1. Photobiological effects and light pollution Humans & animals
Prepared by ISR – University of Coimbra
August 2017

2. Summary Light Pollution
1.1. Types of Light Pollution (Sky glow, Glare, Light trespass, Clutter)
2. Effects on Humans
3. Effects on Ecosystems
4. Effects on Wildlife
5. Mitigating light pollution

3. 1. Light Pollution
Light pollution is the presence of anthropogenic light in the night environment.
disrupts ecosystems
has adverse health effects.
interferes with astronomical observatories

4. 1. Light Pollution Types of Light Pollution
There are four main categories of Light Pollution:
Sky glow
Glare
Light trespass
Clutter

5. 1. Light Pollution Types of Light Pollution
Useful luminous flux
Glare
Area to illuminate
Adjacent area
DLOR
ULOR
Light Pollution
Sky
Glow
Light trespass
DLOR - Downward light output ratio
ULOR - upward light output ratio

6. 1. Light Pollution Types of Light Pollution
Sky glow This is the bright diffuse glow that hangs over cities and towns at night. Sky glow could be caused by natural factors, but also often caused by inefficient and artificial lights shinning needlessly into the sky, and further scattered by airborne dust particles, gas and water droplets.

7. 1. Light Pollution Types of Light Pollution
Glare Glare is an unpleasant visual effect caused by unfavourable distribution of luminosity or high contrasts, forcing the eye to adjust rapidly. Two types of glare effects are typically distinguished: Disability glare, which is caused by the scattering of light in the eye which reduces contrast sensitivity, and Discomfort glare, which triggers a subjective sensation of discomfort.

8. 1. Light Pollution Types of Light Pollution
Light Trespass Light trespass occurs when unwanted light enters unwanted areas, unintentionally illuminating other homes, businesses, or areas. A common light trespass problem occurs when a strong light enters the window of one's home from the outside.

9. 1. Light Pollution Types of Light Pollution
Light Clutter Light clutter refers to excessive groupings of lights. Groupings of lights may generate confusion and distract from obstacles. This creates a hazardous environment for drivers because it competes with traffic and navigation signals. Clutter is particularly noticeable on roads where the street lights are badly designed, or where brightly lit advertising surrounds the roadways. It also contributes to other forms of light pollution, including light trespass, glare, and sky glow.

10. Light Pollution 2. Effects on Humans
Recent discovery of intrinsically photosensitive retinal ganglion cells (ipRGC) in our bodies show these are very important in setting the internal clock. The newly identified ganglion cells respond most sensitively to visible blue light and set the internal clock that synchronizes our bodies with the external cycle of day and night. Light that is rich in blue content stimulates the ipRGC photoreceptors, make the pupils smaller, encourages dopamine, serotonin, and cortisol production but suppresses melatonin.
The retina of the human eye is not only made up of rods and cones which predominantly serve visual perception but also intrinsic photosensitive retinal ganglian cells (ipRGC). In 2007 it was discovered that these cells contain melanopsin and are therefore sensitive to light. The maximum sensitivity for the melanopic effect of light is at a wavelength of 490 nm (blue). That means that melanopsin is especially well stimulated at this wavelength.
The effect of this stimulation is that a suppression of the production of the hormone melatonin takes place in the pineal gland. The hormone melatonin plays a central role in the circadian rhythm of man. Especially in the evening, when we are tired, our blood has a high concentration of melatonin which drops as we sleep so that the melatonin level is considerably lower in the morning. Daylight, with its high proportion of blue light (especially in the morning), also contributes to the suppression of melatonin.

