Light pollution : mitigation measures for environmental protection.
Date: 2023-11-15
Institutions: Directorate-General for Environment
Subjects: environmental impact, environmental protection, health risk, lighting, lighting equipment, nuisance, pollution, sustainable development, urbanisation

Science for Environment Policy

FUTURE BRIEF:
Light Pollution: Mitigation 
measures for environmental 
protection

November 2023
Issue 28

Environment

2

Science for Environment Policy
Light Pollution: Mitigation measures for environmental protection

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Acknowledgements
Printed by the Publications Office of the European Union in Luxembourg
We wish to thank the scientific advisor, Annika Jägerbrand (Assistant Professor in Biology, Gävle 
University, Sweden), for her input to this report

The contents and views included in Science for Environment Policy 
are based on independent research and do not necessarily reflect the 
position of the European Commission.

This Future Brief is written 
and edited by the Science 
Communication Unit, University 
of the West of England (UWE), 
Bristol.  
Email: sfep.editorial@uwe.ac.uk

To cite this publication:

Science for Environment Policy 
(2023) Light Pollution: Mitigation 
measures for environmental 
protection. Future Brief 28. 
Brief produced for the European 
Commission DG Environment 
by the Science Communication 
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Science for Environment Policy 
Future Brief 28:
Light Pollution: Mitigation measures 
for environmental protection

4

Contents

1. 

Introduction  

2.  Multi-scale transdisciplinary approaches to protect the environment  

from artificial light at night (ALAN) 

2.1.  Applying the precautionary principle to ALAN 

2.2.  Technological and practical adaptations of lighting design 

2.2.1.  Type of light source 

2.2.2.  Direction of light and shielding 

2.2.3.  Limitation on upward (or downward) light 

2.2.4.  Lighting control and adaptive lighting 

2.2.5.  Adaptive lighting: Smart, intelligent and nano approaches 

2.3.  Thresholds of artificial light to eliminate environmental harm  

2.3.1.  Lighting measurements and assessment  

2.4.  Management interventions and best practice for mitigating ALAN  
        impacts on the environment  

2.4.1.  Lighting masterplan and efficient design  

2.4.2.  Environmental lighting zones 

2.4.3.  Definition of ALAN-free areas and ecosystems 

2.4.4.  Dark infrastructure  

2.4.5.  Sustainable development / Multifunctionality of dark infrastructure  

2.4.6.  Cross-cutting approaches focussed on species and ecosystems 

3.  Monitoring ALAN remotely 

3.1.  Making sense of data with citizen science 

4.  Emerging issues in improving research approaches to ALAN,  

and knowledge gaps on impacts and mitigation  

4.1.  Establishing standardised thresholds, measurement protocols and mitigation guidelines 

4.2.  Interdisciplinary research on the effectiveness of measures  
        for mitigating the impacts of ALAN 

4.3.  Species for which the impact of ALAN is not known 

4.4.  Marine and Freshwater habitats lacking ALAN data 

4.5.  Geographical disparities in impacts of ALAN 

5.  Summary and conclusions 

References  

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Artificial lighting can cause light pollution, which is recognised as one of 
the most complex environmental degradation forms of the 21st century. 
Despite the need for night-time lighting, light pollution presents a severe 
problem for the environment and humankind. It can have adverse effects 
on people, astronomy and wildlife health, and results in inefficient use 
of energy and other environmental harm (e.g. carbon dioxide emissions, 
global warming), crime and disorder.

Katja Emen, Faculty of Criminal Justice and Security; University of Maribor. Slovenia, 2021

1. 

Introduction 

The  growing  world  population,  coupled  with 
increasing  urbanisation,  has  led  to  increased 
use  of  artificial  lighting  inside  buildings,  but  also 
outdoors at night-time. Light pollution occurs when 
the presence of artificial light produced by human 
activities adversely affects the natural environment 
and the health and well-being of living organisms, 
including humans. 

Lighting that causes light pollution is often referred 
to  by  the  umbrella  acronym  ‘ALAN’,  referring  to 
artificial light at night1. For most of human history 
we have used candles to light our way with sunset 
and sunrise marking the decreases and increases 
in  our  activity  levels.  However,  the  advent  of 
electrical  outdoor  lighting  has  changed  these 
activity  patterns.  Although  this  has  led  to  many 

benefits,  it  also  means  that  for  most  people  the 
night  sky  is  no  longer  dark,  and  they  cannot  see 
the Milky Way (Smith et al., 2023). 

