Abstract
The effect of blue LED on melatonin secretion, feeding behaviour and growth was addressed in Holstein female dairy calves. In Exp.1, six animals (8 weeks old, 97 ± 4.1 kg BW) were exposed to yellow or blue LED for 2 hr before darkness over 7 days under a long-day photoperiod (LDPP). In Exp. 2, six animals (8 weeks old, 88.5 ± 4.8 kg BW) were exposed to blue light from a white LED all daytime or a yellow LED for 2 hr before the darkness of LDPP (blue light cut) over 3 weeks. In Exp. 1, blue light mildly suppressed melatonin secretion during the 2-hr treatment but did not affect the timing of the nightly melatonin rise. However, the rise in nighty melatonin levels was higher with yellow than blue LED. In Exp. 2, white LED completely suppressed melatonin secretion during the 2-hr treatment, but plasma melatonin concentrations were similar during the darkness. Grass hay intake, rumination time, frequency of water intake and body weight gain were higher in animals exposed to the yellow rather than the white LED. Overall results indicate that exposure to blue light from white LEDs under an LDPP suppresses melatonin secretion and might negatively impact the development of female dairy calves.
https://pubmed.ncbi.nlm.nih.gov/32219969/
Melatonin and light
Melatonin is a signalling substance found in all living beings: humans, animals and plants. Melatonin is called the body's natural sleep aid. This is because the substance stimulates sleep and sleep quality. Melatonin is also a powerful antioxidant, which strengthens the immune system and helps to protect the body's cells and tissues. In addition, melatonin counteracts rapid ageing, stress and cholesterol.
Description
Where and how is melatonin produced?
In humans, melatonin is produced in the pineal gland of the brain, based on the signal substance serotonin. Serotonin contributes to the regulation of sleep, mood, appetite and memory.
The body's content of serotonin increases at dusk, and the beginning of secretion of melatonin initiates the sleep rhythm. If you have too little serotonin in your body in the evening, it affects the production of melatonin and thus the quality of sleep.
It is important for the production of melatonin that there is enough serotonin available in the body. This is ensured by consuming vitamin B6 and foods that contain tryptophan, which is the precursor to serotonin. These foods include: cottage cheese, brown rice, avocado, bananas, walnuts, tomatoes, soy proteins and turkey.
In addition, the amount of melatonin is largely determined by the brightness of the surroundings. The darker the environment, the more melatonin is produced.
The brightness (day/night) is picked up by photoreceptors in the retina of the eye, which send a message to the body's internal clock - a small group of nerve cells in the brain. The internal clock registers the brightness over time and can thus control the circadian rhythm, and the production of melatonin in the pineal gland.
The production of melatonin is at its peak in 5-10 year olds and then decreases with age.
When is melatonin produced?
The production of melatonin is promoted in darkness and inhibited in light. This is why this hormone is also called the hormone of darkness.
A natural production of melatonin therefore takes place in the evening and especially at night, when the eyes are naturally subjected to darkness - and thus are not exposed to either daylight or artificial lighting.
The use of artificial lighting in the evening and at night decreases the duration of melatonin production. This brings disorder to many of the body's functions and is considered by researchers to be the cause of the increasing incidence of sleep problems, but also breast cancer and other forms of cancer in industrialised countries.
What light affects the production of melatonin?
In our modern world, we are exposed to light pollution in the evening and at night, which comes from indoor and outdoor lighting, computers, TV, tablets and smartphones. This light pollution is characterised by the emission of blue light and creates an imbalance in our natural circadian rhythm by inhibiting the natural production of melatonin. It is the blue light in the light spectrum (446-477 nanometers) that inhibits the production of melatonin.
How long does the body produce melatonin?
Over a 24-hour period, the body can maintain a maximum production of melatonin for 12 consecutive hours at most. Normally, the daily maximum production of melatonin in adults lasts 9-10 hours in a row.
However, there will always be an insignificant minimal production of melatonin, regardless of light conditions.
Melatonin and sleep
The need for sleep can vary greatly from person to person and depends, among other things, on melatonin production. Children and young people need many hours of sleep per day (10-15 hours), while adults and older people can manage with far fewer hours of sleep per day (5-10 hours).
It is therefore important to ensure that the eyes are not exposed to blue light for the recommended 8-10 hours per day, when the body produces the melatonin needed to ensure good sleep in addition to disease-fighting body functions.
If you do not have the opportunity to sleep for 8-10 hours per day, there are simple and side-effect-free methods, such as the use of sleep glasses, to ensure melatonin production anyway, without changing lifestyle.
Melatonin and sleep glasses
The production om melatonin can be ensured by sleep glasses, which block blue light of up to 530 nanometers in the light spectrum.
You can easily watch TV, work with the computer and read with sleep glasses on. You can maintain virtually all your normal activities after dark - and at the same time ensure a healthy and natural production of melatonin.
It is also possible to use special light sources that filter out the blue light, and to mount screen filters directly on the PC and TV and achieve the same effect.
Research regarding melatonin and light
Exposure to blue LED light before the onset of darkness under a long-day photoperiod alters melatonin secretion, feeding behaviour and growth in female dairy calves
Anim Sci J. 2020 Jan-Dec;91(1):e13353. doi: 10.1111/asj.13353.Mabrouk Elsabagh, Mamiko Mon, Yui Takao, Akiko Shinoda, Takashi Watanabe, Shiro Kushibiki, Taketo Obitsu, Toshihisa SuginoPMID: 32219969 / DOI: 10.1111/asj.13353
The effect of blue LED on melatonin secretion, feeding behaviour and growth was investigated in female Holstein dairy calves. The overall results indicate that exposure to blue light from white...
Exposure to blue LED light before the onset of darkness under a long-day photoperiod alters melatonin secretion, feeding behaviour and growth in female dairy calves
The effect of blue LED on melatonin secretion, feeding behaviour and growth was investigated in female Holstein dairy calves. The overall results indicate that exposure to blue light from white LEDs during a full day of lighting suppresses the secretion of melatonin and may have a negative impact on the development of female dairy calves.
