Light pollution is the presence of any unwanted, inappropriate, or excessive artificial lighting. In a descriptive sense, the term light pollution refers to the effects of any poorly implemented lighting sources, during the day or night. Light pollution can be understood not only as a phenomenon resulting from a specific source or kind of pollution, but also as a contributor to the wider, collective impact of various sources of pollution.
Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with the surrounding environment. While sleep differs from wakefulness in terms of the ability to react to stimuli, it still involves active brain patterns, making it more reactive than a coma or disorders of consciousness.
Jet lag, desynchronosis, or circadian dysrhythmia, is a temporary physiological condition that occurs when a person's circadian rhythm is out of sync with the time zone they are in, and is a typical result from travelling rapidly across multiple time zones. For example, someone travelling from New York to London, i.e. from west to east, feels as if the time were five hours earlier than local time, and someone travelling from London to New York, i.e. from east to west, feels as if the time were five hours later than local time. The phase shift when travelling from east to west is referred to as phase-delay of the circadian cycle, whereas going west to east is phase-advance of the cycle. Most travellers find that it is harder to adjust time zones when travelling east. Jet lag was previously classified as a circadian rhythm sleep disorder.
A circadian rhythm, or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism and responds to the environment. Circadian rhythms are regulated by a circadian clock whose primary function is to rhythmically co-ordinate biological processes so they occur at the correct time to maximize the fitness of an individual. Circadian rhythms have been widely observed in animals, plants, fungi and cyanobacteria and there is evidence that they evolved independently in each of these kingdoms of life.
Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylight. Daylighting is sometimes used as the main source of light during daytime in buildings. This can save energy in place of using artificial lighting, which represents a major component of energy consumption in buildings. Proper lighting can enhance task performance, improve the appearance of an area, or have positive psychological effects on occupants.
Advanced Sleep Phase Disorder (ASPD), also known as the advanced sleep-phase type (ASPT) of circadian rhythm sleep disorder, is a condition that is characterized by a recurrent pattern of early evening sleepiness and very early morning awakening. This sleep phase advancement can interfere with daily social and work schedules, and results in shortened sleep duration and excessive daytime sleepiness. The timing of sleep and melatonin levels are regulated by the body's central circadian clock, which is located in the suprachiasmatic nucleus in the hypothalamus.
Non-24-hour sleep–wake disorder is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in a society". Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light–dark cycle in nature. Although this sleep disorder is more common in blind people, affecting up to 70% of the totally blind, it can also affect sighted people. Non-24 may also be comorbid with bipolar disorder, depression, and traumatic brain injury. The American Academy of Sleep Medicine (AASM) has provided CRSD guidelines since 2007 with the latest update released in 2015.
Full-spectrum light is light that covers the electromagnetic spectrum from infrared to near-ultraviolet, or all wavelengths that are useful to plant or animal life; in particular, sunlight is considered full spectrum, even though the solar spectral distribution reaching Earth changes with time of day, latitude, and atmospheric conditions.
High-energy visible light is short-wave light in the violet/blue band from 400 to 450 nm in the visible spectrum, which has a number of purported negative biological effects, namely on circadian rhythm and retinal health, which can lead to age-related macular degeneration. Increasingly, blue blocking filters are being designed into glasses to avoid blue light's purported negative effects. However, there is no good evidence that filtering blue light with spectacles has any effect on eye health, eye strain, sleep quality or vision quality.
Dark therapy is the practice of keeping people in complete darkness for extended periods of time in an attempt to treat psychological conditions. The human body produces the melatonin hormone, which is responsible for supporting the circadian rhythms. Darkness seems to help keep these circadian rhythms stable.
Light effects on circadian rhythm are the response of circadian rhythms to light.
Designing lighting for the elderly requires special consideration and care from architects and lighting designers. As people age, they experience neurodegeneration in the retina and in the suprachiasmatic nucleus (SCN). Less light reaches the back of the eyes because the pupils decrease in size as one ages, the lens inside one's eye becomes thicker, and the lens scatters more light, causing objects and colors to appear less vivid. These symptoms are particularly common with persons having alzheimer's disease. Older people also have reduced levels of retinal illuminance, such as having smaller pupils and less transparent crystalline lenses. Furthermore, as an individual ages, they begins to lose retinal neurons, which not only compromises the ability to see but also to register a robust daily pattern of light-dark that is needed to maintain biological rhythms. The 24-hour light-dark cycle is the most important external stimulus for regulating the timing of the circadian cycle.
Charles Andrew Czeisler is a Hungarian-American physician and sleep and circadian researcher. He is a leading researcher and author in the fields of the effects of light on human physiology, circadian rhythms and sleep medicine.
Ecological light pollution is the effect of artificial light on individual organisms and on the structure of ecosystems as a whole.
A chronobiotic is an agent that can cause phase adjustment of the circadian rhythm. That is, it is a substance capable of therapeutically entraining or re-entraining long-term desynchronized or short-term dissociated circadian rhythms in mammals, or prophylactically preventing their disruption following an environmental insult such as is caused by rapid travel across several time zones. The most widely recognized chronobiotic is the hormone melatonin, secreted at night in both diurnal and nocturnal species.
Studies, which include laboratory investigations and field evaluations of population groups that are analogous to astronauts, provide compelling evidence that working long shifts for extended periods of time contributes to sleep deprivation and can cause performance decrements, health problems, and other detrimental consequences, including accidents, that can affect both the worker and others.
Francine Laden is an American epidemiologist who is Professor of Environmental Epidemiology at the Harvard T.H. Chan School of Public Health. Her research has investigated the environmental epidemiology of chronic disease. She serves as co-director of the Harvard University and Boston University center for research on environmental and social stressors in housing across the life course. Laden has also served on the United States Environmental Protection Agency advisory board.
Elizabeth Klerman is a professor of neurology at Harvard Medical School. Her research focuses on applying circadian and sleep research principles to human physiology and pathophysiology. She also uses mathematical analysis and modeling to study human circadian, sleep, and objective neurobehavioral performance and subjective (self-reported) mood and alertness rhythms.
Chronodisruption is a concept in the field of circadian biology that refers to the disturbance or alteration of the body's natural biological rhythms, for example the sleep-wake cycle, due to various environmental factors. The human body is synchronized to a 24-hour light-dark cycle, which is essential for maintaining optimal health and well-being. However, modern lifestyles —which involve exposure to artificial light, irregular sleep schedules, and shift work — can disrupt this natural rhythm, leading to a range of adverse physiological outcomes. Chronodisruption has been linked to a variety of health disorders and diseases, including neurodegenerative diseases, diabetes, mood disorders, cardiovascular disease, and cancer. Such disruptors can lead to dysregulation of hormones and neurotransmitters, though researchers continue to investigate the physiological implications of chronodisruption. Indeed, research in chronobiology is rapidly advancing, with an increasing focus on understanding the underlying mechanisms of chronodisruption and developing strategies to prevent or mitigate its adverse effects. This includes the development of pharmacological interventions, as well as lifestyle modifications such as optimizing one's sleeping environment and timing of meals and physical activity.
The blue light spectrum, characterized by wavelengths between 400 and 500 nanometers, has a broad impact on human health, influencing numerous physiological processes in the human body. Although blue light is essential for regulating circadian rhythms, improving alertness, and supporting cognitive function, its widespread presence has raised worries about its possible effects on general well-being.
