Category: articles

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.

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: 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: 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

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


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


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.

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.

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.