Editing Light pollution (section)

==Consequences==
Light pollution has "detrimental impacts on wildlife, human health, and ecosystem functions and services". Only the damage to ecosystems is estimated as 3.36 trillion dollars per year. Ecosystems which are suffering from the highest level of light pollution, deliver 40% less ecological services.<ref>{{cite journal |last1=Yu |first1=Bailang |last2=Chen |first2=Yunhao |last3=J. Anderson |first3=Sharolyn |last4=Kubiszewski |first4=Ida |last5=C. Sutton |first5=Paul |title=The Ecological Economics of Light Pollution: Impacts on Ecosystem Service Value |journal=Remote Sensing |date=15 July 2024 |volume=16 |issue=Remote Sensing and GIS Technologies for Sustainable Ecosystem Management |page=2591 |doi=10.3390/rs16142591 |doi-access=free |bibcode=2024RemS...16.2591A }}</ref>
=== Public health impact ===

{{see also|Light effects on circadian rhythm|Ecological light pollution}}
[[File:Lichtverschmutzung in Kastelruth.JPG|thumb|right|Streetlights at the ski resort [[Kastelruth]] in [[South Tyrol]], Italy]]

Medical research on the effects of excessive light on the human body suggests that a variety of adverse health effects may be caused by light pollution or excessive light exposure, and some lighting design textbooks<ref>Gary Steffy, ''Architectural Lighting Design'', John Wiley and Sons (2001) {{ISBN|0-471-38638-3}}.</ref> use human health as an explicit criterion for proper interior lighting. Health effects of over-illumination or improper spectral composition of light may include: increased headache incidence, worker [[fatigue (physical)|fatigue]], [[stress (medicine)|medically defined stress]], decrease in [[Human sexuality|sexual]] function and increase in anxiety.<ref>{{Cite journal |last=Rajkhowa |first=Rasna |date=2014 |title=Light Pollution and Impact of Light Pollution |url=https://d1wqtxts1xzle7.cloudfront.net/87472490/T0NUMTQyMTA_-libre.pdf?1655167711=&response-content-disposition=inline%3B+filename%3DLight_Pollution_and_Impact_of_Light_Poll.pdf&Expires=1711526208&Signature=JgCjCdabA5biUDvw1GF7dPaMfpgGGlYOxBIoD4K7sRWbGmAfL0CCWkQPbPD2AM1l8-nfahO0oubK04sdsOT7UUklLAvEOa-Ljel6S2Yah3yI~~nt7PqkK91JO09BB7JXpsFj4l0cUfa0~c6rNno5jAQ-sjnnDU9omC9NrrvqT9zDWxPG5-IYUbfHWg9hXsqKTnTqkafL3FGIg29XtxjVg0rxZhq3J-TaQvaJ-1XWqRGQTJS3R4st-UMUdmtfyhvS0QFoXus7GbKENt6hdgR2uDW76Pfbz~OLlTIg0q1AlttjNw-mi7uTZCH5Lad3Tyb2M1QmwPCvNjWkmxaUqVCtKQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA |journal=International Journal of Science and Research |volume=3 |issue=10 |pages=861–867 |access-date=2024-03-27 |archive-date=2024-03-27 |archive-url=https://web.archive.org/web/20240327070224/https://d1wqtxts1xzle7.cloudfront.net/87472490/T0NUMTQyMTA_-libre.pdf?1655167711=&response-content-disposition=inline%3B+filename%3DLight_Pollution_and_Impact_of_Light_Poll.pdf&Expires=1711526208&Signature=JgCjCdabA5biUDvw1GF7dPaMfpgGGlYOxBIoD4K7sRWbGmAfL0CCWkQPbPD2AM1l8-nfahO0oubK04sdsOT7UUklLAvEOa-Ljel6S2Yah3yI~~nt7PqkK91JO09BB7JXpsFj4l0cUfa0~c6rNno5jAQ-sjnnDU9omC9NrrvqT9zDWxPG5-IYUbfHWg9hXsqKTnTqkafL3FGIg29XtxjVg0rxZhq3J-TaQvaJ-1XWqRGQTJS3R4st-UMUdmtfyhvS0QFoXus7GbKENt6hdgR2uDW76Pfbz~OLlTIg0q1AlttjNw-mi7uTZCH5Lad3Tyb2M1QmwPCvNjWkmxaUqVCtKQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA |url-status=dead }}</ref><ref name="Burks">Burks, Susan L. (1994) ''Managing your Migraine'', Humana Press, New Jersey. {{ISBN|0-89603-277-9}}.</ref><ref name="Cambridge">''Cambridge Handbook of Psychology, Health and Medicine'', edited by Andrew Baum, Robert West, John Weinman, Stanton Newman, Chris McManus, Cambridge University Press (1997) {{ISBN|0-521-43686-9}}</ref><ref name="Pijnenburg">Pijnenburg, L.; Camps, M. and Jongmans-Liedekerken, G. (1991) ''Looking closer at assimilation lighting'', Venlo, GGD, Noord-Limburg</ref><ref name="Knez">{{cite journal|last1=Knez|first1=I|title=Effects of colour of light on nonvisual psychological processes|journal=Journal of Environmental Psychology|volume=21|pages=201–208|date=2001|doi=10.1006/jevp.2000.0198|issue=2}}</ref> Likewise, animal models have been studied demonstrating unavoidable light to produce adverse effect on mood and anxiety.<ref name="sadrodents">{{Cite journal |last1=Fonken |first1=L K |last2=Finy |first2=M S |title=Influence of light at night on murine anxiety- and depressive-like responses |journal = Behavioural Brain Research| volume = 205 |issue=2 | pages = 349–354 | date = 28 December 2009| doi =10.1016/j.bbr.2009.07.001|last3 = Walton| first3 = James C.| last4 = Weil| first4 = Zachary M.| last5 = Workman| first5 = Joanna L.| last6 = Ross| first6 = Jessica| last7 = Nelson| first7 = Randy J.| pmid = 19591880|s2cid=4204514 }}</ref> For those who need to be awake at night, light at night also has an acute effect on alertness and mood.<ref>{{cite journal|doi=10.1177/1477153509360887|date=2010 |author=Plitnick B |author2=Figueiro MG |author3=Wood B |author4=Rea MS|journal=Lighting Research and Technology|title=The effects of long-wavelength red and short-wavelength blue lights on alertness and mood at night|volume=42|issue=4|pages=449–458|s2cid=54032781 }}</ref>

Outdoor artificial light at night – exposure to contemporary types such as current types of street lighting – has been linked to risks for obesity,<ref>{{cite journal |last1=Park |first1=Yong-Moon Mark |last2=White |first2=Alexandra J. |last3=Jackson |first3=Chandra L. |last4=Weinberg |first4=Clarice R. |last5=Sandler |first5=Dale P. |title=Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women |journal=JAMA Internal Medicine |date=1 August 2019 |volume=179 |issue=8 |pages=1061–1071 |doi=10.1001/jamainternmed.2019.0571|pmid=31180469 |pmc=6563591 }}</ref> mental disorders,<ref>{{cite journal |last1=Tancredi |first1=Stefano |last2=Urbano |first2=Teresa |last3=Vinceti |first3=Marco |last4=Filippini |first4=Tommaso |title=Artificial light at night and risk of mental disorders: A systematic review |journal=Science of the Total Environment |date=August 2022 |volume=833 |pages=155185 |doi=10.1016/j.scitotenv.2022.155185|pmid=35417728 |bibcode=2022ScTEn.83355185T |s2cid=248093823 }}</ref> [[diabetes]],<ref>{{cite journal |last1=Zheng |first1=Ruizhi |last2=Xin |first2=Zhuojun |last3=Li |first3=Mian |last4=Wang |first4=Tiange |last5=Xu |first5=Min |last6=Lu |first6=Jieli |last7=Dai |first7=Meng |last8=Zhang |first8=Di |last9=Chen |first9=Yuhong |last10=Wang |first10=Shuangyuan |last11=Lin |first11=Hong |last12=Wang |first12=Weiqing |last13=Ning |first13=Guang |last14=Bi |first14=Yufang |last15=Zhao |first15=Zhiyun |last16=Xu |first16=Yu |title=Outdoor light at night in relation to glucose homoeostasis and diabetes in Chinese adults: a national and cross-sectional study of 98,658 participants from 162 study sites |journal=Diabetologia |date=14 November 2022 |volume=66 |issue=2 |pages=336–345 |doi=10.1007/s00125-022-05819-x |pmid=36372821 |s2cid=253509635 |language=en |issn=1432-0428|doi-access=free }}</ref> and potentially other health issues<ref>{{cite journal |title=Artificial Light at Night: State of the Science 2022 |url=https://www.darksky.org/wp-content/uploads/2022/06/IDA-State-of-the-Science-2022-EN.pdf |publisher=International Dark-Sky Association |access-date=17 December 2022 |doi=10.5281/zenodo.6903500 |date=9 June 2022 |last1=Barentine |first1=John C. |archive-date=1 April 2023 |archive-url=https://web.archive.org/web/20230401022338/https://www.darksky.org/wp-content/uploads/2022/06/IDA-State-of-the-Science-2022-EN.pdf |url-status=live }}</ref> by preliminary studies.<ref>{{cite journal |last1=Zielinska-Dabkowska |first1=K. M. |last2=Schernhammer |first2=E. S. |last3=Hanifin |first3=J. P. |last4=Brainard |first4=G. C. |title=Reducing nighttime light exposure in the urban environment to benefit human health and society |journal=[[Science (journal)|Science]] |date=2023 |volume=380 |issue=6650 |pages=1130–1135 |doi=10.1126/science.adg5277|pmid=37319219 |bibcode=2023Sci...380.1130Z |s2cid=259166063 }}</ref>