11. Light Pollution 2. Effects on Humans
-The retina of the human eye is not only made up of rods and cones which predominantly serve visual perception but also intrinsic photosensitive retinal ganglian cells (ipRGC). -In 2007 it was discovered that these cells contain melanopsin and are therefore sensitive to light. The maximum sensitivity for the melanopic effect of light is at a wavelength of 490 nm (blue). That means that melanopsin is especially well stimulated at this wavelength. -The effect of this stimulation is that a suppression of the production of the hormone melatonin takes place in the pineal gland. The hormone melatonin plays a central role in the circadian rhythm of man. Especially in the evening, when we are tired, our blood has a high concentration of melatonin which drops as we sleep so that the melatonin level is considerably lower in the morning. Daylight, with its high proportion of blue light (especially in the morning), also contributes to the suppression of melatonin.

12. Light Pollution 2. Effects on Humans
The ganglion cells send signals to the brain and regulate hormone production. The four most important hormones that control the biological rhythm are:
Melatonin makes you tired, slows the body functions and lowers activity in favour of rest.
Cortisol on the other hand is a stress hormone that is produced from about 3 am. It stimulates the metabolism and programs the body for day mode.
Serotonin works as a stimulant and motivator. While the cortisol level in the blood drops throughout the day and thereby acts counter-cyclic to the melatonin level, serotonin helps elevate energy levels.
Dopamine plays an important role in muscle coordination, alertness and the pleasure system

13. Light Pollution 2. Effects on Humans
Light varies during the day according to the natural lighting cycle:
Low light levels and low CCTs (Correlated Colour Temperature) in the early morning
High light levels and high CCTs at midday (up to 10,000 K)
Low light levels and low CCTs during evening
Extremely low light levels and a medium CCT under moonlight

14. Light Pollution 2. Effects on Humans
These natural variations of sunlight help determine the timing of our internal clock called the circadian rhythm telling our bodies when to sleep and when to be alert.
Because our sleep-wake cycle is so important, its deregulation may also effect:
Immune system
Memory
Behavior

15. Light Pollution 2. Effects on Humans
Because of the rise in use of white LEDs for outdoor lighting, and their relatively greater short-wavelength content - near the maximum sensitivity for the melanopic effect of light at 490 nm (blue) - compared to the high-pressure sodium (HPS) lamps they are typically replacing, concerns have arisen that the potentially increased presence of short wavelengths in the night environment may be detrimental to health. A number of controlled laboratory studies have shown delays in the normal transition to nighttime physiology from evening exposure to tablet computer screens, backlit e-readers, and room light typical of residential settings.

16. Light Pollution 2. Effects on Humans
The spectral content of LEDs can be engineered to provide any light spectrum desired – for example, to provide more ipRGC stimulation, or less of it, according to the situation or time of day.
However, it is important to note that short wavelengths are a fundamental component of the visible spectrum and also have benefits:
Improved object identification (e.g., of vehicles, clothing, people)
improved contrast between an object (e.g., road debris) and its surroundings.
enhanced peripheral vision at the low levels of illuminance
This means that they cannot be simply removed from outdoor lighting, particulary in road areas.

17. Light Pollution 3. Effects on Ecosystems
Ecological systems are strongly influenced by light, and particularly by daily and seasonal cycles of light and dark.
The introduction of artificial light disrupts these natural light cycles that arise from the movements of the Earth, Moon, and Sun, as well as from meteorological factors.
Day / Night
Seasons
Lunar cycles

18. Light Pollution 3. Effects on Ecosystems
Diurnal (solar) cycle The most obvious change in introducing light at night is the end of darkness in general. The day/night cycle is probably the most powerful environmental behavioral signal, as almost all animals can be categorized as nocturnal or diurnal. If a nocturnal animal is only active in extreme dark, it will be unable to live in lit areas. Many animals use the timings of dawn and dusk, as a cue for daily activities (e.g. foraging). The most acute effects are directly felt next to streetlights and lit buildings, but the diffuse light of skyglow can extend out to hundreds of kilometers away from city centers.