ALAN  has  largely  increased  overtime  due  to 
industrialisation,  urbanisation  and  population 
growth.  However,  the  recent  focus  on  energy 
efficiency  to  tackle  climate  change,  as  well  as 
to  lower  the  rising  cost  of  energy,  has  led  to 
technologies and behaviour changes by consumers 
that  also  lower  light  pollution  (Jägerbrand  and 
Spoelstra,  2023).  LED  technology  for  example, 
is more energy efficient and when used correctly 
can  lead  to  less  light  pollution  than  older  light 
sources;  however,  the  colour  emitted,  necessity, 
timing,  positioning  and  shielding  should  all  be 
considered carefully.

1 

Please note that ‘artificial light at night’, is still the same type of ‘natural light’ as during the day i.e. photons, but the light source 
is electric, and it is this source that is artificial.

7

Figure 1: Maps depicting truly dark spaces in the EU-38 in 2014–2015, on the left-hand side (71.3%), versus 
in 2020–2021 (66.1%). These show an approximate loss of 5% of truly dark spaces across Europe in six years. 
This image is created from remote sensing imagery by the VIIRS Satellite. Black denotes ‘truly dark’ spaces 
which, in this image, is suggested to be European land surface with light emissions below or equal to 0.5 nW/
cm2/sr (nanowatts per square centimetre per steradian) of radiance. Blue denotes European land surface where 
light emissions are higher than 0.5 nW/cm2/sr. Exclusion of Northern region depicted in white due to confounding 
effect of Aurora lights (Widmer et al., 2022). Source: European Topic Centre on Human Health and Environment 
on behalf of EEA, 2022.

The  principle  focus  of  this  brief  is  the  environmental 
impact of artificial light at night. However, ALAN can also 
affect human health, with evidence that exposure to light 
at night can lower melatonin production, resulting in sleep 
deprivation, fatigue, headaches, stress, anxiety and other 
health problems. Some studies also show a correlation 
between reduced melatonin levels and cancer. 

Humans are adapted to being active during the day, so 
our visual system requires greater luminance than species 
adapted  to  being  active  at  night.  Light  pollution  occurs 
as an unwanted side effect of people using lighting to be 
safely  active  outdoors  at  night.  There  is  some  evidence 
that inadequate lighting can contribute to people feeling 
anxious due to fear of attack, physically hurting themselves 
due to poor visual perception, or being less physically active 
i.e. avoiding walking at night. In focusing on environmental 
impacts on non-human flora and fauna primarily, we are 
not ignoring human concerns, as mitigating for the negative 
impacts of ALAN for biodiversity, will benefit people both 
indirectly and directly.

ALAN  disrupts  ecosystems,  interferes  with  wildlife 
behaviour  and  migration  patterns,  can  impact  human 
health, and obscures our view of the night sky. To address 
these  concerns,  this  report  aims  to  introduce  various 
mitigation measures that can be implemented to protect 
the environment from light pollution. 

To  provide  some  essential  background  knowledge  this 
brief will present an initial overview of the types of light 
pollution  and  some  of  their  impacts  on  wildlife,  and 
ecosystems. This will be followed by a brief exploration of 
ways to measure light pollution when investigating ALAN 
at different scales in the environment. 

As  with  many  emerging  environmental  threats,  the 
research evidence on the impacts of ALAN on different 
groups of organisms is still in its infancy, however, there 
is sufficient evidence to suggest it may have some quite 
significant  detrimental  impacts  on  biodiversity  and 
human health. A consideration regarding application of 
the precautionary principle will be provided at the outset. 

The  majority  of  this  report  will  explore  multiscale 
transdisciplinary approaches to protect the environment 
from  ALAN.  This  will  firstly 
innovative 
technological and practical adaptions of lighting design, 
to  mitigate  negative  impacts  on  the  environment. 
Management interventions and best practice approaches 
to mitigate impacts will be presented in the second half 
of chapter 2. 

introduce 

Mitigation measures can be introduced at different levels 
(stakeholders), across different sizes of spatial area, and 
for different times of the year/night to systematically deal 
with light pollution and its consequences. The concept of 
‘Dark Infrastructure’ to be used alongside, in conjunction 

8

with,  or  as  an  add-on  to  existing  blue  and  green 
infrastructure  is  presented.  Dark  infrastructure  creates 
dark  corridors,  enabling  movement  of  photo-sensitive 
species through an area of continuous darkness. 