Exposure to blue LED light before the onset of darkness under a long-day photoperiod alters melatonin secretion, feeding behaviour and growth in female dairy calves
Anim Sci J. 2020 Jan-Dec;91(1):e13353. doi: 10.1111/asj.13353.
PMID: 32219969 / DOI: 10.1111/asj.13353
Systematic review of light exposure impact on human circadian rhythm
Chronobiol Int. 2019 Feb;36(2):151-170. doi: 10.1080/07420528.2018.1527773. Epub 2018 Oct 12.Leena Tähkämö, Timo Partonen, Anu-Katriina PesonenPMID: 30311830 / DOI: 10.1080/07420528.2018.1527773
A number of studies suggest that mistimed light exposure disrupts the circadian rhythm in humans, potentially causing additional health effects. Further analysis of these 15 reports showed that two hours...
Systematic review of light exposure impact on human circadian rhythm
A number of studies suggest that mistimed light exposure disrupts the circadian rhythm in humans, potentially causing additional health effects. Further analysis of these 15 reports showed that two hours of exposure to blue light (460 nm) in the evening suppresses melatonin, with the maximum melatonin-suppressive effect being achieved at the shortest wavelengths (424 nm, violet). Melatonin secretion and suppression were reduced with age, but the light-induced circadian phase advance was not impaired with age. Exposure to light in the evening, at night and in the morning affected the circadian rhythm and melatonin levels. In addition, even the longest wavelengths (631 nm, red) and intermittent light exposures produced circadian responses, and exposure to low light levels (5-10 lux) at night when sleeping with eyes closed produced a circadian response.
Systematic review of light exposure impact on human circadian rhythm
Chronobiol Int. 2019 Feb;36(2):151-170. doi: 10.1080/07420528.2018.1527773. Epub 2018 Oct 12.
PMID: 30311830 / DOI: 10.1080/07420528.2018.1527773
Abstract
Light is necessary for life, and artificial light improves visual performance and safety, but there is an increasing concern of the potential health and environmental impacts of light. Findings from a number of studies suggest that mistimed light exposure disrupts the circadian rhythm in humans, potentially causing further health impacts. However, a variety of methods has been applied in individual experimental studies of light-induced circadian impacts, including definition of light exposure and outcomes. Thus, a systematic review is needed to synthesize the results. In addition, a review of the scientific evidence on the impacts of light on circadian rhythm is needed for developing an evaluation method of light pollution, i.e., the negative impacts of artificial light, in life cycle assessment (LCA). The current LCA practice does not have a method to evaluate the light pollution, neither in terms of human health nor the ecological impacts. The systematic literature survey was conducted by searching for two concepts: light and circadian rhythm. The circadian rhythm was searched with additional terms of melatonin and rapid-eye-movement (REM) sleep. The literature search resulted to 128 articles which were subjected to a data collection and analysis. Melatonin secretion was studied in 122 articles and REM sleep in 13 articles. The reports on melatonin secretion were divided into studies with specific light exposure (101 reports), usually in a controlled laboratory environment, and studies of prevailing light conditions typical at home or work environments (21 studies). Studies were generally conducted on adults in their twenties or thirties, but only very few studies experimented on children and elderly adults. Surprisingly many studies were conducted with a small sample size: 39 out of 128 studies were conducted with 10 or less subjects. The quality criteria of studies for more profound synthesis were a minimum sample size of 20 subjects and providing details of the light exposure (spectrum or wavelength; illuminance, irradiance or photon density). This resulted to 13 qualified studies on melatonin and 2 studies on REM sleep. Further analysis of these 15 reports indicated that a two-hour exposure to blue light (460 nm) in the evening suppresses melatonin, the maximum melatonin-suppressing effect being achieved at the shortest wavelengths (424 nm, violet). The melatonin concentration recovered rather rapidly, within 15 min from cessation of the exposure, suggesting a short-term or simultaneous impact of light exposure on the melatonin secretion. Melatonin secretion and suppression were reduced with age, but the light-induced circadian phase advance was not impaired with age. Light exposure in the evening, at night and in the morning affected the circadian phase of melatonin levels. In addition, even the longest wavelengths (631 nm, red) and intermittent light exposures induced circadian resetting responses, and exposure to low light levels (5-10 lux) at night when sleeping with eyes closed induced a circadian response. The review enables further development of an evaluation method of light pollution in LCA regarding the light-induced impacts on human circadian system.
https://pubmed.ncbi.nlm.nih.gov/30311830/
Light is necessary for life, and artificial light improves visual performance and safety, but there is an increasing concern of the potential health and environmental impacts of light. Findings from a number of studies suggest that mistimed light exposure disrupts the circadian rhythm in humans, potentially causing further health impacts. However, a variety of methods has been applied in individual experimental studies of light-induced circadian impacts, including definition of light exposure and outcomes. Thus, a systematic review is needed to synthesize the results. In addition, a review of the scientific evidence on the impacts of light on circadian rhythm is needed for developing an evaluation method of light pollution, i.e., the negative impacts of artificial light, in life cycle assessment (LCA). The current LCA practice does not have a method to evaluate the light pollution, neither in terms of human health nor the ecological impacts. The systematic literature survey was conducted by searching for two concepts: light and circadian rhythm. The circadian rhythm was searched with additional terms of melatonin and rapid-eye-movement (REM) sleep. The literature search resulted to 128 articles which were subjected to a data collection and analysis. Melatonin secretion was studied in 122 articles and REM sleep in 13 articles. The reports on melatonin secretion were divided into studies with specific light exposure (101 reports), usually in a controlled laboratory environment, and studies of prevailing light conditions typical at home or work environments (21 studies). Studies were generally conducted on adults in their twenties or thirties, but only very few studies experimented on children and elderly adults. Surprisingly many studies were conducted with a small sample size: 39 out of 128 studies were conducted with 10 or less subjects. The quality criteria of studies for more profound synthesis were a minimum sample size of 20 subjects and providing details of the light exposure (spectrum or wavelength; illuminance, irradiance or photon density). This resulted to 13 qualified studies on melatonin and 2 studies on REM sleep. Further analysis of these 15 reports indicated that a two-hour exposure to blue light (460 nm) in the evening suppresses melatonin, the maximum melatonin-suppressing effect being achieved at the shortest wavelengths (424 nm, violet). The melatonin concentration recovered rather rapidly, within 15 min from cessation of the exposure, suggesting a short-term or simultaneous impact of light exposure on the melatonin secretion. Melatonin secretion and suppression were reduced with age, but the light-induced circadian phase advance was not impaired with age. Light exposure in the evening, at night and in the morning affected the circadian phase of melatonin levels. In addition, even the longest wavelengths (631 nm, red) and intermittent light exposures induced circadian resetting responses, and exposure to low light levels (5-10 lux) at night when sleeping with eyes closed induced a circadian response. The review enables further development of an evaluation method of light pollution in LCA regarding the light-induced impacts on human circadian system.
