution conversations, in part because, as drivers age, their eyes become less able to cope with poorly directed light that scatters inside the eye itself. In 2009 the AMA passed a resolution submitted by Motta supporting the use of fully shielded lights, such as the flat-bottomed street lights. The new report reaffirms that resolution.Still, I was surprised to see that the American Medical Association recently released a report entitled “Light Pollution: Adverse Health Effects of Nighttime Lighting.” It’s a review of some of the available research literature on nighttime lighting’s effect on people; it doesn’t present new research done by the AMA, although many of the results considered come from the authors‘ own work. The report covers a lot of ground, but it’s unclear what the review’s effect will ultimately be.

    Vision researcher Gary Rubin (University College London) agrees with the report’s concern, saying the conclusions are “balanced, well-reasoned and thoroughly researched.” Disability glare — as opposed to “discomfort glare,” which differs from person to person — is definitely a problem for drivers, he says, noting that some cataract patients have had second surgeries to replace their new intraocular lenses with another kind that causes less nighttime glare. And as many of us know from experience, modern halogen and LED headlamps can make nighttime driving downright painful. (I can’t tell you how many times I’ve looked away from an oncoming car’s bright bluish headlights and thought, with scathing condescension, “Is that really necessary?”) Blue-rich light’s destructive effect on the molecule rhodopsin (a.k.a. “visual purple”) in the retina is what makes these headlights hurt so much.
    The entire article can be found at this link.

    The Color-Sensitive Cones

    The Color-Sensitive Cones

    In 1965 came experimental confirmation of a long expected result – there are three types of color-sensitive cones in the retina of the human eye, corresponding roughly to red, green, and blue sensitive detectors.


    More information here.


    2011 article

    Source michaeldmann.net

    Photoreception is a particularly important sense for most primates, including man, but it is not unique to primates or even mammals. Even mollusks have photoreceptors, but one may question whether they possess vision in the same sense as we have it. Most objects reflect light, and because light travels at high speed, it is possible to nearly instantly assess their shape, size, position, speed, and direction of movement. The light rays emanating from an object are gathered and focused onto an array of photoreceptors. Activities generated in the different photoreceptors by the light interact to produce a two-dimensional representation of the object which is transmitted to the brain. The brain then reconstructs a three-dimensional representation using information received from the two eyes. The end-products of the activity of the visual system are sensations that represent the object and its surroundings. These sensations can be used to guide our immediate behavior, or they can be stored for future reference. Visual sensations contain a great deal of information, and understanding these complex phenomena is no simple matter. The best place to begin the study of vision is at the eye itself.

    Fig. 7-1. A section through the human eye illustrating the major structures. (Walls GL: The Vertebrate Eye and its Adaptive Radiations. New York, Hafner, 1967)

    Figure 7-1 shows a cross section through the human eye. It consists of two fluid-filled chambers separated by a transparent structure, the lens. Nearly the entire eye is covered with a tough, fibrous coating called the sclera that is modified anteriorly to form the transparent cornea. The human cornea is about 12 mm in diameter, about 0.5 mm thick in the center and 0.75 to 1 mm thick on the edge, and it is made of the same collagenous connective tissue substance as is the sclera, but the fibers of the cornea are oriented in parallel arrays that let light pass through with minimal scatter, whereas fibers of the sclera are random and light rays are scattered when passing through. The result is that light passes easily through the cornea, but not through the sclera. Lining the inside of the posterior two-thirds of the sclera are two membranes: the choroid, a pigment layer containing the vascular supply for the eyeball as well as mechanisms for maintaining the integrity of the photoreceptors, and the retina that contains the photoreceptors and other neural elements essential to our visual process. The fine structure of the retina will be considered in detail later.

    The human lens is about 11 mm in diameter and 3.5 mm thick at its thickest point, and it is suspended in place by zonule fibers that attach to the ciliary process anterior to the retina. A set of smooth muscle fibers, the ciliary muscle, lie between the ciliary process and sclera. Just anterior to the lens is a pigmented structure called the iris, that is like the diaphragm on some cameras in that it has a hole in the center of variable aperture, the pupil. The pupil is surrounded by two sets of muscles, one that encircles the aperture, the sphincter pupillae, and one that runs radially out from it, the dilator pupillae.