Legislative  approaches  are  an  important  aspect  of 
strategies  and  measures  to  manage  the  ecological 
impact  of  ALAN,  alongside  technical  and  practical 
adaptations used in cross cutting approaches at species, 
taxa, or area/ecosystem scale (see Table 1) (Jägerbrand 
and Bouroussis, 2021(a); Rodrigo-Comino  et al., 2021; 
Morgan-Taylor, 2023). 

In  this  report  we  will  focus  on  categories  3  (adaption 
to  lighting  design  to  mitigate  ALAN)  and  4  (measures 
targeted at certain sensitive habitats or taxa) from table 1, 
as well as discussing some category 2 current mitigation 
efforts undertaken by local government and communities 
in towns and cities. Legislative approaches to ALAN can 
be reviewed in a recent report by Widmer et al., 2022, with 
an emphasis placed on identifying appropriate thresholds 
levels of ALAN for regulatory purposes (Widmer et al., 
2022).  However,  it  must  be  remembered  that  none  of 
these measures will work in isolation and they need to 
be  implemented  in  combination,  strategically  and  with 
stakeholder input. 

Table 1: Division in groups for measures for reducing the adverse effects of ALAN, adapted from Jägerbrand 
and Bouroussis (2021a)

Category

Examples of recommendations

1.  Recommendations  for  legislation  at  national 
or international levels

Classification  of  ALAN-free  zones,  limits  of 
upward  emitted  light  over  geographical  areas, 
legislation limiting the negative impact of ALAN.

2.  Recommendations  for  practical  schemes 
at  local  government  level  in  cities,  towns  and 
villages.

Combining measures to reduce energy use and 
limit ALAN by integrating smarter lighting design, 
for  example,  sensors  that  turn  on  lights  in  car 
parks, or on pathways in parks only when people 
approach. Retrofitting shielded luminaires to limit 
light  spill.  Using  timers  to  reduce  unnecessary 
light at times when it isn’t needed. Sustainable 
lighting to reduce energy costs and CO2 output 
whilst minimising impact of ALAN.

3. Recommendations for technical and practical 
adaptations of the lighting design

Precise lighting design: spectral power distribution, 
lighting  control  and  adaptive  lighting  concepts, 
light distribution and orientation.

4. Recommendations for sensitive species, taxa, 
or ecosystems

Measures  for  reducing  impacts  on  sensitive 
species  and  habitats,  identifying  species  and 
groups  that  are  sensitive  and  suggesting 
management  of  sensitive  areas  to  avoid  the 
impact of ALAN.

A range of inspirational case studies of successful 
to  ameliorate 
use  of  mitigation  measures 
negative impacts of ALAN on biodiversity will be 
provided in this brief. With examples of successful 
mitigation  measures  used  for  more  photo-
sensitive  nocturnal  and  twilight  active  species, 
and  taxa  impacted  by  ALAN,  such  as  migratory 

birds, turtle hatchlings, bats and nocturnal insects.  
More widespread use of such mitigation measures, 
through partnerships that enable comprehensive 
strategies  to  be  implemented,  would  contribute 
considerably  to  mitigating  the  present  upward 
trend of light pollution overtime and the inherent 
negative impacts.

9

Night image of Paris, France, from the International Space Station by NASA Wikimedia Commons CC By 4.0.

Pursuing zero pollution, including in relation to harmful chemicals, in 
order to achieve a toxic-free environment, including for air, water and 
soil, as well as in relation to light and noise pollution, and protecting 
the health and wellbeing of people, animals and ecosystems from 
environment-related risks and negative impacts

Light pollution in the 8th Environment Action Programme’s priority objectives 

 
10

2.  Multi-scale transdisciplinary approaches to protect 
the environment from artificial light at night (ALAN)

The  impact  of  artificial  light  on  the  environment 
is  multifaceted  and  complex.  Although  there  is 
consensus  from  the  scientific  community  that 
ALAN is an issue that needs to be addressed, the 
scientific sources behind this consensus are diverse 
in their disciplines and their approaches to study. 