https://pubmed.ncbi.nlm.nih.gov/30311830/
Melatonin Suppression by Light in Humans Is More Sensitive Than Previously Reported
J Biol Rhythms. 2015 Aug;30(4):351-4. doi: 10.1177/0748730415585413. Epub 2015 May 27.Garen V Vartanian, Benjamin Y Li, Andrew P Chervenak, Olivia J Walch, Weston Pack, Petri Ala-Laurila, Kwoon Y WongPMID: 26017927 / PMCID: PMC4499476 / DOI: 10.1177/0748730415585413
Previous research showed that in humans, light attenuation by melatonin is most sensitive to 460 nm (blue light). Using a protocol that improves data precision, we have found the threshold...
Melatonin Suppression by Light in Humans Is More Sensitive Than Previously Reported
Previous research showed that in humans, light attenuation by melatonin is most sensitive to 460 nm (blue light). Using a protocol that improves data precision, we have found the threshold for human attenuation by melatonin to be ∼10 log photons cm(-2) s(-1) at 460 nm. This finding has far-reaching implications, as there is increasing evidence that nocturnal activation of the circadian system may be detrimental.
Melatonin Suppression by Light in Humans Is More Sensitive Than Previously Reported
J Biol Rhythms. 2015 Aug;30(4):351-4. doi: 10.1177/0748730415585413. Epub 2015 May 27.
PMID: 26017927 / PMCID: PMC4499476 / DOI: 10.1177/0748730415585413
Abstract
The retina drives various non-image-forming photoresponses, including circadian photoentrainment and pupil constriction. Previous investigators showed that in humans, photic suppression of the clock-controlled hormone melatonin is most sensitive to 460-nm blue light, with a threshold of ~12 log photons cm(-2) s(-1). This threshold is surprising because non-image-forming vision is mediated by intrinsically photosensitive retinal ganglion cells, which receive rod-driven synaptic input and can respond to light levels as low as ~7 log photons cm(-2) s(-1). Using a protocol that enhances data precision, we have found the threshold for human melatonin suppression to be ~10 log photons cm(-2) s(-1) at 460 nm. This finding has far-reaching implications since there is mounting evidence that nocturnal activation of the circadian system can be harmful.
https://pubmed.ncbi.nlm.nih.gov/26017927/
The retina drives various non-image-forming photoresponses, including circadian photoentrainment and pupil constriction. Previous investigators showed that in humans, photic suppression of the clock-controlled hormone melatonin is most sensitive to 460-nm blue light, with a threshold of ~12 log photons cm(-2) s(-1). This threshold is surprising because non-image-forming vision is mediated by intrinsically photosensitive retinal ganglion cells, which receive rod-driven synaptic input and can respond to light levels as low as ~7 log photons cm(-2) s(-1). Using a protocol that enhances data precision, we have found the threshold for human melatonin suppression to be ~10 log photons cm(-2) s(-1) at 460 nm. This finding has far-reaching implications since there is mounting evidence that nocturnal activation of the circadian system can be harmful.
https://pubmed.ncbi.nlm.nih.gov/26017927/
Protecting the melatonin rhythm through circadian healthy light exposure
Int J Mol Sci. 2014 Dec 17;15(12):23448-500. doi: 10.3390/ijms151223448.Maria Angeles Bonmati-Carrion, Raquel Arguelles-Prieto, Maria Jose Martinez-Madrid, Russel Reiter, Ruediger Hardeland, Maria Angeles Rol, Juan Antonio MadridPMID: 25526564 / PMCID: PMC4284776 / DOI: 10.3390/ijms151223448
Despite the positive effect of artificial light, we pay a price for the easy access to light at night, namely: disorganisation of our circadian rhythm system or chronodisruption (CD), including...
Protecting the melatonin rhythm through circadian healthy light exposure
Despite the positive effect of artificial light, we pay a price for the easy access to light at night, namely: disorganisation of our circadian rhythm system or chronodisruption (CD), including disturbances in the melatonin rhythm. Epidemiological studies show that chronodisruption is associated with an increased incidence of diabetes, obesity, heart disease, cognitive and affective impairment, premature ageing and some types of cancer. Blue light, which is particularly beneficial during the daytime, appears to be more disruptive at night and produces the strongest melatonin inhibition. Night-time exposure to blue light is currently increasing due to the proliferation of energy-efficient lighting (LEDs) and electronic devices. Thus, the development of lighting systems that preserve the melatonin rhythm may reduce the health risks induced by chronodisruption.
Protecting the melatonin rhythm through circadian healthy light exposure
Int J Mol Sci. 2014 Dec 17;15(12):23448-500. doi: 10.3390/ijms151223448.
