[2][3][4][5] Specifically, this class of RGCs being discussed is referred to as "intrinsically photosensitive", which just means they are sensitive to light.
[4] Ultimately, via this retinohypothalamic tract (RHT) the suprachiasmatic nucleus (SCN) of the hypothalamus receives light information from these ipRGCs.
[8] Some important structures directly impacted by the light–sleep relationship are the superior colliculus-pretectal area and the ventrolateral pre-optic nucleus.
[6][5] The progressive yellowing of the crystalline lens with age reduces the amount of short-wavelength light reaching the retina and may contribute to circadian alterations observed in older adulthood.
A delay, caused by light exposure before sleeping, means that the individual will tend to wake up later on the following day(s).
The hormones cortisol and melatonin are affected by the signals light sends through the body's nervous system.
[14] In rats, constant light eventually disrupts the cycle to the point that memory and stress coping may be impaired.
[19] The effect this wavelength of light has on melanopsin leads to physiological responses such as the suppression of melatonin production, increased alertness, and alterations to the circadian rhythm.
[4] Seasonal affective disorder creates a model in which decreased day length during autumn and winter increases depressive symptoms.
[6][4] Light seems to have therapeutic antidepressant effects when an organism is exposed to it at appropriate times during the circadian rhythm, regulating the sleep-wake cycle.
[4] Frontal and parietal lobe areas involved in working memory have been implicated in melanopsin responses to light information.
[20] "In 2007, the International Agency for Research on Cancer classified shift work with circadian disruption or chronodisruption as a probable human carcinogen.
By suppressing the production of melatonin over the course of the night rats showed increased rates of tumors over the course of a four-week period.
[22] Artificial light at night causing circadian disruption additionally impacts sex steroid production.
[21] The proper exposure to light has become an accepted way to alleviate some of the effects of seasonal affective disorder (SAD).
In addition exposure to light in the morning has been shown to assist Alzheimer patients in regulating their waking patterns.
In order to more accurately replicate natural cycles lighting users must be able to set a wake and bed time.
For instance, exercise and other physical activity, when coupled with light exposure, results in a somewhat stronger entrainment response.
[32] The time of day at which people are shown a light source that produces visual discomfort is not perceived evenly.