Studies  can  focus  on  different  impacts  of  light 
pollution (e.g. astronomical, ecological and human 

health) (Jägerbrand, 2022) and on different types 
of  light  that  can  contribute  to  light  pollution, 
such  as  skyglow  and  spill  light  (see  box  1)  (CIE, 
2020). Research in this area uses distinct methods 
or  approaches  to  measure  impacts  (e.g.  remote 
sensing  techniques,  surveys,  laboratory  analysis, 
modelling  tools)  and  considers  different  scales 
in  time  and  space  (Rodrigo-Comino  et  al.,  2021; 
Kocifaj et al., 2023).

Box 1: Description of different types of light pollution

(International Dark Sky Association - https://www.darksky.org/light-pollution/; 
International Commission on Illumination (CIE ) - https://cie.co.at/eilvterm/17-29-185):

 y Glare – excessive brightness (luminance) that 
causes visual discomfort or a reduction in the 
ability to see objects (known to effect humans, 
paucity of research on other species).

 y Skyglow – brightening of the night sky over 
inhabited areas from reflected light scattered 
by the atmosphere.

 y Clutter – bright, confusing and excessive 
groupings of light sources (known to effect 
humans; paucity of research on other species).

 y Reflected light - reflected light from nearby 

surfaces is spread in different directions 
around the lighting installation.

 y Spill light - light emitted outside the area 
that a lighting installation is designed to 
illuminate, onto adjacent areas where it is 
unnecessary.

Skyglow from urban area lighting up the night sky.  
Source: https://www.pexels.com/photo/green-leafed-plants-under-starry-night-1676073/ 

11

Figure 2: Types of obtrusive light. Spill light is the light emitted by a lighting installation that falls beyond the 
intentionally lit area. Source:  Annika Jägerbrand

Figure 3. Infographic illustrating the impact of light pollution on our ability to see stars and other objects in the 
night sky. The numeric scale is similar to that used by citizen scientists on the ‘Globe at Night’ project, run by 
the National Science Foundation’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory), which 
concludes that stars are disappearing from human sight at an astonishing rate. Source: NOIRLab/NSF/AURA, P. 
Marenfeld, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons.

 
12

In  addition  to  this,  those  involved  in  decision-
making  have  different  perspectives,  depending 
on whether they are scientific or industry experts, 
policymakers  or  the  public.  Within  these  groups 
there  are  differing  priorities,  such  as  ecological 
protection, protection of astronomical observations 
from  Earth,  energy  efficiency  and  public  safety  – 
all of which consider different measures of impact 
(Jägerbrand, 2022).

This  complexity  makes  it  challenging  to  mitigate 
for and prevent the impacts of ALAN, as there are 
a range of possible qualities to consider, measure 
and limit. It also necessitates interdisciplinary and 
joint  efforts  to  develop  and  implement  solutions. 
Experts from lighting, medical, and environmental 
research  communities  need  to  collaborate  across 
relevant  fields  (United  Nations  Office  for  Outer 
Space Affairs, 2021).

These collaborations have produced initiatives and 
techniques  to  manage  light  pollution  that  span 
across  technical  innovation,  regional,  national 
initiatives  and  approaches 
and 

international 

focused  on  species  or  ecosystems  (Widmer  et 
al.,  2022).  For  example,  the  recent  ‘responsible 
outdoor  lighting  at  night’  (ROLAN)  manifesto 
came  out  of  the  ROLAN  conference  that  was 
organised by the ILLUME research group from the 
Gdansk  University  of  Technology,  and  the  Society 
of  Light  and  Lighting  (SLL).  It  provides  10  core 
principles  for  external  illumination,  with  easy-to-
follow  actions  to  minimise  the  impact  of  outdoor 
night-time  lighting  and  make  the  stars  visible 
again, and has been adopted by the International 
association  of  lighting  designers  (IALD)  and  the 
Illuminating Engineering Society IES, showing dark 
sky  protection  is  underway  (International  Dark-
Sky  Association,  2023;  Zielinska-Dabkowska,  et 
al.,  2023).  However,  the  implementation  of  these 
new  approaches  remains  low,  (Rodrigo-Comino  et 
al., 2021) and tends to consider only one or a few 
aspects  of  ALAN  and  their  impacts  in  isolation. 
There  is  a  need  for  more  evaluation  and  greater 
knowledge  sharing 
to  develop  multifaceted 
solutions to this complex problem. 