PMID: 25526564 / PMCID: PMC4284776 / DOI: 10.3390/ijms151223448
Abstract
Currently, in developed countries, nights are excessively illuminated (light at night), whereas daytime is mainly spent indoors, and thus people are exposed to much lower light intensities than under natural conditions. In spite of the positive impact of artificial light, we pay a price for the easy access to light during the night: disorganization of our circadian system or chronodisruption (CD), including perturbations in melatonin rhythm. Epidemiological studies show that CD is associated with an increased incidence of diabetes, obesity, heart disease, cognitive and affective impairment, premature aging and some types of cancer. Knowledge of retinal photoreceptors and the discovery of melanopsin in some ganglion cells demonstrate that light intensity, timing and spectrum must be considered to keep the biological clock properly entrained. Importantly, not all wavelengths of light are equally chronodisrupting. Blue light, which is particularly beneficial during the daytime, seems to be more disruptive at night, and induces the strongest melatonin inhibition. Nocturnal blue light exposure is currently increasing, due to the proliferation of energy-efficient lighting (LEDs) and electronic devices. Thus, the development of lighting systems that preserve the melatonin rhythm could reduce the health risks induced by chronodisruption. This review addresses the state of the art regarding the crosstalk between light and the circadian system.
https://pubmed.ncbi.nlm.nih.gov/25526564/
Currently, in developed countries, nights are excessively illuminated (light at night), whereas daytime is mainly spent indoors, and thus people are exposed to much lower light intensities than under natural conditions. In spite of the positive impact of artificial light, we pay a price for the easy access to light during the night: disorganization of our circadian system or chronodisruption (CD), including perturbations in melatonin rhythm. Epidemiological studies show that CD is associated with an increased incidence of diabetes, obesity, heart disease, cognitive and affective impairment, premature aging and some types of cancer. Knowledge of retinal photoreceptors and the discovery of melanopsin in some ganglion cells demonstrate that light intensity, timing and spectrum must be considered to keep the biological clock properly entrained. Importantly, not all wavelengths of light are equally chronodisrupting. Blue light, which is particularly beneficial during the daytime, seems to be more disruptive at night, and induces the strongest melatonin inhibition. Nocturnal blue light exposure is currently increasing, due to the proliferation of energy-efficient lighting (LEDs) and electronic devices. Thus, the development of lighting systems that preserve the melatonin rhythm could reduce the health risks induced by chronodisruption. This review addresses the state of the art regarding the crosstalk between light and the circadian system.
https://pubmed.ncbi.nlm.nih.gov/25526564/
Blue light from light-emitting diodes elicits a dose-dependent suppression of melatonin in humans
J Appl Physiol (1985). 2011 Mar;110(3):619-26. doi: 10.1152/japplphysiol.01413.2009. Epub 2010 Dec 16.Kathleen E West, Michael R Jablonski, Benjamin Warfield, Kate S Cecil, Mary James, Melissa A Ayers, James Maida, Charles Bowen, David H Sliney, Mark D Rollag, John P Hanifin, George C BrainardPMID: 21164152 / DOI: 10.1152/japplphysiol.01413.2009
Light dampens the production of melatonin in humans, with the strongest response occurring in the short-wavelength part of the spectrum between 446 and 477 nm (blue light). Blue monochromatic light...
Blue light from light-emitting diodes elicits a dose-dependent suppression of melatonin in humans
Light dampens the production of melatonin in humans, with the strongest response occurring in the short-wavelength part of the spectrum between 446 and 477 nm (blue light). Blue monochromatic light has also been shown to be more effective than longer wavelength light in increasing alertness. A comparison of a mean attenuation of melatonin with 40 μW/cm(2) from 4,000 K white broadband fluorescent light, currently used in most mainstream lighting fixtures, suggests that narrow bandwidth blue LED light may be stronger than 4,000 K white fluorescent light in dampening the production of melatonin.
Blue light from light-emitting diodes elicits a dose-dependent suppression of melatonin in humans
J Appl Physiol (1985). 2011 Mar;110(3):619-26. doi: 10.1152/japplphysiol.01413.2009. Epub 2010 Dec 16.
PMID: 21164152 / DOI: 10.1152/japplphysiol.01413.2009
Abstract
Light suppresses melatonin in humans, with the strongest response occurring in the short-wavelength portion of the spectrum between 446 and 477 nm that appears blue. Blue monochromatic light has also been shown to be more effective than longer-wavelength light for enhancing alertness. Disturbed circadian rhythms and sleep loss have been described as risk factors for astronauts and NASA ground control workers, as well as civilians. Such disturbances can result in impaired alertness and diminished performance. Prior to exposing subjects to short-wavelength light from light-emitting diodes (LEDs) (peak λ = 469 nm; 1/2 peak bandwidth = 26 nm), the ocular safety exposure to the blue LED light was confirmed by an independent hazard analysis using the American Conference of Governmental Industrial Hygienists exposure limits. Subsequently, a fluence-response curve was developed for plasma melatonin suppression in healthy subjects (n = 8; mean age of 23.9 ± 0.5 years) exposed to a range of irradiances of blue LED light. Subjects with freely reactive pupils were exposed to light between 2:00 and 3:30 AM. Blood samples were collected before and after light exposures and quantified for melatonin. The results demonstrate that increasing irradiances of narrowband blue-appearing light can elicit increasing plasma melatonin suppression in healthy subjects (P < 0.0001). The data were fit to a sigmoidal fluence-response curve (R(2) = 0.99; ED(50) = 14.19 μW/cm(2)). A comparison of mean melatonin suppression with 40 μW/cm(2) from 4,000 K broadband white fluorescent light, currently used in most general lighting fixtures, suggests that narrow bandwidth blue LED light may be stronger than 4,000 K white fluorescent light for suppressing melatonin.
https://pubmed.ncbi.nlm.nih.gov/21164152/
Light suppresses melatonin in humans, with the strongest response occurring in the short-wavelength portion of the spectrum between 446 and 477 nm that appears blue. Blue monochromatic light has also been shown to be more effective than longer-wavelength light for enhancing alertness. Disturbed circadian rhythms and sleep loss have been described as risk factors for astronauts and NASA ground control workers, as well as civilians. Such disturbances can result in impaired alertness and diminished performance. Prior to exposing subjects to short-wavelength light from light-emitting diodes (LEDs) (peak λ = 469 nm; 1/2 peak bandwidth = 26 nm), the ocular safety exposure to the blue LED light was confirmed by an independent hazard analysis using the American Conference of Governmental Industrial Hygienists exposure limits. Subsequently, a fluence-response curve was developed for plasma melatonin suppression in healthy subjects (n = 8; mean age of 23.9 ± 0.5 years) exposed to a range of irradiances of blue LED light. Subjects with freely reactive pupils were exposed to light between 2:00 and 3:30 AM. Blood samples were collected before and after light exposures and quantified for melatonin. The results demonstrate that increasing irradiances of narrowband blue-appearing light can elicit increasing plasma melatonin suppression in healthy subjects (P < 0.0001). The data were fit to a sigmoidal fluence-response curve (R(2) = 0.99; ED(50) = 14.19 μW/cm(2)). A comparison of mean melatonin suppression with 40 μW/cm(2) from 4,000 K broadband white fluorescent light, currently used in most general lighting fixtures, suggests that narrow bandwidth blue LED light may be stronger than 4,000 K white fluorescent light for suppressing melatonin.