In 2007, "shift work that involves circadian disruption" was listed as a probable carcinogen by the World Health Organization's International Agency for Research on Cancer. (IARC Press release No. 180).<ref>{{cite web| title = IARC Monographs Programme finds cancer hazards associated with shiftwork, painting and firefighting, International Agency for Research on Cancer| access-date = 2011-07-06| url = http://www.iarc.fr/en/media-centre/pr/2007/pr180.html| archive-url = https://web.archive.org/web/20110721001355/http://www.iarc.fr/en/media-centre/pr/2007/pr180.html| archive-date = 2011-07-21}}</ref><ref>{{cite book| title = IARC Monograph 98| access-date = 2011-07-06| url = http://monographs.iarc.fr/ENG/Monographs/vol98/index.php| archive-date = 2018-06-15| archive-url = https://web.archive.org/web/20180615141748/http://monographs.iarc.fr/ENG/Monographs/vol98/index.php| url-status = live}}</ref> Multiple studies have documented a correlation between night shift work and the increased incidence of breast and prostate cancer.<ref>{{cite journal|last1=Schernhammer|first1=ES|last2=Schulmeister|first2=K|title=Melatonin and cancer risk: does light at night compromise physiologic cancer protection by lowering serum melatonin levels?|journal=British Journal of Cancer|volume=90|issue=5|pages=941–3|date=2004|pmid=14997186|pmc=2409637|doi=10.1038/sj.bjc.6601626}}</ref><ref>{{cite journal|last1=Hansen|first1=J|title=Increased breast cancer risk among women who work predominantly at night|journal=Epidemiology |volume=12|issue=1|pages=74–7|date=2001|pmid=11138824|doi=10.1097/00001648-200101000-00013|s2cid=34390800|doi-access=free}}</ref><ref>{{cite journal|doi=10.1093/jnci/93.20.1557 |pmid=11604479 |last1=Davis |first1=S |date=2001 |pages=1557–62 |issue=20 |last2=Mirick |volume=93 |journal=Journal of the National Cancer Institute |first2=DK |last3=Stevens |first3=RG |title=Night shift work, light at night, and risk of breast cancer |url=http://depts.washington.edu/epidem/Epi591/JNCI%20Editorial.pdf |archive-url=https://web.archive.org/web/20120513142946/http://depts.washington.edu/epidem/Epi591/JNCI%20Editorial.pdf |archive-date=2012-05-13 |doi-access=free }}</ref><ref>{{cite journal|doi=10.1093/jnci/93.20.1563|last1=Schernhammer|first1=ES|last2=Laden|first2=F|last3=Speizer|first3=FE|last4=Willett|first4=WC|last5=Hunter|first5=DJ|last6=Kawachi|first6=I|last7=Colditz|first7=GA|title=Rotating night shifts and risk of breast cancer in women participating in the nurses' health study|journal=Journal of the National Cancer Institute|volume=93|issue=20|pages=1563–8|date=2001|pmid=11604480|doi-access=free}}</ref><ref>{{cite journal|pmid=16596289|last1=Bullough|first1=JD|date=2006|pages=375–83|issue=4|last2=Rea|volume=17|first2=MS|journal=Cancer Causes & Control|last3=Figueiro|first3=MG|title=Of mice and women: light as a circadian stimulus in breast cancer research|url=http://www.lrc.rpi.edu/programs/lightHealth/pdf/ofmiceandwomen.pdf|doi=10.1007/s10552-005-0574-1|s2cid=13069747|access-date=2010-09-29|archive-date=2019-05-16|archive-url=https://web.archive.org/web/20190516062212/https://www.lrc.rpi.edu/programs/lightHealth/pdf/ofmiceandwomen.pdf}}</ref><ref>{{cite journal|pmid=19142761
|last1=Kloog|first1=I|date=2009|pages=108–25|issue=1|last2=Haim|volume=26|first2=A|journal=Chronobiology International|last3=Stevens|first3=RG|last4=Portnov|first4=BA|title=Global co-distribution of light at night (LAN) and cancers of prostate, colon, and lung in men|doi=10.1080/07420520802694020|s2cid=16501239}}</ref> One study which examined the link between exposure to artificial light at night (ALAN) and levels of [[breast cancer]] in South Korea found that regions which had the highest levels of ALAN reported the highest number of cases of breast cancer. Seoul, which had the highest levels of light pollution, had 34.4% more cases of breast cancer than Ganwon-do, which had the lowest levels of light pollution. This suggested a high correlation between ALAN and the prevalence of breast cancer. It was also found that there was no correlation between other types of cancer such as cervical or lung cancer and ALAN levels.<ref>{{Cite journal|last=Yun Jeong|display-authors=etal|date=2015|title=High prevalence of breast cancer in light polluted areas in urban and rural regions of South Korea:An ecologic study on the treatment prevalence of female cancers based on National Health Insurance data.|journal=Chronobiology International|volume=32|issue=5|pages=657–667|doi=10.3109/07420528.2015.1032413|pmid=25955405|s2cid=38132259|url=https://figshare.com/articles/dataset/High_prevalence_of_breast_cancer_in_light_polluted_areas_in_urban_and_rural_regions_of_South_Korea_An_ecologic_study_on_the_treatment_prevalence_of_female_cancers_based_on_National_Health_Insurance_data/1568204|access-date=2021-10-01|archive-date=2022-05-28|archive-url=https://web.archive.org/web/20220528102753/https://figshare.com/articles/dataset/High_prevalence_of_breast_cancer_in_light_polluted_areas_in_urban_and_rural_regions_of_South_Korea_An_ecologic_study_on_the_treatment_prevalence_of_female_cancers_based_on_National_Health_Insurance_data/1568204|url-status=live}}</ref>

A more recent discussion (2009), written by Professor Steven Lockley, Harvard Medical School, can be found in the CfDS handbook "Blinded by the Light?".<ref>{{cite web |url=http://www.britastro.org/dark-skies/handbook.html |title=CfDS Handbook |publisher=Britastro.org |access-date=2010-09-04 |archive-url=https://web.archive.org/web/20100617011039/http://www.britastro.org/dark-skies/handbook.html |archive-date=2010-06-17 }}</ref> Chapter 4, "Human health implications of light pollution" states that "...{{nbsp}}light intrusion, even if dim, is likely to have measurable effects on sleep disruption and melatonin suppression. Even if these effects are relatively small from night to night, continuous chronic circadian, sleep and hormonal disruption may have longer-term health risks". The New York Academy of Sciences hosted a meeting in 2009 on Circadian Disruption and Cancer.<ref>{{cite web |url=http://network.nature.com/hubs/nyc/events/8335 |title=Event—Circadian Disruption and Cancer on Nature Network |publisher=Network.nature.com |access-date=2010-09-04 |archive-url=https://web.archive.org/web/20110512162244/http://network.nature.com/hubs/nyc/events/8335 |archive-date=2011-05-12 }}</ref> In different wavelengths of light, red light has the least inhibitory effect on melatonin.<ref>{{Cite journal |last=Chepesiuk |first=Ron |date=January 2009 |title=Missing the Dark: Health Effects of Light Pollution |journal=Environmental Health Perspectives |language=en |volume=117 |issue=1 |doi=10.1289/ehp.117-a20 |issn=0091-6765 |pmc=2627884 |pmid=19165374}}</ref><ref name="uchc">{{cite web| last = Cheung| first = Maria| title = Graveyard Shift Work Linked to Cancer| work = news| publisher = University of Connecticut Health Center| date = 2009-11-29| url = http://today.uchc.edu/headlines/2007/nov07/graveyard| access-date = 2012-07-06| archive-date = 2020-11-27| archive-url = https://web.archive.org/web/20201127030939/http://today.uchc.edu/headlines/2007/nov07/graveyard/| url-status = live}}</ref>