2.1.  Applying the precautionary principle to ALAN

impact  and 

There  is  a  paucity  of  empirical  data  on  the  effects 
of  ALAN,  and  there  is  much  to  learn  about  the 
relationships  between 
levels, 
spectral  content  and  directionality.  Consequently,  it 
has been recommended that precautionary methods 
are  implemented  to  avoid  and  mitigate  for  light 
pollution  in  protected  areas  (Commonwealth  of 
Australia, 2020;  Jägerbrand and Bouroussis, 2021b). 

light 

The  precautionary  principle  has  four  central 
components: taking preventive action in the face 
of uncertainty; shifting the burden of proof to the 
proponents of an activity; exploring a wide range 
of  alternatives  to  possibly  harmful  actions;  and 
increasing public participation in decision making 
(Science for Environment Policy, 2017; Kriebel et. 
al., 2001).

translate 

the  precautionary  principle 

To 
into 
approaches  to  reduce  ALAN,  organisations  and 
experts  working  in  this  area  have  proposed  simple 
rules.  For  example,  the  ‘UK  Dark  Skies  at  Night 
Partnership’ (UKDSP) is a collaborative forum of UK 
dark-sky  places,  including  those  with  International 
Dark-Sky  Association  designations;  the  Commission 

for  Dark  Skies;  the  Countryside  Charity  (CPRE);  the 
Institution of Lighting Professionals and the Society 
of Light and Lighting. The UKDSP has drafted a ‘Dark 
Sky Standard’ with its strategy having four pillars at 
its core described as “The right light, at the right place, 
at  the  right  amount,  for  the  right  duration”  (United 
Nations Office for Outer Space Affairs, 2021; UKDSP, 
2021),  where  the  expression  “right  light”  relates  to 
an  adequate  visual  performance  for  humans,  while 
meeting  the  goals  for  environmental  and  health 
protection.

Similarly, Clanton formulated an approach to reducing 
light pollution which involves (i) using lights only when 
necessary;  (ii)  employing  the  lowest  illuminance  as 
possible; and (iii) minimising the light shed skywards 
(Clanton, 2014).

National  light  pollution  guidelines  in  Australia 
suggest  that  the  starting  point  for  all  lighting 
designs  should  be  natural  darkness,  and  that 
artificial  light  should  only  be  added  for  specific 
and  defined  purposes,  and  only  in  the  required 
location,  and  for  the  specified  duration  of  human 
use (Commonwealth of Australia, 2020). 

13

Dead insects trapped after being attracted by light in a lighting box hidden in the soil near a public monument. This is an example 
of  an  ecological  trap  caused  by  light  pollution.  Source:  Lamiot,  CC  BY-SA  3.0  <https://creativecommons.org/licenses/by-sa/3.0>,  via 
Wikimedia Commons

2.2.  Technological and practical adaptations of lighting design

researchers  have  argued 

Some 
that  older 
installations  of  night-time  lighting  systems  in 
the  United  States  are  inefficient,  overly  brilliant, 
improperly  directed  and  shielded;  some  being 
entirely  unnecessary  (Nguyen  and  Gupta,  2022). 
Unshielded light fixtures can direct more than half 
of  their  illumination  upward  or  laterally,  resulting 
in  only  40%  of  the  light  illuminating  the  ground 
(Nguyen  and  Gupta,  2022).  In  some  parts  of  the 
world nearly a third of outdoor lighting is projected 
to be wasted as a result of this poor design. 

There have been huge technological and innovative 
advances  in  lighting  design  that  have  improved 
energy efficiency, aesthetics and functionality. This 
has happened both for outdoor and indoor lighting, 
and with both positive and negative consequences 
for  the  environment  in  terms  of  light  pollution. 
Technology in this field continues to progress and 
is becoming increasingly informed by research into 
the  impacts  of  ALAN.  The  ultimate  goal  is  that 
lighting  can  continue  to  fulfil  its  purpose,  while 
minimising or eliminating environmental harm.  