https://pubmed.ncbi.nlm.nih.gov/21164152/
Wavelength-dependent effects of evening light exposure on sleep architecture and sleep EEG power density in men
Am J Physiol Regul Integr Comp Physiol. 2006 May;290(5):R1421-8. doi: 10.1152/ajpregu.00478.2005. Epub 2006 Jan 26.Mirjam Münch, Szymon Kobialka, Roland Steiner, Peter Oelhafen, Anna Wirz-Justice, Christian CajochenPMID: 16439671 / DOI: 10.1152/ajpregu.00478.2005
Light strongly affects the circadian rhythm in humans via retinal ganglion cells. Their spectral sensitivity is highest in the short-wavelength range of the visible light spectrum, as shown by melatonin...
Wavelength-dependent effects of evening light exposure on sleep architecture and sleep EEG power density in men
Light strongly affects the circadian rhythm in humans via retinal ganglion cells. Their spectral sensitivity is highest in the short-wavelength range of the visible light spectrum, as shown by melatonin suppression, circadian rhythm shifts, acute physiological responses, and subjective alertness. We tested the effect of short-wavelength light (460 nm) on sleep EEG power spectra and sleep structure. Furthermore, blue light significantly shortened rapid eye movement (REM) sleep duration during these two sleep cycles. Thus, the light effects on the dynamics of SWA and REM sleep durations were blue-shifted relative to the three-cone visual photopic system, probably mediated by the circadian rhythm, as a non-imaging visual system. Our results can be interpreted in terms of an induction of a phase delay in the circadian rhythm and/or consequences of a stronger alarming effect after blue light that continues into the sleep phase.
Wavelength-dependent effects of evening light exposure on sleep architecture and sleep EEG power density in men
Am J Physiol Regul Integr Comp Physiol. 2006 May;290(5):R1421-8. doi: 10.1152/ajpregu.00478.2005. Epub 2006 Jan 26.
PMID: 16439671 / DOI: 10.1152/ajpregu.00478.2005
Abstract
Light strongly influences the circadian timing system in humans via non-image-forming photoreceptors in the retinal ganglion cells. Their spectral sensitivity is highest in the short-wavelength range of the visible light spectrum as demonstrated by melatonin suppression, circadian phase shifting, acute physiological responses, and subjective alertness. We tested the impact of short wavelength light (460 nm) on sleep EEG power spectra and sleep architecture. We hypothesized that its acute action on sleep is similar in magnitude to reported effects for polychromatic light at higher intensities and stronger than longer wavelength light (550 nm). The sleep EEGs of eight young men were analyzed after 2-h evening exposure to blue (460 nm) and green (550 nm) light of equal photon densities (2.8 x 10(13) photons x cm(-2) x s(-1)) and to dark (0 lux) under constant posture conditions. The time course of EEG slow-wave activity (SWA; 0.75-4.5 Hz) across sleep cycles after blue light at 460 nm was changed such that SWA was slightly reduced in the first and significantly increased during the third sleep cycle in parietal and occipital brain regions. Moreover, blue light significantly shortened rapid eye movement (REM) sleep duration during these two sleep cycles. Thus the light effects on the dynamics of SWA and REM sleep durations were blue shifted relative to the three-cone visual photopic system probably mediated by the circadian, non-image-forming visual system. Our results can be interpreted in terms of an induction of a circadian phase delay and/or repercussions of a stronger alerting effect after blue light, persisting into the sleep episode.
https://pubmed.ncbi.nlm.nih.gov/16439671/
Light strongly influences the circadian timing system in humans via non-image-forming photoreceptors in the retinal ganglion cells. Their spectral sensitivity is highest in the short-wavelength range of the visible light spectrum as demonstrated by melatonin suppression, circadian phase shifting, acute physiological responses, and subjective alertness. We tested the impact of short wavelength light (460 nm) on sleep EEG power spectra and sleep architecture. We hypothesized that its acute action on sleep is similar in magnitude to reported effects for polychromatic light at higher intensities and stronger than longer wavelength light (550 nm). The sleep EEGs of eight young men were analyzed after 2-h evening exposure to blue (460 nm) and green (550 nm) light of equal photon densities (2.8 x 10(13) photons x cm(-2) x s(-1)) and to dark (0 lux) under constant posture conditions. The time course of EEG slow-wave activity (SWA; 0.75-4.5 Hz) across sleep cycles after blue light at 460 nm was changed such that SWA was slightly reduced in the first and significantly increased during the third sleep cycle in parietal and occipital brain regions. Moreover, blue light significantly shortened rapid eye movement (REM) sleep duration during these two sleep cycles. Thus the light effects on the dynamics of SWA and REM sleep durations were blue shifted relative to the three-cone visual photopic system probably mediated by the circadian, non-image-forming visual system. Our results can be interpreted in terms of an induction of a circadian phase delay and/or repercussions of a stronger alerting effect after blue light, persisting into the sleep episode.
https://pubmed.ncbi.nlm.nih.gov/16439671/
Effects of evening light conditions on salivary melatonin of Japanese junior high school students
J Circadian Rhythms. 2004 Aug 11;2(1):4. doi: 10.1186/1740-3391-2-4.Tetsuo HaradaPMID: 15304196 / PMCID: PMC515180 / DOI: 10.1186/1740-3391-2-4
In a previous study, where adult subjects were exposed to a brightness of 400 lux light for more than 30 minutes or a brightness of 300 lux light for more...