In June 2009, the [[American Medical Association]] developed a policy in support of control of light pollution. News about the decision emphasized [[glare (vision)|glare]] as a [[public health]] hazard leading to unsafe driving conditions. Especially in the elderly, glare produces loss of contrast, obscuring night vision.<ref name="Motta-2009" />

A new 2021 study published in the Southern Economic Journal indicates that light pollution may increase by 13% in preterm births before 23 weeks of gestation.<ref>{{cite journal |title=Light pollution, sleep deprivation, and infant health at birth |url=https://onlinelibrary.wiley.com/doi/10.1002/soej.12477 |journal=Southern Economic Journal |year=2021 |doi=10.1002/soej.12477 |access-date=4 March 2021 |last1=Argys |first1=Laura M. |last2=Averett |first2=Susan L. |last3=Yang |first3=Muzhe |volume=87 |issue=3 |pages=849–888 |hdl=10419/185163 |s2cid=92984550 |hdl-access=free |archive-date=17 April 2021 |archive-url=https://web.archive.org/web/20210417152759/https://onlinelibrary.wiley.com/doi/10.1002/soej.12477 |url-status=live }}</ref>

=== Ecological impact ===

{{Main|Ecological light pollution}}

While light at night can be beneficial, neutral, or damaging for individual [[species]], its presence invariably disturbs ecosystems. For example, some species of spiders avoid lit areas, while other species are happy to build their [[spider web|webs]] directly on lamp posts. Since lamp posts attract many flying insects, the spiders that tolerate the light gain an advantage over the spiders that avoid it. This is a simple example of the way in which species frequencies and food webs can be disturbed by the introduction of light at night.

Light pollution poses a serious threat in particular to [[Nocturnality|nocturnal]] wildlife, having negative impacts on plant and animal physiology.<ref>{{cite journal |last1=Jägerbrand |first1=Annika K. |last2=Spoelstra |first2=Kamiel |title=Effects of anthropogenic light on species and ecosystems |journal=[[Science (journal)|Science]] |date=2023 |volume=380 |issue=6650 |pages=1125–1130 |doi=10.1126/science.adg3173|pmid=37319223 |bibcode=2023Sci...380.1125J |s2cid=259166091 |url=https://pure.knaw.nl/portal/en/publications/3f82a70f-504f-4b1a-93bf-bde72a20e2ee |hdl=20.500.11755/3f82a70f-504f-4b1a-93bf-bde72a20e2ee |hdl-access=free }}</ref> It can confuse [[animal navigation]], alter competitive interactions, change predator-prey relations,<ref>{{Cite journal |last1=McMahon |first1=Oak |last2=Smyth |first2=Tim |last3=Davies |first3=Thomas W. |date=2022-03-25 |title=Broad spectrum artificial light at night increases the conspicuousness of camouflaged prey |journal=Journal of Applied Ecology |volume=59 |issue=5 |language=en |pages=1365–2664.14146 |doi=10.1111/1365-2664.14146 |s2cid=247754178 |issn=0021-8901|doi-access=free |bibcode=2022JApEc..59.1324M |hdl=10026.1/18654 |hdl-access=free }}</ref> and cause physiological harm.<ref name="Perry-2008">{{Cite book| last1=Perry| first1=G.| last2=Buchanan| first2=B. W.| last3=Fisher| first3=R. N.| last4=Salmon| first4=M.| last5=Wise| first5=S. E.| chapter=Effects of artificial night lighting on amphibians and reptiles in urban environments| date=2008| editor1-first=J. C.| editor2-first=R. E. J.| editor3-first=B.| title=Urban Herpetology| volume=3| pages=239–256| publisher=Society for the Study of Amphibians and Reptiles| publication-date=2008| isbn=978-0-916984-79-3| editor2-last=Mitchell| editor3-last=Brown| editor1-last=Bartholomew}}</ref> The rhythm of life is orchestrated by the natural diurnal patterns of light and dark, so disruption to these patterns impacts the ecological dynamics.<ref>{{cite journal|doi=10.1890/1540-9295(2004)002[0191:ELP]2.0.CO;2|url=http://www.urbanwildlands.org/Resources/LongcoreRich2004.pdf|title=Ecological light pollution|journal=Frontiers in Ecology and the Environment|date=2004|volume=2|issue=4|pages=191–198|last1=Longcore|first1=Travis|last2=Rich|first2=Catherine|doi-access=free|access-date=2005-07-29|archive-date=2011-05-12|archive-url=https://web.archive.org/web/20110512162227/http://www.urbanwildlands.org/Resources/LongcoreRich2004.pdf|url-status=live}}</ref> Many species of marine plankton, such as ''Calanus'' copepods, can detect light levels as low as 0.1 μWm<sup>−2</sup>;<ref>{{Cite journal |last1=Båtnes |first1=Anna S. |last2=Miljeteig |first2=Cecilie |last3=Berge |first3=Jørgen |last4=Greenacre |first4=Michael |last5=Johnsen |first5=Geir |date=January 2015 |title=Quantifying the light sensitivity of Calanus spp. during the polar night: potential for orchestrated migrations conducted by ambient light from the sun, moon, or aurora borealis? |url=http://link.springer.com/10.1007/s00300-013-1415-4 |journal=Polar Biology |language=en |volume=38 |issue=1 |pages=51–65 |doi=10.1007/s00300-013-1415-4 |bibcode=2015PoBio..38...51B |s2cid=11754884 |issn=0722-4060}}</ref> using this as a threshold a global atlas of marine Artificial Light at Night has been generated,<ref>{{Cite journal |last1=Smyth |first1=T. J. |last2=Wright |first2=A. E. |last3=McKee |first3=D. |last4=Tidau |first4=S. |last5=Tamir |first5=R. |last6=Dubinsky |first6=Z. |last7=Iluz |first7=D. |last8=Davies |first8=T. W. |date=2021-12-13 |title=A global atlas of artificial light at night under the sea |journal=Elementa: Science of the Anthropocene |volume=9 |issue=1 |pages=00049 |doi=10.1525/elementa.2021.00049 |bibcode=2021EleSA...9...49S |s2cid=245169968 |issn=2325-1026|doi-access=free |hdl=10037/24006 |hdl-access=free }}</ref> showing its global widespread nature.