14

Table 2: Different general approaches to adapting lighting design

Focus of adaptation 

How it works

Modifying the light source

Changing colour, intensity

Changing the direction of light and shielding light

Using shielding or other approaches to prevent 
light from falling where it is not intended or 
needed

Limitation of upward and downward light

Reducing amount of light going upwards, 
particularly to reduce skyglow

Lighting control and scheduling

Scheduling light to be present only at times 
when it is needed

Smart, intelligent and nano approaches

Using IT solutions that connect light to 
customer needs through Internet of Things

2.2.1.  Type of light source

As  a  response  to  the  climate  crisis  and  energy 
lighting  strategies  are 
prices,  contemporary 
focusing  on  energy-efficient  systems  with  low 
carbon  output.  As  a  result,  many  countries  are 
transitioning  to  white  light  emitting  diodes  (LED), 
which  are  more  sustainable  than  sodium  vapour 
lights  as  they  require  less  energy,  however,  they 
have negative impacts on many living organisms. 
These white LEDs have a higher output of shorter 
wavelengths, emitting light in the blue part of the 
spectrum  (Widmer  et  al.,  2022).  Unfiltered  white 
light  LEDs  can  have  a  more  negative  ecological 
impact  on  certain  species  relative  to  lights  with 

other  colour  spectra.  So,  it  is  important  to  use 
these light sources carefully, after consideration of 
the need for ALAN, and where possible use lower 
intensity  LEDS  with  a  lower  blue  content  when 
possible.  Blue  wavelengths  affect  the  circadian 
rhythms of humans, insects and other vertebrates, 
largely because many organisms perceive shorter 
wavelengths of light, i.e. blue light, better than they 
can perceive light of longer wavelengths, meaning 
that the impacts of light pollution will be greater 
for  blue  light  compared  to  longer  wavelengths 
(Jägerbrand and Bouroussis, 2021b). 

Overview  of  the  type  and  colour  of  the  different 
wavelengths.  Source:  Tom  Gaimann,  CC  BY-SA  4.0 
<https://creativecommons.org/licenses/by-sa/4.0>, via 
Wikimedia Commons

15

Figure 4. Offshore oil and gas rigs and wind farms in the North Sea shine brightly on the water, as does the glow 
of coastal cities in, for example, the United Kingdom (landmass at left) and Norway (upper right). In April, the 
region’s  waters  are  clear  enough  that  the  artificial  light  can  penetrate  from  1  metre  depth  (dark  blue  in  the 
picture) to 30 metres depth (yellow in the picture). Source: NASA Earth Observatory images by Joshua Stevens, 
using data courtesy of Smyth, T.J., et al. (2021). 

Approaches to minimise and avoid blue content of 
light  have  been  recommended  and  implemented. 
These include filtering out wavelengths in the blue 
region or using yellow, green or amber LEDs. 

In  the  case  of  coastal  installations,  it  has  been 
suggested  that  using  red  artificial  light  at  night 
might  be  favourable  to  most  marine  organisms 

as this light wave colour weakens quickly in water 
and  so  doesn’t  penetrate  very  far  (Davies  et  al., 
2020).  Most  marine  species  are  not  sensitive  to 
this wavelength of light, as they have evolved in its 
absence, however, there are other considerations 
regarding  red  light  use  at  sea,  such  as  whether 
this  colour  of  light  would  still  serve  its  function 
for humans.

16

Box 2: Do red coloured LED lights in street lamps, cause less impact on 
wildlife than other LED colours?

Figure 5: Green light, white light, and red-light treatments in a natural area in the Netherlands – part of an 
experiment by Kamiel Spoelstra, of the Netherlands Institute of Ecology, to examine the impact of different 
spectra across multiple taxa, including birds, bats, and insects. Source: Photographs by Kamiel Spoelstra /
NIOO-KNAW

Kamel Spoelstra and colleagues have been running 
ALAN experiments in the Netherlands since 2010, 
examining the impacts of different colours of street 
lamp  lights  on  wildlife,  including  bats,  insects, 
mice,  voles  and  birds.  They  noted  that  the  least 
impactful colour of LED light was red light, where 
bat frequency and behaviour largely mimicked that 
of the dark control areas. 