Effects of evening light conditions on salivary melatonin of Japanese junior high school students
In a previous study, where adult subjects were exposed to a brightness of 400 lux light for more than 30 minutes or a brightness of 300 lux light for more than two hours, salivary melatonin concentration decreased during the night to a lower level than when the subjects were exposed to dim lighting. CONCLUSION: Bright light of 2000 lux and even moderate light of 200-300 lux from fluorescent bulbs can inhibit nocturnal melatonin concentration in young people. The brightness of a traditional Japanese fireplace, oil lamp or candle (20-30 lux) could be healthier for children and adolescents because a rapid and distinct increase in blood melatonin concentration appears to occur at night under such dim light, making it easier to fall asleep.
Effects of evening light conditions on salivary melatonin of Japanese junior high school students
J Circadian Rhythms. 2004 Aug 11;2(1):4. doi: 10.1186/1740-3391-2-4.
PMID: 15304196 / PMCID: PMC515180 / DOI: 10.1186/1740-3391-2-4
Abstract
BACKGROUND: In a previous study, when adult subjects were exposed to a level of 400 lux light for more than 30 min or a level of 300 lux light for more than 2 hours, salivary melatonin concentration during the night dropped lower than when the subjects were exposed to dim illumination. It was suggested that such light exposure in adolescents or children during the first half of subjective night in normal life might decrease the melatonin level and prevent the falling into sleep. However, there has been no actual study on the effects of light exposure in adolescents. METHODS: Effects of exposure to the bright light (2000 lux) from fluorescent light bulbs during a period of three hours from 19:30 to 22:30 in one evening were examined on evening salivary melatonin concentrations from 19:45 to 23:40. The control group was exposed to dim light (60 lux) during these three hours. Both the dim light control group [DLCG] and the bright light experimental group [BLEG] consisted of two female and three male adolescent participants aged 14-15 y. RESULTS: The salivary melatonin level increased rapidly from 3.00 pg/ml at 21:45 to 9.18 pg/ml at 23:40 in DLCG, whereas it remained at less than 1.3 pg/ml for the three hours in BLEG. Melatonin concentration by BLEG at 22:30 of the experimental day was lower than that at the same time on the day before the experimental day, whereas it was significantly higher in the experimental day than on the day before the experimental day in DLCG. CONCLUSIONS: Bright lights of 2000 lux and even moderate lights of 200-300 lux from fluorescent light bulbs can inhibit nocturnal melatonin concentration in adolescents. Ancient Japanese lighting from a traditional Japanese hearth, oil lamp or candle (20-30 lux) could be healthier for children and adolescents because rapid and clear increase in melatonin concentration in blood seems to occur at night under such dim light, thus facilitating a smooth falling into night sleep.
https://pubmed.ncbi.nlm.nih.gov/15304196/
BACKGROUND: In a previous study, when adult subjects were exposed to a level of 400 lux light for more than 30 min or a level of 300 lux light for more than 2 hours, salivary melatonin concentration during the night dropped lower than when the subjects were exposed to dim illumination. It was suggested that such light exposure in adolescents or children during the first half of subjective night in normal life might decrease the melatonin level and prevent the falling into sleep. However, there has been no actual study on the effects of light exposure in adolescents. METHODS: Effects of exposure to the bright light (2000 lux) from fluorescent light bulbs during a period of three hours from 19:30 to 22:30 in one evening were examined on evening salivary melatonin concentrations from 19:45 to 23:40. The control group was exposed to dim light (60 lux) during these three hours. Both the dim light control group [DLCG] and the bright light experimental group [BLEG] consisted of two female and three male adolescent participants aged 14-15 y. RESULTS: The salivary melatonin level increased rapidly from 3.00 pg/ml at 21:45 to 9.18 pg/ml at 23:40 in DLCG, whereas it remained at less than 1.3 pg/ml for the three hours in BLEG. Melatonin concentration by BLEG at 22:30 of the experimental day was lower than that at the same time on the day before the experimental day, whereas it was significantly higher in the experimental day than on the day before the experimental day in DLCG. CONCLUSIONS: Bright lights of 2000 lux and even moderate lights of 200-300 lux from fluorescent light bulbs can inhibit nocturnal melatonin concentration in adolescents. Ancient Japanese lighting from a traditional Japanese hearth, oil lamp or candle (20-30 lux) could be healthier for children and adolescents because rapid and clear increase in melatonin concentration in blood seems to occur at night under such dim light, thus facilitating a smooth falling into night sleep.
https://pubmed.ncbi.nlm.nih.gov/15304196/
Adaptation of human pineal melatonin suppression by recent photic history
J Clin Endocrinol Metab. 2004 Jul;89(7):3610-4. doi: 10.1210/jc.2003-032100.Kurt A Smith, Martin W Schoen, Charles A CzeislerPMID: 15240654 / DOI: 10.1210/jc.2003-032100 / J Clin Endocrinol Metab. 2005 Mar;90(3):1370
The human internal clock controls the release of the pineal hormone melatonin, which promotes sleep, lowers body temperature and decreases cognitive performance. We found a significant increase in the attenuation...
Adaptation of human pineal melatonin suppression by recent photic history
The human internal clock controls the release of the pineal hormone melatonin, which promotes sleep, lowers body temperature and decreases cognitive performance. We found a significant increase in the attenuation of melatonin under stimulus at approximately 0.5 lux compared to approximately 200 lux, revealing that humans exhibit circadian adaptation to light.
Adaptation of human pineal melatonin suppression by recent photic history
J Clin Endocrinol Metab. 2004 Jul;89(7):3610-4. doi: 10.1210/jc.2003-032100.