Studies suggest that light pollution around lakes prevents zooplankton, such as ''[[Daphnia]]'', from eating surface [[algae]], causing [[algal bloom]]s that can kill off the lakes' plants and lower water quality.<ref>{{cite journal| author=Moore, Marianne V.| author2=Pierce, Stephanie M.| author3=Walsh, Hannah M.| author4=Kvalvik, Siri K.| author5=Julie D. Lim| name-list-style=amp| url=http://www.wellesley.edu/Biology/Faculty/Mmoore/Content/Moore_2000.pdf| title=Urban light pollution alters the diel vertical migration of Daphnia| journal=Verh. Internat. Verein. Limnol| volume=27| date=2000| issue=2| page=779| doi=10.1080/03680770.1998.11901341| bibcode=2000SILP...27..779M| access-date=2005-05-29| archive-date=2005-10-21| archive-url=https://web.archive.org/web/20051021232549/http://www.wellesley.edu/Biology/Faculty/Mmoore/Content/Moore_2000.pdf| url-status=dead}}</ref> Light pollution may also affect ecosystems in other ways. For example, [[entomologist]]s have documented that nighttime light may interfere with the ability of moths and other nocturnal insects to navigate.<ref>{{cite journal|author=Frank, Kenneth D.|url=http://www.darksky.org/infoshts/is109.html|title=Impact of outdoor lighting on moths|journal=Journal of the Lepidopterists' Society|date=1988|volume=42|pages=63–93|archive-url=https://web.archive.org/web/20060617110107/http://www.darksky.org/infoshts/is109.html|archive-date=2006-06-17}}</ref> It can also negative impact on insect development and reproduction.<ref>{{Cite journal|last1=Boyes|first1=Douglas H.|last2=Evans|first2=Darren M.|last3=Fox|first3=Richard|last4=Parsons|first4=Mark S.|last5=Pocock|first5=Michael J. O.|date=2021|title=Is light pollution driving moth population declines? A review of causal mechanisms across the life cycle|journal=Insect Conservation and Diversity|language=en|volume=14|issue=2|pages=167–187|doi=10.1111/icad.12447|s2cid=224956373|issn=1752-4598|doi-access=free}}</ref> Night-blooming flowers that depend on moths for [[pollination]] may be affected by night lighting, as there is no replacement [[pollinator]] that would not be affected by the artificial light. This can lead to species decline of plants that are unable to reproduce, and change an area's longterm [[ecology]].<ref>[https://www.theatlantic.com/science/archive/2017/08/confirmed-night-lights-drive-pollinators-away-from-plants/535983/ Confirmed: Night Lights Drive Pollinators Away From Plants] {{Webarchive|url=https://web.archive.org/web/20180708104417/https://www.theatlantic.com/amp/article/535983/ |date=2018-07-08 }} The Atlantic, 2017</ref> Among nocturnal insects, [[Firefly|fireflies]] ([[Beetle|Coleoptera]]: Lampyridae, Phengodidae and Elateridae) are especially interesting study objects for light pollution, once they depend on their own light to reproduce and, consequently, are very sensitive to environmental levels of light.<ref name="Longcore, Travis-2006" /><ref>{{Cite journal|last1=Lloyd|first1=James E.|last2=Wing|first2=Steven R.|last3=Hongtrakul|first3=Tawatchai|date=1989|title=Ecology, Flashes, and Behavior of Congregating Thai Fireflies|jstor=2388290|journal=Biotropica|volume=21|issue=4|pages=373–376|doi=10.2307/2388290|bibcode=1989Biotr..21..373L }}</ref><ref>{{Cite journal|last1=Firebaugh|first1=Ariel|last2=Haynes|first2=Kyle J.|date=2016-12-01|title=Experimental tests of light-pollution impacts on nocturnal insect courtship and dispersal|journal=Oecologia|language=en|volume=182|issue=4|pages=1203–1211|doi=10.1007/s00442-016-3723-1|issn=0029-8549|bibcode=2016Oecol.182.1203F|pmid=27646716|s2cid=36670391}}</ref> Fireflies are well known and interesting to the general public (unlike many other insects)<ref>{{Cite journal|last1=Picchi|first1=Malayka Samantha|last2=Avolio|first2=Lerina|last3=Azzani|first3=Laura|last4=Brombin|first4=Orietta|last5=Camerini|first5=Giuseppe|date=2013-08-01|title=Fireflies and land use in an urban landscape: the case of Luciola italica L. (Coleoptera: Lampyridae) in the city of Turin|journal=Journal of Insect Conservation|language=en|volume=17|issue=4|pages=797–805|doi=10.1007/s10841-013-9562-z|bibcode=2013JICon..17..797P |s2cid=17204044|issn=1366-638X}}</ref> and are easily spotted by non-experts, and, due to their sensibility and rapid response to environmental changes, good [[bioindicator]]s for artificial night lighting.<ref>{{Cite journal|last1=Viviani|first1=Vadim Ravara|last2=Rocha|first2=Mayra Yamazaki|last3=Hagen|first3=Oskar|date=June 2010|title=Bioluminescent beetles (Coleoptera: Elateroidea: Lampyridae, Phengodidae, Elateridae) in the municipalities of Campinas, Sorocaba-Votorantim and Rio Claro-Limeira (SP, Brazil): biodiversity and influence of urban sprawl|journal=Biota Neotropica|volume=10|issue=2|pages=103–116|doi=10.1590/S1676-06032010000200013|issn=1676-0603|doi-access=free}}</ref> Significant declines in some insect populations have been suggested as being at least partially mediated by artificial lights at night.<ref>{{Cite journal|last1=Grubisic|first1=M.|last2=van Grunsven|first2=R.H.A.|last3=Kyba|first3=C.C.M.|last4=Manfrin|first4=A.|last5=Hölker|first5=F.|date=2018-06-11|title=Insect declines and agroecosystems: does light pollution matter?|journal=Annals of Applied Biology|volume=173|issue=2|pages=180–189|language=en|doi=10.1111/aab.12440|s2cid=89892699|issn=0003-4746|url=http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:3275891|doi-access=free}}</ref><ref>{{Cite journal|last1=Boyes|first1=Douglas H.|last2=Evans|first2=Darren M.|last3=Fox|first3=Richard|last4=Parsons|first4=Mark S.|last5=Pocock|first5=Michael J. O.|date=August 2021|title=Street lighting has detrimental impacts on local insect populations|journal=Science Advances|volume=7|issue=35|pages=eabi8322|language=EN|doi=10.1126/sciadv.abi8322|pmc=8386932|pmid=34433571|bibcode=2021SciA....7.8322B}}</ref><ref>{{Cite journal|date=2020-01-01|title=Light pollution is a driver of insect declines|url=https://www.sciencedirect.com/science/article/abs/pii/S0006320719307797|journal=Biological Conservation|language=en|volume=241|pages=108259|doi=10.1016/j.biocon.2019.108259|issn=0006-3207|last1=Owens|first1=Avalon C.S.|last2=Cochard|first2=Précillia|last3=Durrant|first3=Joanna|last4=Farnworth|first4=Bridgette|last5=Perkin|first5=Elizabeth K.|last6=Seymoure|first6=Brett|bibcode=2020BCons.24108259O|s2cid=209570356|access-date=2021-09-18|archive-date=2021-09-18|archive-url=https://web.archive.org/web/20210918115908/https://www.sciencedirect.com/science/article/abs/pii/S0006320719307797|url-status=live}}</ref>
[[File:Scorpion in arizona.jpg|thumb|A scorpion hides under rocks.]]
[[File:Birds flying trace.jpg|alt=Birds flying trace and star trail near Rio de Janeiro beach at night time in light pollution|thumb|Birds flying trace and star trail near Rio de Janeiro beach at night time in light pollution]]
[[File:Brazil star trails and birds in light pollution photography in Rio beach at night.jpg|alt=Brazil star trails and birds in light pollution in Rio beach at night|thumb|Brazil star trails and birds in light pollution in Rio beach at night]]

A 2009 study<ref name="PolarizedLightEnv">{{cite journal|author2=Gábor Horváth|author3=György Kriska|author4=Péter Malik|author5=Bruce Robertson|title=Polarized light pollution: a new kind of ecological photopollution|journal=Frontiers in Ecology and the Environment|volume=7|issue=6 |date=August 2009|pages=317–325|doi=10.1890/080129|last1=Horváth|first1=Gábor|doi-access=free|bibcode=2009FrEE....7..317H }}</ref> also suggests deleterious impacts on animals and ecosystems because of perturbation of polarized light or artificial polarization of light (even during the day, because direction of natural polarization of sun light and its reflection is a source of information for a lot of animals). This form of pollution is named [[polarized light pollution]] (PLP). Unnatural polarized light sources can trigger maladaptive behaviors in polarization-sensitive taxa and alter ecological interactions.<ref name="PolarizedLightEnv" />