In contrast, white and green light was found to be 
an ‘ecological trap’ for moths and other nocturnal 
insect  species,  i.e.  the  light  offers  a  seemingly 
attractive habitat for these species, but in reality 
compromises their survival. In this case the moths 
and  insects  were  attracted  to  the  lights,  and 
then  eaten  by  non-light-shy  bat  species,  such  as 
the  common  pipistrelle  (Pipistrellus  pipistrellus), 
which  took  advantage  of  the  abundance  of 
prey.  This  created  a  situation  where  the  insects 
were  initially  flying  much  higher  near  the  lights, 
but  over  time  this  abundance  fell  to  below  that 
noted  at  dark  or  red-light  lamp  posts.  Most 
bat  species  do  not  perceive  red  light  as  well  as 
blue  light,  explaining  the  reduced  impact  of  red 
light  on  their  behaviour  (Spoelstra  et  al.,  2017).  

However,  more  recent  studies  examining  the 
impacts  of  colour  spectra  of  ALAN  on  bat  flight 
behaviour  along  ecological  corridors  and  during 
migration, found some species of bats are impacted 
by both red and white spectra. For example, when 
red  or  white  light  was  placed  on  one  side  of  a 
hedgerow,  one  bat  species,  the  lesser  horseshoe 
bat, Rhinolophus hipposideros, was found to detour 
and fly along the other side, seeking shelter among 
vegetation  (Zeale  et  al.,  2018).  This  highlights 
the  issue  that  red  light  is  not  a  perfect  solution, 
but also that vegetation and orientation of street 
lighting  can  help  mitigate  the  impacts  of  ALAN 
when  lighting  is  unavoidable  (Barré  et  al.,  2021; 
Barré et al., 2023).

So, when a protected light-sensitive bat species is 
present, such as the rare lesser horseshoe bat, the 
use of light at night needs to be considered more 
carefully and mitigation measures put in place, or, 
ideally,  no  light  used  at  all.  In  the  UK  the  latest 
guidelines for developers, issued by the Institution 
of Lighting Professionals and the Bat Conservation 
Trust,  suggest  maintaining  dark  corridors 
in 
any  developments  near  to  lesser  horseshoe  bat 
foraging or roosting sites, with shielded red lighting 
near these corridors (ILP/BCT, 2023). 

Recent advances in tuneable white technology, and 
other combined sources with various spectra, offer 
the  flexibility  of  using  application-specific  light 
sources together with spectrum control over time. 
Tuneable liquid lenses, for example, have enabled 
the  development  of  luminaires  with  changeable 
beam  patterns,  focus  and  colour  temperature 
(Nguyen and Gupta, 2022). Researchers have also 
developed,  white  light  emitting  diodes  (WLEDs) 
that  have  the  same  intensity  as  traditional  LEDs 
but  provide  a  more  diffuse  light  with  less  glare 
and  hardly  any  blue  component.  These  WLEDs 
use layers of organic fluorescent dyes to perform 
spectral  conversion,  rather  than  phosphor,  and 
enable  accurate  colour  perception  compared  with 
natural light (Menéndez-Velázquez et al., 2022).  

and 

processes 

There  is  a  large  variability  in  photoreceptors, 
light-related 
photobiological 
behavioural responses across the bio-environment. 
Although  reducing  blue  content  is  expected  to  be 
helpful  in  many  cases,  there  is  no  best  spectrum 
for all applications, since different colours of light 
may  affect  species  in  different  ways  (Longcore, 
2023;  UN  Office  for  Outer  Space  Affairs,  2020). 
Despite this uncertainty, the consensus at present 
for  minimising  the  impact  of  ALAN  on  terrestrial 
species,  when  the 
light  cannot  be  removed 
completely is to use amber or red lights, with little 
or no blue. However, as there are some exceptions 
to this warmer colour change for some organisms 
(e.g.  horseshoe  bats),  as  discussed  in  Box  2,  it  is 
important to consider the specific qualities of the 
environment  with  regard  to  species  present,  and 
the  functional  need  of  humans  inhabiting  the 
space to ensure their safety. 