19. Light Pollution 3. Effects on Ecosystems
Seasonal cycles The change in the length of the day is the key signal for seasonal behavior as many animals use day length as a signal for seasonal events (e.g. growth, reproduction, migration). The presence of light at night can result in "seasons out of time" changing the behavior and thermoregulation of affected organisms. This effect can be deadly for small mammals in the winter, since when their body acts as if it's summer they don't maintain an adequate winter body temperature to survive winter nights.

20. Light Pollution 3. Effects on Ecosystems
Lunar cycles The behavior of some animals is regulated by the lunar cycle (e.g. reproduction). Near city centers the level of skyglow often exceeds that of the full moon, so the presence of light at night can alter these behaviors.
For example, reduce synchrony of reproductive activities amongst individuals (with consequences for fertilization success, predator satiation, etc.), and interactions with other important environmental phenomene such as resource availability.

21. Light Pollution 4. Effects on Wildlife
Mammals - Mammals such as bats, raccoons, coyotes, deer, and moose can experience difficulty foraging for food at night due to over illumination. They risk exposure to natural predators and increased mortality due to night vision impairment. They also experience a decline in reproduction that leads to a shrinking population. Birds - Birds such as owls and nighthawks use moonlight and starlight to hunt and migrate at night. Artificial lights sources can overwhelm natural light sources, causing birds to be drawn to or fixated on the artificial lights. This results in birds deviating from their intended migration route, flying until they experience exhaustion and collapse, and becoming prey to other animals. Marine birds such as albatrosses are known to collide with lighthouses, wind turbines, and drilling platforms at sea due to their bright lights. In North America alone, 100 million birds die annually in collisions with illuminated buildings and towers.

22. Light Pollution 4. Effects on Wildlife
Reptiles - Reptiles such as sea turtles are greatly affected by light pollution. Female turtles nest on dark, remote beaches, but bright coastal lights prevent them from finding safe nesting areas for their eggs. This leads the female turtles depositing their eggs in an unsafe areas or in the ocean. Sea turtle hatchlings instinctively crawl toward the brightest part on the beach, which for many centuries was the moonlight and starlit ocean; however, excessive lighting on the beach or near the shore confuses the hatchlings and causes them wander away from the ocean. The hatchlings may be eaten by predators, run over by vehicles, drown in swimming pools, or die from dehydration or exhaustion. Artificial lights may also disorient other nocturnal reptiles.

23. Light Pollution 4. Effects on Wildlife
Amphibians - Sky glow affects amphibians such as frogs, toads, and salamanders in marshes and wetlands. The orange haze confuses and disorients them, which causes a decrease in feeding and mating. It also impairs natural instincts that protect amphibians against natural predators and the elements. Insects - Insects such as moths are naturally attracted to light and may use all their energy to stay near a source of light. This interferes with mating and migration as well as makes them vulnerable to natural predators, which reduces their population. This also affects all species that rely on insects for food or pollination.

24. 5. Mitigating light Pollution
Outdoor lighting should be designed not only to provide light where and when it is needed in an energy-efficient manner, but also to minimise or prevent the problems that can arise from stray light.

25. 5. Mitigating light Pollution
Road lighting should be installed in such a way that the benefits are achieved with the least escape of light in directions where it is not useful or is positively harmful both to health and safety.
Upwards Light Output Ratio (ULOR) should be reduced to 0%
When lighting vertical structures, direct light downwards wherever possible or use of shields, baffles and louvres to help reduce light spillage around and over the structure to a minimum.
Dimming can strongly reduce unnecessary illumination (and saves energy).
Use luminaires with better G ratings (EN 13201)
Whenever possible, the use of short wavelength lighting should be minimized.

26. 5. Mitigating light Pollution
Luminaires are designed to have lighting distributions that are appropriate for specific applications. Virtually any luminaire can generate sky glow, light trespass, and glare if installed improperly or in the wrong application. These problems can be avoided by selecting luminaires that have the appropriate light distribution and spectral content for the application and installing them correctly to limit the light spillage, namely uplight.