Lights on tall structures can disorient migrating birds. Estimates by the U.S. Fish and Wildlife Service of the number of birds killed after being attracted to tall towers range from four to five million per year to an order of magnitude higher.<ref>{{cite journal|author=Malakoff, D. |title=Faulty towers|journal=Audubon|date=2001|volume=103|pages=78–83 | issue=5}}</ref> The Fatal Light Awareness Program (FLAP) works with building owners in [[Toronto]], [[Ontario]], Canada and other cities to reduce mortality of birds by turning out lights during migration periods. Another study has found that the lights produced by the [[Post Tower]] has affected 25 bird species. As a result, they discovered that decreasing the use of excessive lights increased the survival rate of bird species.<ref>{{Cite journal |last1=Korner |first1=Pius |last2=von Maravic |first2=Irina |last3=Haupt |first3=Heiko |date=2022-07-01 |title=Birds and the 'Post Tower' in Bonn: a case study of light pollution |journal=Journal of Ornithology |language=en |volume=163 |issue=3 |pages=827–841 |doi=10.1007/s10336-022-01985-2 |s2cid=248788275 |issn=2193-7206|doi-access=free |bibcode=2022JOrni.163..827K }}</ref>

Similar disorientation has also been noted for bird species migrating close to offshore production and drilling facilities. Studies carried out by Nederlandse Aardolie Maatschappij b.v. (NAM) and Shell have led to the development and trial of new lighting technologies in the North Sea. In early 2007, the lights were installed on the Shell production platform L15. The experiment proved a great success since the number of birds circling the platform declined by 50 to 90%.<ref>{{cite web |url=http://www.nam.nl/home/Framework?siteId=nam-nl |title=Welkom op de site van de Nederlandse Aardolie Maatschappij BV |publisher=Nam.nl |date=2009-03-26 |access-date=2010-09-04 |archive-date=2011-02-02 |archive-url=https://web.archive.org/web/20110202233013/http://www.nam.nl/home/Framework?siteId=nam-nl }}</ref>

Birds migrate at night for several reasons. They save water from dehydration in hot day flying, and part of the bird's navigation system works with stars in some way. With city light outshining the night sky, birds (and also about mammals) no longer navigate by stars.<ref>{{Cite web|date=2020-10-15|title=در سایه‌ی نور‌ها|url=https://parisabajelan.com/brazil-birds-and-light-pollution/|access-date=2020-10-16|website=پریسا باجلان|language=fa-IR|archive-date=2021-04-10|archive-url=https://web.archive.org/web/20210410195730/https://parisabajelan.com/brazil-birds-and-light-pollution/|url-status=dead}}</ref>

[[Sea turtle]] hatchlings emerging from nests on beaches are another casualty of light pollution. It is a common misconception that hatchling sea turtles are attracted to the moon. Rather, they find the ocean by moving away from the dark silhouette of dunes and their vegetation, a behavior with which artificial lights interfere.<ref>{{cite journal|author=Salmon, M.|url=http://www.seaturtle.org/PDF/Salmon_2003_Biologist.pdf|title=Artificial night lighting and sea turtles|journal=Biologist|date=2003|volume=50|pages=163–168}}{{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> The breeding activity and reproductive phenology of toads, however, are cued by moonlight.<ref>{{cite journal| title=The lunar cycle: a cue for amphibian reproductive phenology?| journal=Animal Behaviour| volume=78|date=2009|pages=349–357| doi=10.1016/j.anbehav.2009.05.007| issue=2| last1=Grant| first1=Rachel A.| last2=Chadwick| first2=Elizabeth A.| last3=Halliday| first3=Tim| s2cid=53169271}}</ref> Juvenile seabirds are also disoriented by lights as they leave their nests and fly out to sea, causing events of high mortality.<ref>{{cite journal|last1=RodrÍguez|first1=Airam|last2=RodrÍguez|first2=Beneharo|title=Attraction of petrels to artificial lights in the Canary Islands: effects of the moon phase and age class|journal=Ibis|volume=151|pages=299–310|date=2009|doi=10.1111/j.1474-919X.2009.00925.x|issue=2|hdl=10261/45133|hdl-access=free}}</ref><ref>{{Cite journal| doi = 10.1111/j.1469-1795.2012.00544.x| title = Factors affecting mortality of shearwaters stranded by light pollution| journal = Animal Conservation| volume = 15| issue = 5| pages = 519–526| year = 2012| last1 = Rodríguez| first1 = A.| last2 = Rodríguez| first2 = B.| last3 = Curbelo| first3 = Á. J.| last4 = Pérez| first4 = A.| last5 = Marrero| first5 = S.| last6 = Negro| first6 = J. J.| bibcode = 2012AnCon..15..519R| url = https://digital.csic.es/bitstream/10261/60076/1/Rodr%c3%adguez%20et%20al%202012%20Anim%20Conserv.pdf| hdl = 10261/60076| s2cid = 36944990| hdl-access = free| access-date = 2018-04-20| archive-date = 2021-04-15| archive-url = https://web.archive.org/web/20210415095650/https://digital.csic.es/bitstream/10261/60076/1/Rodr%c3%adguez%20et%20al%202012%20Anim%20Conserv.pdf| url-status = live}}</ref><ref>{{Cite journal | doi = 10.1371/journal.pone.0110114| title = Fatal Attraction of Short-Tailed Shearwaters to Artificial Lights| journal = PLOS ONE| volume = 9| issue = 10| pages = e110114| year = 2014| last1 = Rodríguez | first1 = A. | last2 = Burgan | first2 = G. | last3 = Dann | first3 = P. | last4 = Jessop | first4 = R. | last5 = Negro | first5 = J. J. | last6 = Chiaradia | first6 = A. | pmid=25334014 | pmc=4198200|bibcode = 2014PLoSO...9k0114R | doi-access = free}}</ref><ref>{{cite journal |last1=Rodríguez |first1=Airam |last2=Holmes |first2=Nick D. |last3=Ryan |first3=Peter G. |last4=Wilson |first4=Kerry-Jayne |last5=Faulquier |first5=Lucie |last6=Murillo |first6=Yovana |last7=Raine |first7=André F. |last8=Penniman |first8=Jay F. |last9=Neves |first9=Verónica |last10=Rodríguez |first10=Beneharo |last11=Negro |first11=Juan J. |last12=Chiaradia |first12=André |last13=Dann |first13=Peter |last14=Anderson |first14=Tracy |last15=Metzger |first15=Benjamin |last16=Shirai |first16=Masaki |last17=Deppe |first17=Lorna |last18=Wheeler |first18=Jennifer |last19=Hodum |first19=Peter |last20=Gouveia |first20=Catia |last21=Carmo |first21=Vanda |last22=Carreira |first22=Gilberto P. |last23=Delgado-Alburqueque |first23=Luis |last24=Guerra-Correa |first24=Carlos |last25=Couzi |first25=François-Xavier |last26=Travers |first26=Marc |last27=Corre |first27=Matthieu Le |title=Seabird mortality induced by land-based artificial lights: Seabird Mortality and Artificial Lights |journal=Conservation Biology |date=October 2017 |volume=31 |issue=5 |pages=986–1001 |doi=10.1111/cobi.12900|pmid=28151557 |hdl=10400.3/4515 |hdl-access=free }}</ref> Amphibians and reptiles are also affected by light pollution. Introduced light sources during normally dark periods can disrupt levels of melatonin production. Melatonin is a hormone that regulates photoperiodic physiology and behaviour. Some species of frogs and salamanders utilize a light-dependent "compass" to orient their migratory behaviour to breeding sites. Introduced light can also cause developmental irregularities, such as retinal damage, reduced juvenile growth, premature metamorphosis,<ref>{{Cite journal|last1=Dananay|first1=Kacey L.|last2=Benard|first2=Michael F.|date=2018-07-11|title=Artificial light at night decreases metamorphic duration and juvenile growth in a widespread amphibian|journal=Proc. R. Soc. B|language=en|volume=285|issue=1882|pages=20180367|doi=10.1098/rspb.2018.0367|pmid=30051829|pmc=6053935|issn=0962-8452}}</ref> reduced sperm production, and genetic mutation.<ref name="Perry-2008" /><ref>{{cite journal|last1=Rowan|first1=William|title=Light and seasonal reproduction in animals|journal=Biological Reviews|volume=13|pages=374–401|date=1938|doi=10.1111/j.1469-185X.1938.tb00523.x|issue=4|s2cid=84548036}}</ref><ref>{{cite journal|author=Scheling, L. |date=2006|title= Ecological Consequences of Artificial Night Lighting|volume=27|issue=3|journal=Natural Areas Journal|pages=281–282|doi=10.3375/0885-8608(2007)27[281:ecoanl]2.0.co;2|s2cid=83768296 }}</ref><ref name="Longcore, Travis-2006">{{cite book|author=Rich, Catherine |author2=Longcore, Travis |name-list-style=amp|title=Ecological consequences of artificial night lighting|publisher=Island Press|date=2006|isbn=978-1-55963-128-0}}</ref><ref>{{cite journal|last1=Woltz|first1=H|last2=Gibbs|first2=J|last3=Ducey|first3=P|title=Road crossing structures for amphibians and reptiles: Informing design through behavioral analysis|journal=Biological Conservation|volume=141|pages=2745–2750|date=2008|doi=10.1016/j.biocon.2008.08.010|issue=11|bibcode=2008BCons.141.2745W|s2cid=82932376|url=http://www.escholarship.org/uc/item/0tm3n517|access-date=2019-01-14|archive-date=2020-02-17|archive-url=https://web.archive.org/web/20200217170314/https://escholarship.org/uc/item/0tm3n517|url-status=live}}</ref><ref>{{cite journal|last1=Barrett|first1=K|last2=Guyer|first2=C|title=Differential responses of amphibians and reptiles in riparian and stream habitats to land use disturbances in western Georgia, USA|journal=Biological Conservation|volume=141|pages=2290–2300|date=2008|doi=10.1016/j.biocon.2008.06.019|issue=9|bibcode=2008BCons.141.2290B}}</ref> Close to global coastal megacities (e.g. Tokyo, Shanghai), the natural illumination cycles provided by the moon in the marine environment are considerably disrupted by light pollution, with only nights around the full moon providing greater radiances, and over a given month lunar dosages may be a factor of 6 less than light pollution dosages.<ref>{{Cite journal |last1=Smyth |first1=T. J. |last2=Wright |first2=A. E. |last3=Edwards-Jones |first3=A. |last4=McKee |first4=D. |last5=Queirós |first5=A. |last6=Rendon |first6=O. |last7=Tidau |first7=S. |last8=Davies |first8=T. W. |date=2022 |title=Disruption of marine habitats by artificial light at night from global coastal megacities |journal=Elementa: Science of the Anthropocene |volume=10 |issue=1 |page=00042 |doi=10.1525/elementa.2022.00042 |bibcode=2022EleSA..10...42S |s2cid=254213236 |issn=2325-1026|doi-access=free |hdl=10037/28198 |hdl-access=free }}</ref>