PMID: 15240654 / DOI: 10.1210/jc.2003-032100 / J Clin Endocrinol Metab. 2005 Mar;90(3):1370
Abstract
The human circadian pacemaker controls the timing of the release of the pineal hormone melatonin, which promotes sleep, decreases body temperature, and diminishes cognitive performance. Abnormal melatonin secretion has been observed in psychiatric and circadian disorders. Although melatonin secretion is directly suppressed by exposure to light in a nonlinear intensity-dependent fashion, little research has focused on the effect of prior photic history on this response. We examined eight subjects in controlled laboratory conditions using a within-subjects design. Baseline melatonin secretion was monitored under constant routine conditions and compared with two additional constant routines with a fixed light stimulus for 6.5 h of 200 lux (50 microW/cm(2)) after approximately 3 d of photic exposure during the subjective day of either about 200 lux (50 microW/cm(2)) or about 0.5 lux (0.15 microW/cm(2)). We found a significant increase in melatonin suppression during the stimulus after a prior photic history of approximately 0.5 lux compared with approximately 200 lux, revealing that humans exhibit adaptation of circadian photoreception. Such adaptation indicates that translation of a photic stimulus into drive on the human circadian pacemaker involves more complex temporal dynamics than previously recognized. Further elucidation of these properties could prove useful in potentiating light therapies for circadian and affective disorders.
https://pubmed.ncbi.nlm.nih.gov/15240654/
The human circadian pacemaker controls the timing of the release of the pineal hormone melatonin, which promotes sleep, decreases body temperature, and diminishes cognitive performance. Abnormal melatonin secretion has been observed in psychiatric and circadian disorders. Although melatonin secretion is directly suppressed by exposure to light in a nonlinear intensity-dependent fashion, little research has focused on the effect of prior photic history on this response. We examined eight subjects in controlled laboratory conditions using a within-subjects design. Baseline melatonin secretion was monitored under constant routine conditions and compared with two additional constant routines with a fixed light stimulus for 6.5 h of 200 lux (50 microW/cm(2)) after approximately 3 d of photic exposure during the subjective day of either about 200 lux (50 microW/cm(2)) or about 0.5 lux (0.15 microW/cm(2)). We found a significant increase in melatonin suppression during the stimulus after a prior photic history of approximately 0.5 lux compared with approximately 200 lux, revealing that humans exhibit adaptation of circadian photoreception. Such adaptation indicates that translation of a photic stimulus into drive on the human circadian pacemaker involves more complex temporal dynamics than previously recognized. Further elucidation of these properties could prove useful in potentiating light therapies for circadian and affective disorders.
https://pubmed.ncbi.nlm.nih.gov/15240654/
The relationship between the dim light melatonin onset and sleep on a regular schedule in young healthy adults
Behav Sleep Med. 2003;1(2):102-14. doi: 10.1207/S15402010BSM0102_3.Helen J Burgess, Natasha Savic, Tracey Sletten, Gregory Roach, Saul S Gilbert, Drew DawsonPMID: 15600132 / DOI: 10.1207/S15402010BSM0102_3
The endogenous melatonin onset in dim light is a marker of the circadian rhythm that can be used at the right time to control bright light or exogenous melatonin to...
The relationship between the dim light melatonin onset and sleep on a regular schedule in young healthy adults
The endogenous melatonin onset in dim light is a marker of the circadian rhythm that can be used at the right time to control bright light or exogenous melatonin to induce a desired phase shift. Determining a person's circadian rhythm can be expensive and time-consuming. We investigated the relationship between endogenous low-light melatonin onset and sleep times in 16 young healthy individuals who slept at their usual times for one week. The low-light endogenous melatonin onset occurred about 2 h before bedtime and 14 h after awakening. Wake time and sleep midpoint were significantly associated with endogenous melatonin onset in dim light (r = 0.77, r = 0.68, respectively), but bedtime was not (r = 0.36). The possibility of predicting the low-light endogenous melatonin onset of young healthy normal-bred humans from their sleep times is discussed.
The relationship between the dim light melatonin onset and sleep on a regular schedule in young healthy adults
Behav Sleep Med. 2003;1(2):102-14. doi: 10.1207/S15402010BSM0102_3.
PMID: 15600132 / DOI: 10.1207/S15402010BSM0102_3
Abstract
The endogenous melatonin onset in dim light (DLMO) is a marker of circadian phase that can be used to appropriately time the administration of bright light or exogenous melatonin in order to elicit a desired phase shift. Determining an individual's circadian phase can be costly and time-consuming. We examined the relationship between the DLMO and sleep times in 16 young healthy individuals who slept at their habitual times for a week. The DLMO occurred about 2 hours before bedtime and 14 hours after wake. Wake time and midpoint of sleep were significantly associated with the DLMO (r = 0.77, r = 0.68 respectively), but bedtime was not (r = 0.36). The possibility of predicting young healthy normally entrained people's DLMOs from their sleep times is discussed.
https://pubmed.ncbi.nlm.nih.gov/15600132/
The endogenous melatonin onset in dim light (DLMO) is a marker of circadian phase that can be used to appropriately time the administration of bright light or exogenous melatonin in order to elicit a desired phase shift. Determining an individual's circadian phase can be costly and time-consuming. We examined the relationship between the DLMO and sleep times in 16 young healthy individuals who slept at their habitual times for a week. The DLMO occurred about 2 hours before bedtime and 14 hours after wake. Wake time and midpoint of sleep were significantly associated with the DLMO (r = 0.77, r = 0.68 respectively), but bedtime was not (r = 0.36). The possibility of predicting young healthy normally entrained people's DLMOs from their sleep times is discussed.
https://pubmed.ncbi.nlm.nih.gov/15600132/
An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans
J Physiol. 2001 Aug 15;535(Pt 1):261-7. doi: 10.1111/j.1469-7793.2001.t01-1-00261.x.K Thapan, J Arendt, D J SkenePMID: 11507175 / PMCID: PMC2278766 / DOI: 10.1111/j.1469-7793.2001.t01-1-00261.x
The retinal photopigment(s) that transduces these light responses in humans has not yet been described. We would investigate their spectral sensitivity to produce a response from the light spectrum. Fitting...