    The anterior chamber of the eye is filled with aqueous humor, a watery fluid of low protein content that is formed from plasma. The vitreous cavity contains a gelatinous substance, the vitreous or vitreous humor. In many people the vitreous is not completely clear, but contains particulate matter that is not transparent. This material may be stationery or may float around, producing „spots before the eyes,“ the floating variety being called „floaters.“
    The entire article can be found here.

    Opponent melanopsin and S-cone signals in the human pupillary light response

    2014 study

    Manuel Spitschan, Sandeep Jain, David H. Brainard, and Geoffrey K. Aguirre. Departments of Psychology and Neurology, University of Pennsylvania, Philadelphia, PA 19104

    In the human, cone photoreceptors (L, M, and S) and the melanopsincontaining, intrinsically photosensitive retinal ganglion cells (ipRGCs) are active at daytime light intensities. Signals from cones are combined both additively and in opposition to create the perception of overall light and color. Similar mechanisms seem to be at work in the control of the pupil’s response to light. Uncharacterized however, is the relative contribution of melanopsin and S cones, with their overlapping, short-wavelength spectral sensitivities. We measured the response of the human pupil to the separate stimulation of the cones and melanopsin at a range of temporal frequencies under photopic conditions. The S-cone and melanopsin photoreceptor channels were found to be low-pass, in contrast to a band-pass response of the pupil to L- and M-cone signals. An examination of the phase relationships of the evoked responses revealed that melanopsin signals add with signals from L and M cones but are opposed by signals from S cones in control of the pupil. The opposition of the S cones is revealed in a seemingly paradoxical dilation of the pupil to greater S-cone photon capture. This surprising result is explained by the neurophysiological properties of ipRGCs found in animal studies.

    Results Using an infrared camera, we measured the consensual PLR of human participants while they observed sinusoidal modulations in the spectrum of a light (Fig. 1B). The stimulus modulations were designed to target specific photoreceptors. The cones and melanopsin have different but overlapping spectral sensitivities. Despite the overlap, it is possible to create sets of light spectra such that the absorption of photons is constant for all of the photoreceptor classes except one (14–16) (Fig. 1C). Modulation between a pair of these “silent substitution” spectra increases and decreases the response of (for example) melanopsin-containing ipRGCs while maintaining nominally constant stimulation of the cones. Separate modulations were designed for melanopsin, S cones, and L+M cones together (a modulation that varied luminance as well as chromaticity). An isochromatic modulation (melanopsin+S+M+L) was also used. All modulations were designed to produce 50% contrast on their targeted photoreceptor(s). Rods were silenced by modulating the spectra about a photopic background (∼800 cd/m2 ). The stimulus was wide-field (27.5°), spatially uniform, and had the central 5° obscured to avoid variation in photoreceptor spectral sensitivity across the visual field caused by the presence of the foveal macular pigment (17). Simulations and control experiments support the specificity of the photoreceptor isolation (Figs. S1–S5 and Table S1). We measured pupil responses from 16 subjects while they observed the different photoreceptor-directed modulations at two for each combination of photoreceptor target and modulation frequency. The two-filter model fits the average amplitude and phase data (Fig. 5A) with parameters similar to those found for subject 01 (Table S2). When expressed as a polar plot (Fig. 5B), the agreement between the group data and model fits is apparent. Interestingly, there is systematic “rotation” of the phase of both the pupil brightness and S-cone responses at the lower temporal frequency that is not captured by the model. This may result from individual differences in the phase of S-cone responses at low temporal frequencies, as is seen between subject 01 and subject 02 (Fig. 4), because the average data do not fully constrain the model and the fits shown are based on parameters obtained for subject 01.

    Whole study on this link

    Night Reader

    night reader

    Do you read before bedtime ? Read on tablet without a blue light, which negatively affects the secretion of melatonin .

    Download Night reader at nightreader.org

    Light spectrum

    480 blue light wavelength
    530 green light wavelength
    580 yelow light wavelength
    610 red light wavelength


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