In September 2009, the 9th European Dark-Sky Symposium in Armagh, Northern Ireland had a session on the environmental effects of light at night (LAN). It dealt with bats, turtles, the "hidden" harms of LAN, and many other topics.<ref>[http://www.ustream.tv/recorded/2181927 Video] {{Webarchive|url=https://web.archive.org/web/20110102120622/http://www.ustream.tv/recorded/2181927 |date=2011-01-02 }}. Ustream.tv. Retrieved 2011-12-03.</ref> The environmental effects of LAN were mentioned as early as 1897, in a ''[[Los Angeles Times]]'' article. The following is an excerpt from that article, called "Electricity and English songbirds":

{{blockquote|An English journal has become alarmed at the relation of electricity to songbirds, which it maintains is closer than that of cats and fodder crops. How many of us, it asks, foresee that electricity may extirpate the songbird?{{nbsp}}... With the exception of the finches, all the English songbirds may be said to be insectivorous, and their diet consists chiefly of vast numbers of very small insects which they collect from the grass and herbs before the dew is dry. As the electric light is finding its way for street illumination into the country parts of England, these poor winged atoms are slain by thousands at each light every warm summer evening.{{nbsp}}... The fear is expressed, that when England is lighted from one end to the other with electricity the songbirds will die out from the failure of their food supply.<ref>{{cite news|title=Electricity and English songbirds|date=14 September 1897|work=[[Los Angeles Times]]}}</ref>}}

===Effect on astronomy===
[[File:Light pollution It's not pretty.jpg|thumb|The constellation [[Orion (constellation)|Orion]], imaged at left from dark skies, and at right from within the Provo/Orem, Utah metropolitan area.]][[Astronomy]] is very sensitive to light pollution. The [[night sky]] viewed from a city bears no resemblance to what can be seen from dark skies.<ref>{{cite web |url=http://ngm.nationalgeographic.com/2008/11/light-pollution/klinkenborg-text |archive-url=https://web.archive.org/web/20081018060653/http://ngm.nationalgeographic.com/2008/11/light-pollution/klinkenborg-text |url-status=dead |archive-date=October 18, 2008 |work=[[National Geographic]] |publisher=[[National Geographic Society]] |date=November 2008 |access-date=2011-12-03|title=National Geographic Magazine }}</ref> [[Skyglow]] (the [[Light scattering by particles|scattering of light]] in the atmosphere at night) reduces the contrast between stars and [[Galaxy|galaxies]] and the sky itself, making it much harder to see fainter [[Astronomical object|objects]].<ref>{{Cite web |title=Skyglow |url=https://www.johncbarentine.com/skyglow.html |access-date=2024-04-23 |website=John C. Barentine's Personal Website |language=en |archive-date=2024-04-23 |archive-url=https://web.archive.org/web/20240423205030/https://www.johncbarentine.com/skyglow.html |url-status=live }}</ref> This is one factor that has caused newer [[Telescope|telescopes]] to be built in increasingly remote areas.

Even at apparent clear night skies, there can be a lot of [[stray light]] that becomes visible at longer [[Exposure time|exposure times]] in [[astrophotography]]. By means of software, the stray light can be reduced, but at the same time, object detail could be lost in the image.<ref>{{Cite journal |last1=Reegen |first1=P. |last2=Kallinger |first2=T. |last3=Frast |first3=D. |last4=Gruberbauer |first4=M. |last5=Huber |first5=D. |last6=Matthews |first6=J. M. |last7=Punz |first7=D. |last8=Schraml |first8=S. |last9=Weiss |first9=W. W. |last10=Kuschnig |first10=R. |last11=Moffat |first11=A. F. J. |last12=Walker |first12=G. A. H. |last13=Guenther |first13=D. B. |last14=Rucinski |first14=S. M. |last15=Sasselov |first15=D. |date=2006-04-21 |title=Reduction of time-resolved space-based CCD photometry developed for MOST Fabry Imaging data |journal=Monthly Notices of the Royal Astronomical Society |volume=367 |issue=4 |pages=1417–1431 |doi=10.1111/j.1365-2966.2006.10082.x |doi-access=free |issn=0035-8711|arxiv=physics/0703153 }}</ref> The following picture of the area around the [[Pinwheel Galaxy]] (Messier 101) with the [[apparent magnitude]] of 7.5<sup>m</sup> with all stars down to an apparent magnitude of 10<sup>m</sup> was taken in [[Berlin]] in a direction close to the [[zenith]] with a fast lens (f-number 1.2) and an exposure time of five seconds at an [[exposure index]] of ISO 12800:{{clear}}
<gallery widths="540" heights="120" perrow="2" class="center" mode="packed" caption="Pinwheel Galaxy in stray light">
File:Streulichtfilterung.0.P1023258.jpg|Original shot: lower edge [[Eta Ursae Majoris|Alkaid]], right of center the double star [[Mizar]] with [[Alcor (star)|Alcor]] and right edge [[Epsilon Ursae Majoris|Alioth]]; the [[Pinwheel Galaxy]] is a small diffuse dot in the center of the image.
File:Streulichtfilterung.1.P1023258.jpg|Black level compensation: the darkest point in the digital picture was set to zero luminance, in order to reduce the visible stray light. However, blue light caused by [[Rayleigh scattering]] is visible in the center of the image.
File:Streulichtfilterung.2.P1023258.jpg|50 percent of stray light removed: the darker half of the stray light was set to zero luminance. The darker part of the blue light caused by Rayleigh scattering is still visible in the center of the image.
File:Streulichtfilterung.3.P1023258.jpg|Complete elimination of stray light: all pixels showing stray light have been set to zero luminance, the faint and two-dimensional Pinwheel Galaxy is no longer visible, too.
</gallery>