An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans
The retinal photopigment(s) that transduces these light responses in humans has not yet been described. We would investigate their spectral sensitivity to produce a response from the light spectrum. Fitting of a series of photopigments in the 420-480 nm range showed that rhodopsin templates between lambda(max) 457 and 462 nm fit the data well (r(2) > or =0.73). Of these, the best fit was to the rhodopsin template with lambda(max) 459 nm (r(2) = 0.74). 5. Our data strongly support a primary role for a novel short-wavelength photopigment in light-induced melatonin suppression, and provide the first direct evidence of a non-rod, non-cone photoreceptive system in humans.
An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans
J Physiol. 2001 Aug 15;535(Pt 1):261-7. doi: 10.1111/j.1469-7793.2001.t01-1-00261.x.
PMID: 11507175 / PMCID: PMC2278766 / DOI: 10.1111/j.1469-7793.2001.t01-1-00261.x
Abstract
1. Non-image forming, irradiance-dependent responses mediated by the human eye include synchronisation of the circadian axis and suppression of pineal melatonin production. The retinal photopigment(s) transducing these light responses in humans have not been characterised. 2. Using the ability of light to suppress nocturnal melatonin production, we aimed to investigate its spectral sensitivity and produce an action spectrum. Melatonin suppression was quantified in 22 volunteers in 215 light exposure trials using monochromatic light (30 min pulse administered at circadian time (CT) 16-18) of different wavelengths (lambda(max) 424, 456, 472, 496, 520 and 548 nm) and irradiances (0.7-65.0 microW cm(-2)). 3. At each wavelength, suppression of plasma melatonin increased with increasing irradiance. Irradiance-response curves (IRCs) were fitted and the generated half-maximal responses (IR(50)) were corrected for lens filtering and used to construct an action spectrum. 4. The resulting action spectrum showed unique short-wavelength sensitivity very different from the classical scotopic and photopic visual systems. The lack of fit (r(2) < 0.1) of our action spectrum with the published rod and cone absorption spectra precluded these photoreceptors from having a major role. Cryptochromes 1 and 2 also had a poor fit to the data. Fitting a series of Dartnall nomograms generated for rhodopsin-based photopigments over the lambda(max) range 420-480 nm showed that rhodopsin templates between lambda(max) 457 and 462 nm fitted the data well (r(2) > or =0.73). Of these, the best fit was to the rhodopsin template with lambda(max) 459 nm (r(2) = 0.74). 5. Our data strongly support a primary role for a novel short-wavelength photopigment in light-induced melatonin suppression and provide the first direct evidence of a non-rod, non-cone photoreceptive system in humans.
https://pubmed.ncbi.nlm.nih.gov/11507175/
1. Non-image forming, irradiance-dependent responses mediated by the human eye include synchronisation of the circadian axis and suppression of pineal melatonin production. The retinal photopigment(s) transducing these light responses in humans have not been characterised. 2. Using the ability of light to suppress nocturnal melatonin production, we aimed to investigate its spectral sensitivity and produce an action spectrum. Melatonin suppression was quantified in 22 volunteers in 215 light exposure trials using monochromatic light (30 min pulse administered at circadian time (CT) 16-18) of different wavelengths (lambda(max) 424, 456, 472, 496, 520 and 548 nm) and irradiances (0.7-65.0 microW cm(-2)). 3. At each wavelength, suppression of plasma melatonin increased with increasing irradiance. Irradiance-response curves (IRCs) were fitted and the generated half-maximal responses (IR(50)) were corrected for lens filtering and used to construct an action spectrum. 4. The resulting action spectrum showed unique short-wavelength sensitivity very different from the classical scotopic and photopic visual systems. The lack of fit (r(2) < 0.1) of our action spectrum with the published rod and cone absorption spectra precluded these photoreceptors from having a major role. Cryptochromes 1 and 2 also had a poor fit to the data. Fitting a series of Dartnall nomograms generated for rhodopsin-based photopigments over the lambda(max) range 420-480 nm showed that rhodopsin templates between lambda(max) 457 and 462 nm fitted the data well (r(2) > or =0.73). Of these, the best fit was to the rhodopsin template with lambda(max) 459 nm (r(2) = 0.74). 5. Our data strongly support a primary role for a novel short-wavelength photopigment in light-induced melatonin suppression and provide the first direct evidence of a non-rod, non-cone photoreceptive system in humans.
https://pubmed.ncbi.nlm.nih.gov/11507175/
Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor
J Neurosci. 2001 Aug 15;21(16):6405-12. doi: 10.1523/JNEUROSCI.21-16-06405.2001.G C Brainard, J P Hanifin, J M Greeson, B Byrne, G Glickman, E Gerner, M D RollagPMID: 11487664 / PMCID: PMC6763155 / DOI: 10.1523/JNEUROSCI.21-16-06405.2001
The aim of this study was to establish an action spectrum for light-induced melatonin suppression that could help elucidate the ocular photoreceptor system for regulation of the human pineal gland....
Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor
The aim of this study was to establish an action spectrum for light-induced melatonin suppression that could help elucidate the ocular photoreceptor system for regulation of the human pineal gland. The action spectrum constructed from these data fits an opsin template (R(2) = 0.91), which identifies 446–477 nm as the most potent wavelength region providing circadian input to regulate melatonin secretion. A single photopigment in humans may be primarily responsible for melatonin suppression, and its maximum absorbance appears to be different from rod and cone photopigments of vision. The data also suggest that this new photopigment is retinaldehyde-based. These results suggest that there is a novel opsin photopigment in the human eye that mediates circadian photoreception.
Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor
J Neurosci. 2001 Aug 15;21(16):6405-12. doi: 10.1523/JNEUROSCI.21-16-06405.2001.
PMID: 11487664 / PMCID: PMC6763155 / DOI: 10.1523/JNEUROSCI.21-16-06405.2001
Abstract
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 light-induced 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 (R(2) = 0.81-0.95). The action spectrum constructed from these data fit an opsin template (R(2) = 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.
https://pubmed.ncbi.nlm.nih.gov/11487664/
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 light-induced 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 (R(2) = 0.81-0.95). The action spectrum constructed from these data fit an opsin template (R(2) = 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.
https://pubmed.ncbi.nlm.nih.gov/11487664/