- Artificial light at night has an adverse impact on human health.
- ALAN is damaging to the environment
- Poorly installed outdoor lighting, especially installations that allow light to be projected upwards, wastes electricity and hence there is an adverse economic impact.
- ALAN brightens the night sky and this makes it more difficult to see the stars.
- Good outdoor lighting installations promote greater safety.
- Here good lighting often implies less light and especially the absence of glare, which is the result of direct illumination from a light source into our eyes. Safer lighting is therefore also lighting which often promotes darker skies.
80% of the world’s population and more than 99% per cent of the US and European populations live under light-polluted skies. The result is that these people may never have seen the Milky Way in all its beauty, and many have never enjoyed the sight of a truly dark and pristine night sky. Those living in the mega-cities of Asia, often with severe air pollution as well as light pollution, may be unable to see stars at night at all.
Light pollution of the night sky occurs when photons from artificial light at night (ALAN) travel up into the atmosphere and are then scattered back down by air molecules or aerosol particles in the Earth’s atmosphere. The result is a brightening of the night sky, increasing its brightness over the naturally occurring value. The bright background of the sky makes stars less visible, given that stars are masked by the sky brightness as a background illumination. The fainter stars disappear first from naked eye vision, and an increasingly greater number become undetectable the brighter the night sky from ALAN.
Light pollution has been defined as the alteration of light levels in the outdoor environment (from those present naturally) that are due to man-made sources of light. Three consequences of light pollution are often cited:
- The brightening of the night sky, known as sky glow;
- The shining of light from a source directly into our eyes, known as glare (which impedes our vision); and
- Light spill (also known as light trespass) in which light shines on areas which were not the targets for illumination.
These are all examples of obtrusive light. They are the consequences of light pollution.
Scattering is an essential process for the sky to brighten. The effect is much exacerbated if light sources are shining upwards, but even for lights only directing photons below the horizontal, reflection off the ground can still contribute to sky brightness. Scattering also renders stars fainter than they would be if observed from the ground instead of from space. At the zenith they are typically about 16 per cent fainter, a phenomenon known as atmospheric extinction.
Our bodies follow a circadian rhythm with a day-night cycle of about 24 hours. This cycle is entrained by the alternating daylight and darkness, to which our bodies are sensitive as a result of the blue-light sensitivity of the photosensitive retinal ganglion cells in our eyes. These cells send a signal to the master control clock of the human body known as the suprachiasmatic nucleus (SCN), embedded in the brain, and this organ in turn controls hormone production in a number of glands.
Of especial importance is melatonin, a hormone produced in the pineal gland only at night as we sleep and only in the absence of blue light. Typically 20 to 60 mg are produced each night for people sleeping in darkness; the half-life in the blood is about 30 minutes, so most of the melatonin has been removed by morning when we rise.
Hormone production in a number of glands is controlled by the day-night cycle to which the retinal ganglion cells are sensitive. Thus the pituitary, pineal (both in the brain), adrenal (on the kidneys) and thyroid (in the throat) glands are all controlled via signals from the SCN, and a variety of different hormones are produced. Several, such as cortisol, serotonin and dopamine, are only produced in the presence of blue light between about 6 am and 10 am, when we rise at dawn after sleep. Many of these hormones are essential contributors to well-being and good mental health. Thus serotonin regulates mood and happiness, as well as appetite and digestion. Dopamine promotes pleasure, alertness and muscle co-ordination. Cortisol allows us to handle stress in our daily lives. These three hormones are neurotransmitters, meaning they relay signals from the body to the brain, and they are all produced in the presence of blue light in the morning. Blue light is therefore essential for human well-being, but it should be synchronized with the natural day-night cycle and be absent at night from about 10 pm to dawn.
Several hormones are produced, like melatonin, in the absence of blue light at night. They include vasoactive intestinal peptide (VIP), which controls blood pressure, and the human growth hormone (hGH), also known as somatotropin, which stimulates growth, cell division and cell regeneration. It is thus important in human development. These six hormones are among those which are tied to a circadian cycle and controlled by blue light or its absence.
As mentioned, melatonin production at night is essential for a good night’s sleep. Quite small amounts of blue light at night or about an hour before going to bed can inhibit melatonin production in the pineal gland. Even with shut eyes during sleep, blue light can penetrate through the eyelids and reach the ganglion cells and thereby disrupt melatonin production. Brief white light levels of a few lux as produced by a computer or cell phone screen may suffice to have an adverse effect on nocturnal hormone production.
The absence or disruption of melatonin secretion does not just produce a sleepless night. Symptoms similar to those associated with jetlag can be the result, and also repeated blue light exposure at night can result in the onset of mood disorders such as irritability, anxiety and depression. Obesity, diabetes and hypertension may also be the result.