Some astronomers use narrow-band "[[astronomical filter|nebula filters]]", which allow only specific wavelengths of light commonly seen in [[nebula]]e, or broad-band "light pollution filters", which are designed to reduce (but not eliminate) the effects of light pollution by [[optical filter|filtering]] out [[spectral line]]s commonly emitted by [[sodium-vapor lamp|sodium]]- and [[mercury-vapor lamp]]s, thus enhancing contrast and improving the view of dim objects such as galaxies and nebulae.<ref>{{cite web |url=http://www.astronexus.com/node/4 |title=Use of light pollution filters in astronomy |publisher=Astronexus |access-date=2011-12-03 |archive-date=2011-11-12 |archive-url=https://web.archive.org/web/20111112081736/http://www.astronexus.com/node/4 }}</ref> Unfortunately, these light pollution reduction (LPR) filters are not a cure for light pollution. LPR filters reduce the brightness of the object under study and this limits the use of higher magnifications. LPR filters work by blocking light of certain wavelengths, which alters the color of the object, often creating a pronounced green cast. Furthermore, LPR filters work only on certain object types (mainly [[emission nebulae]]) and are of little use on galaxies and stars. No filter can match the effectiveness of a dark sky for visual or [[photographic filter|photographic]] purposes.
[[File:Milky Way Shines over Snowy La Silla.jpg|thumb|The [[Atacama Desert#Astronomical observatories|Atacama Desert]] in northern Chile is far from any cities, and the night sky there is pitch-black. Photo by José Francisco Salgado.<ref>{{cite web |title=Milky Way Shines over Snowy La Silla |url=http://www.eso.org/public/images/potw1319a/ |work=ESO Picture of the Week |access-date=13 May 2013}}</ref>]]

Light pollution affects the visibility of [[deep-sky object|diffuse sky objects]] like nebulae and galaxies more than stars, due to their low surface brightness. <ref>{{Cite journal |last=Varela Perez |first=Antonia M. |date=2023-06-16 |title=The increasing effects of light pollution on professional and amateur astronomy |url=https://www.science.org/doi/10.1126/science.adg0269 |journal=Science |language=en |volume=380 |issue=6650 |pages=1136–1140 |doi=10.1126/science.adg0269 |pmid=37319198 |bibcode=2023Sci...380.1136V |issn=0036-8075 |access-date=2024-04-23 |archive-date=2024-04-24 |archive-url=https://web.archive.org/web/20240424040546/https://www.science.org/doi/10.1126/science.adg0269 |url-status=live }}</ref> Most such objects are rendered invisible in heavily light-polluted skies above major cities. A simple method for estimating the darkness of a location is to look for the [[Milky Way]], which from truly dark skies appears bright enough to cast a shadow.<ref>{{cite APOD |date=23 August 2010 |title=A Milky Way Shadow at Loch Ard Gorge |access-date=2011-12-03}}</ref>

In addition to skyglow, light trespass can impact observations when artificial light directly enters the tube of the telescope and is reflected from non-optical surfaces until it eventually reaches the [[eyepiece]]. <ref>{{Cite journal |last=Stone |first=Richard |date=2010-08-27 |title=Astronomers Hope Their Prize Telescope Isn't Blinded by the Light |url=http://dx.doi.org/10.1126/science.329.5995.1002 |journal=Science |volume=329 |issue=5995 |pages=1002 |doi=10.1126/science.329.5995.1002 |pmid=20798287 |bibcode=2010Sci...329.1002S |issn=0036-8075}}</ref> This direct form of light pollution causes a glow across the [[field of view]], which reduces contrast. Light trespass also makes it hard for a visual observer to become sufficiently adapted to the dark. The usual measures to reduce this glare, if reducing the light directly is not an option, include [[flocking (texture)|flocking]] the telescope tube and accessories to reduce reflection, and putting a light shield (also usable as a [[dew shield]]) on the telescope to reduce light entering from angles other than those near the target. Under these conditions, some astronomers prefer to observe under a black cloth to ensure maximum [[adaptation (eye)|adaptation]] to the dark.

===Increase in atmospheric pollution===

A study presented at the [[American Geophysical Union]] meeting in [[San Francisco]] found that light pollution destroys [[nitrate]] [[Radical (chemistry)|radicals]] thus preventing the normal night time reduction of atmospheric smog produced by fumes emitted from cars and factories.<ref>{{cite news | url=https://www.bbc.co.uk/news/science-environment-11990737 | work=BBC News | title=City lighting 'boosts pollution' | date=2010-12-14 | access-date=2018-06-22 | archive-date=2021-06-03 | archive-url=https://web.archive.org/web/20210603043113/https://www.bbc.co.uk/news/science-environment-11990737 | url-status=live }}</ref><ref>{{cite web | url=http://www.agu.org/cgi-bin/SFgate/SFgate?language=English&verbose=0&listenv=table&application=fm10&convert=&converthl=&refinequery=&formintern=&formextern=&transquery=au%3dstark&_lines=&multiple=0&descriptor=%2fdata%2fepubs%2fwais%2findexes%2ffm10%2ffm10 | title=Nighttime photochemistry: Nitrate radical destruction by anthropogenic light sources }}{{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> The study was presented by Harald Stark from the [[National Oceanic and Atmospheric Administration]].

===Reduction of natural sky polarization===

[[File:Effect of light pollution on sky polarization.jpg|thumb|Light pollution is mostly unpolarized, and its addition to moonlight results in a decreased polarization signal.]]

In the night, the polarization of the moonlit sky is very strongly reduced in the presence of [[Urban area|urban]] light pollution, because scattered urban light is not strongly polarized.<ref>{{cite journal|last1=Kyba|first1=C. C. M.|author2=Ruhtz, T.|author3=Fischer, J.|author4=Hölker, F.|title=Lunar skylight polarization signal polluted by urban lighting|journal=Journal of Geophysical Research|date=17 December 2011|volume=116|issue=D24|pages=D24106|doi=10.1029/2011JD016698|bibcode=2011JGRD..11624106K|url=http://www.slideshare.net/sacani/lunar-skylight-polarization-signal-polluted-by-urban-lighting|access-date=2014-02-21|doi-access=free|archive-date=2017-02-02|archive-url=https://web.archive.org/web/20170202050536/http://www.slideshare.net/sacani/lunar-skylight-polarization-signal-polluted-by-urban-lighting|url-status=live}}</ref> Polarized moonlight cannot be seen by humans, but is believed to be used by many animals for navigation.

===Economic relation===
It is not uncommon to find 24-hour business, such as gas stations, convenience stores, and pharmacies. Hospitals and other healthcare facilities must be staffed 24 hours per day, seven days per week. With the rise of Amazon, many factories and shipping companies now operate 24x7 shifts to keep up with the demand of the new global consumer. These industries all require light, both inside and outside their facilities to ensure the safety of their workers as they move about their jobs and when the enter and depart the facilities. As a result, "40% of the United States and almost 20% of the European Union population has lost the ability to view the night sky…in other words, it is as if they never really experience nighttime."<ref name="Cinzano-2001" />

With a focus on shift work and the continued need for 24-hour operations of specific sectors of the economy, researchers are looking at the impact of light pollution on this group of workers. In 2007 the International Agency for Research on Cancer (IARC) sought to bring notice to the risk from shift work as a probable risk for developing cancers.<ref>{{Cite journal |last1=Erren |first1=Thomas C. |last2=Falaturi |first2=Puran |last3=Morfeld |first3=Peter |last4=Knauth |first4=Peter |last5=Reiter |first5=Russel J. |last6=Piekarski |first6=Claus |date=24 September 2010 |title=Shift Work and Cancer |journal=Deutsches Ärzteblatt International |volume=107 |issue=38 |pages=657–662 |doi=10.3238/arztebl.2010.0657 |issn=1866-0452 |pmc=2954516 |pmid=20953253}}</ref> This move was the result of numerous studies that found increased risks of cancers in groups of shift workers. The 1998 Nurses Health Study found a link between breast cancer and nurses who had worked rotating night shifts in their young adult life.<ref>{{Cite journal |last1=Wegrzyn |first1=Lani R. |last2=Tamimi |first2=Rulla M. |last3=Rosner |first3=Bernard A. |last4=Brown |first4=Susan B. |last5=Stevens |first5=Richard G. |last6=Eliassen |first6=A. Heather |last7=Laden |first7=Francine |last8=Willett |first8=Walter C. |last9=Hankinson |first9=Susan E. |last10=Schernhammer |first10=Eva S. |date=2017-09-01 |title=Rotating Night-Shift Work and the Risk of Breast Cancer in the Nurses' Health Studies |url=https://academic.oup.com/aje/article/186/5/532/3852271 |journal=American Journal of Epidemiology |language=en |volume=186 |issue=5 |pages=532–540 |doi=10.1093/aje/kwx140 |issn=0002-9262 |pmc=5856106 |pmid=28541391 |access-date=2024-04-17 |archive-date=2024-04-14 |archive-url=https://web.archive.org/web/20240414043441/https://academic.oup.com/aje/article/186/5/532/3852271 |url-status=live }}</ref> However, it is not possible to halt shift work in these industries. Hospitals must be staffed around the clock.

Research suggests that, like other environmental issues, light pollution is primarily a problem caused by industrialized nations. Numerous economic indicators have been examined to get a better sense of where light pollution was occurring around the globe.<ref name="Gallaway-2010">{{Cite journal |last1=Gallaway |first1=Terrel |last2=Olsen |first2=Reed N. |last3=Mitchell |first3=David M. |date=15 January 2010 |title=The economics of global light pollution |url=http://dx.doi.org/10.1016/j.ecolecon.2009.10.003 |journal=Ecological Economics |volume=69 |issue=3 |pages=658–665 |doi=10.1016/j.ecolecon.2009.10.003 |issn=0921-8009}}</ref> Countries with paved roads, an indicator of developed infrastructure, often had increased light pollution.<ref name="Gallaway-2010" /> Similarly, countries with a high rate of resource extraction also have high rates of light pollution. Also those with the highest GDP and high surface area described as urban and suburban also had the highest rates of light pollution.<ref name="Gallaway-2010" />

China is an emerging leader in industrial and economic growth. A recent study of light pollution using the Defense Meteorological Satellite Program Operational Linescan System (DMSL/OLS) found that light pollution is increasing over the eastern coastal cities but decreasing over the industrial and mineral extraction cities.<ref name="Han-2014"/> Specifically, urban areas around the Yangtze River delta, Pearl River delta, and Beijing-Tianjin area are specific light pollution areas of concern.<ref name="Han-2014" /> Examining China as a whole, it was found that light pollution in the East and North was much higher than the West. This is consistent with major industrial factories located in the East and North while resource extraction dominates the West.<ref name="Han-2014" />

In 2009, following the United Nations declaration of ''The Year of Astronomy,'' researchers urged a better understanding of artificial light and the role it plays in social, economic, and environmental issues.<ref name="Hölker-2010">{{Cite journal |last1=Hölker |first1=Franz |last2=Moss |first2=Timothy |last3=Griefahn |first3=Barbara |last4=Kloas |first4=Werner |last5=Voigt |first5=Christian C. |last6=Henckel |first6=Dietrich |last7=Hänel |first7=Andreas |last8=Kappeler |first8=Peter M. |last9=Völker |first9=Stephan |last10=Schwope |first10=Axel |last11=Franke |first11=Steffen |last12=Uhrlandt |first12=Dirk |last13=Fischer |first13=Jürgen |last14=Klenke |first14=Reinhard |last15=Wolter |first15=Christian |date=2010 |title=The Dark Side of Light: A Transdisciplinary Research Agenda for Light Pollution Policy |url=http://dx.doi.org/10.5751/es-03685-150413 |journal=Ecology and Society |volume=15 |issue=4 |doi=10.5751/es-03685-150413 |issn=1708-3087}}</ref> Continued unfettered use of artificial light in urban and rural areas would cause a global shift with unpredictable outcomes. Focusing on the economic impact of increased energy consumption in light bulbs, or the move to energy efficiency of lighting, is not enough. Rather, the broader focus should be on the socio-economic, ecologic, and physiologic impacts of light pollution.<ref name="Hölker-2010" /> 

Humans require some artificial night light for shift work, manufacturing, street safety, and nighttime driving and research has shown that artificial light disrupts the lives of animals. However, recent studies suggest that we may be able to find a happy medium. A 2021 article examined seasonal light changes and its effect on all animals, but specifically mollusks.<ref name="Hussein-2020">{{Cite journal |last1=Hussein |first1=Ahmed A. A. |last2=Bloem |first2=Erik |last3=Fodor |first3=István |last4=Baz |first4=El-Sayed |last5=Tadros |first5=Menerva M. |last6=Soliman |first6=Maha F. M. |last7=El-Shenawy |first7=Nahla S. |last8=Koene |first8=Joris M. |date=2020-12-19 |title=Slowly seeing the light: an integrative review on ecological light pollution as a potential threat for mollusks |url=http://dx.doi.org/10.1007/s11356-020-11824-7 |journal=Environmental Science and Pollution Research |volume=28 |issue=5 |pages=5036–5048 |doi=10.1007/s11356-020-11824-7 |pmid=33341922 |pmc=7838132 |issn=0944-1344}}</ref> The article claims that previous light research primarily focuses on length of exposure to light.<ref name="Hussein-2020" /> However, further research should attempt to determine the safest amount of light exposure, in terms of duration and intensity, that would be most desirable for both humans and animals.<ref name="Hussein-2020" /> With the development on this data, possible safety limits could be applied for light levels.<ref name="Hussein-2020" /> Ideally, the light level would maintain human benefits, while also decreasing or fully removing the negative impacts on animals.

=== Noctalgia ===
Noctalgia is the feeling of loss of access to seeing a starry [[night sky]]. This also includes the feeling of "sky grief", where people no longer have the ability to look at the stars, something that has been done for most of human existence.<ref>{{Cite magazine |last1=Sutter |first1=Paul |author2=Space.com |date=2023-09-26 |title=The Loss of Dark Skies Is So Painful, Astronomers Coined a New Term for It |url=https://www.scientificamerican.com/article/the-loss-of-dark-skies-is-so-painful-astronomers-coined-a-new-term-for-it1/ |access-date=2023-10-20 |magazine=[[Scientific American]] |language=en |archive-date=2023-10-23 |archive-url=https://web.archive.org/web/20231023194331/https://www.scientificamerican.com/article/the-loss-of-dark-skies-is-so-painful-astronomers-coined-a-new-term-for-it1/ |url-status=live }}</ref> The phenomenon also includes the grief over not being able to have the sense of awe and wonder that humans often experience when stargazing.

Coined by Aprana Venkatesan of the University of San Francisco and John Barentine, an astronomer, the term first appeared in August 2023 as a response to an article on the effects of light pollution published in the journal [[Science (journal)|Science]].<ref name="Noctalgia eLetter">{{Cite journal |last1=Venkatesan |first1=Aprana |last2=Barentine |first2=John |date=2023-08-27 |title=Noctalgia (sky grief): Our Brightening Night Skies and Loss of Environment for Astronomy and Sky Traditions |url=https://www.science.org/doi/10.1126/science.adi4552 |access-date=2023-10-22 |journal=Science ELetters |volume=380 |issue=6650 |pages=1116–1117 |doi=10.1126/science.adi4552 |pmid=37319220 |language=en |arxiv=2308.14685 |bibcode=2023Sci...380.1116S |archive-date=2023-10-22 |archive-url=https://web.archive.org/web/20231022060452/https://www.science.org/doi/10.1126/science.adi4552 |url-status=live }}<!-- As of 2023-10-22, scroll down to the eLetters section for the source in question; no direct URL or anchor found other than the arXiv one. --></ref> Venkatesan and Barentine presented an all-encompassing definition that includes the loss of cultural identity and practices, such as [[storytelling]] and [[stargazing]], as well as ancient knowledge such as [[celestial navigation]].<ref>{{Cite web |date=2023-10-04 |title=Sky grief |website=Borneo Bulletin Online |agency=[[Agence France-Presse]] |url=https://borneobulletin.com.bn/sky-grief/ |access-date=2023-10-20 |language=en-US |archive-date=2023-10-23 |archive-url=https://web.archive.org/web/20231023194332/https://borneobulletin.com.bn/sky-grief/ |url-status=live }}</ref> The authors argued that the night sky deserves a global protection scheme as an important part of the global heritage.<ref name="Noctalgia eLetter" />