Melatonin also plays a role in combatting some cancers, notably breast and prostate cancer. This is because the human immune system is also circadian. Melatonin in the bloodstream activates N-Killer cells and cytotoxic T cells which can destroy viruses and cancer. A huge amount of research in recent years has focussed on the link between blue light at night and the risk of cancer. Some of the circumstantial evidence for this link comes from the higher rates of these cancers in developed countries with more light pollution, and the increase in the cancer rates during the twentieth century as artificial light at night in large cities greatly increased. It also comes from the significantly higher incidence of breast and prostate cancer in night-shift workers, who often sleep during the day in poorly screened bedrooms and have exposure to blue daylight during times of sleep.
All species of living organisms are adversely affected by light pollution, resulting from the desire of humans in urban or semi-urban environments for 24/7 illumination. In many cases this illumination results in increased predation, reduced reproduction or disorientation while migrating or in transit. Light at night can deter nocturnal species from foraging for food, and it can put leaf stress on many plants which lose track of photoperiodism, the alternating cycles of day and night and of the seasons. Many animal species find their habitats become unliveable because of light pollution.
The range of ways that light at night can interfere with the ecosystem is extremely varied, but the list below gives some of the well-documented cases.
- Insects cluster around lights and hence expose themselves to predation from birds or bats;
- Birds that migrate using the stars for navigation cannot do so if the skyglow from artificial light prevents them from seeing so many stars or conceals the Milky Way;
- In urban environments, birds collide with the windows of lit buildings, especially so for office buildings where interior lights are on after dark;
- Turtles that lay their eggs in the sand on sea shores have hatchlings which need to make their way immediately to the ocean; artificial light near the sea shore can attract them in the opposite direction, and they do not find the water. The hatchlings often die from exhaustion or predation;
- Light at night can hinder the metamorphosis of tadpoles into frogs, and hence it results in reduced reproduction of frogs;
- Trees require red light for photosynthesis in their leaves. During this process, tree leaves intake carbon dioxide through stomata and breathe out oxygen during the day. Normally the stomata close at night, but with artificial light they can stay open, which eventually causes leaf necrosis (the leaves die); and
- Most plants are all sensitive to the changing length of day and hence to the seasons. Artificial light at night can disrupt this sensitivity to the season and mean that a deciduous tree may retain its foliage in the autumn and is unable to hibernate properly for the winter months.
The ecosystem of living organisms on Earth evolved over billions of years under an alternating day-night cycle. In just the last 100 years or so, this day-night cycle has been modified by humans producing artificial light so they can engage in various work or leisure activities 24/7. This change in illumination levels is now having profound adverse reactions for many species, both animals and plants.
On a moonless and cloud free night:
- Can you see the Milky Way?
- Can you see the Magellanic Clouds?
- Can you see Omega Centauri?
If you answered ‘Yes’ to the above questions then you are in a dark sky place. At this point you can confirm the extent of the night sky brightness by using a Sky Quality Meter (SQM).
IDA certifies the following categories:
Dark Sky Sanctuary – Sanctuaries are the most remote (and often darkest) places in the world whose conservation state is most fragile.
Dark Sky Reserve – Reserves consist of a dark “core” zone surrounded by a populated periphery where policy controls are enacted to protect the darkness of the core.
Dark Sky Park – Parks are publicly- or privately-owned spaces protected for natural conservation that implement good outdoor lighting and provide dark sky programs for visitors.
Dark Sky Community – Communities are legally organized cities and towns that adopt quality outdoor lighting ordinances and undertake efforts to educate residents about the importance of dark skies.
Urban Dark Sky Park – UNSPs are sites near or surrounded by large urban environs whose planning and design actively promote an authentic night time experience in the midst of significant artificial light at night, and that otherwise do not qualify for designation within any other International Dark Sky Places category.
The process is as follows:
IDA designates IDSPs following an application process requiring applicants to demonstrate robust community support for dark-sky protection and the development of an appropriate lighting management plan together with evidence confirming its intended implementation by the responsible local government body.
Applications are reviewed quarterly by an IDA standing committee composed of dark-sky experts and previously successful programme applicants. Annual updates after designation ensure that IDSPs continue their commitment to dark-sky preservation.
Upon certification, IDA works with certified places to promote their work through media relations, member communications, and social media. An International Dark Sky Place designation helps enhance the visibility of designated locations and foster increased tourism and local economic activity.
The primary objective of IDA Dark Sky certification is the long-term conservation / preservation of the night sky in every place that has been and will be certified.
If you have commenced preparing an application to IDA, please see the Dark Sky Funding Opportunity page.