Researchers  have  developed  an 
index  based 
on  standard  spectral  emission  curves  for  new 
and  established  outdoor  lighting,  alongside  the 
spectral  response  curves  of  certain  organisms 
–  which  is  a  way  to  map  their  responses  over 
different  wavelengths.  This  index  provides  a  tool 
to  assess  the  potential  impact  of  lights,  in  terms 
of  how  well  the  light  is  perceived  by  organisms, 
if  at  all.  The  approach  can  be  updated  with  new 
information about both the spectral responses of 
organisms, and the emissions of light sources, and 
could  potentially  be  used  to  help  inform  choice 
about new lighting products (Longcore et al., 2018). 

17

There  is  however,  further  work  to  be  undertaken 
to investigate the effect that light intensity has in 
combination  with  spectral  output,  and  research 
is  ongoing  to  note  if  this  has  an  impact,  and  if 
so,  what  this  is.  Therefore,  future  adjustment  to 
the  index  may  be  required  as  new  research  data 
becomes available.

The  level  of  light  exposure  from  artificial  light 
sources at night is the most critical factor – if a light 
appears brighter, i.e. has greater illuminance, it will 
be  emitting  more  light  into  the  environment.  So, 
when installing lights, the important factor is not 
only the amount of blue light that is emitted, but 
also how bright it is – or its illuminance. If selecting 
an amber light source – as this has less negative 
ecological  impacts  than  a  blue  light  source  –it 
also needs to be of low brightness or illuminance. 
Ultimately,  the  critical  factor  is  the  level  of  light 
exposure  (brightness,  or  illuminance)  for  species 
or environments – shown by recent research that 
investigated the impact of light colour versus light 
intensity on glow-worm mate choice. The intensity 
of light interfered more with mate choice than the 
colour of the light (Van de Broeck, et al., 2021). 

When  choosing  light  sources  in  the  presence  of 
certain  species,  such  as  migratory  bird  species, 
turtle hatchlings, or bats, the overarching guidance 
is  to  choose  a  light  source  from  the  warmer  end 
of  the  colour  spectrum, 
i.e.  yellow/amber/red, 
with  most  or  all  of  the  blue  light  removed.  The 
International  Convention  on  the  Conservation  of 
Migratory  Species  of  Wild  Animals  (CMS)  provides 
more  specific  guidance  on  this.  However,  this  can 
be  summarised  as  allowing  high  or  low-pressure 
sodium lights, and, in some instances, filtered LEDs 
or metal halides which remove the red wavelength of 
light. Luminaires which should not be installed when 
these light-sensitive species are present, are those 
containing  blue  light  such  as  metal  halide,  white 
LED,  Halogen,  mercury  vapour,  white  fluorescent 
(CMS, 2023; Department of Climate Change, Energy, 
the Environment and Water, 2023). 

However, in the presence of these species, and as 
a  default  position  for  any  new  light  installation 
luminaires  should  only  be 
externally, 
installed  when  there  is  a  human  safety  need  for 
artificial light.

these 

18

2.2.2.  Direction of light and shielding

The direction of light is an important aspect that 
can affect if, and how, light pollution impacts the 
environment.  The  concept  of  spill  light  (see  box 
1) describes light falling where it is not intended, 
or needed, and there are techniques to reduce or 
eliminate this. 

Special  optics  is  the  primary  modern  solution  for 
ensuring only the intended area is lit, with designed 
optics  that  can  be  very  accurately  focused,  for 
example to shine only on a certain spot, or along 
roads  rather  than  across  them  (Wänström  Lindh 
and  Jägerbrand,  2021).  By  using  these  types 
of  optical  designed  solutions  there  is  very  little 
wasted light, and so less wasted energy. 

However,  when  it  comes  to  improving  existing 
light  installations,  retro-fitting  luminaires  with 
physical barriers known as shields can be useful in 
mitigating light spill as this blocks light from spilling 
beyond  certain  angles.  There  are  different  levels 
of shielding to enable the approach to be tailored 
to the situation, starting with sharp shielding that 
doesn’t  allow  any  luminous  flux  above  or  below 
the horizon, and less than 1 per cent of the total 
luminous flux between 80 and 90 degrees of the 
nadir (see figure 7). 

Figure 6. Lights should be directed towards the area intended to be lit, and shielded to further avoid lighting 
anything but the target area or object. Additional measures to ameliorate impacts of ALAN are warmer coloured 
luminaires, of lower intensity and set to only come on at required times. Source: DCCEEW 2023, National Light 
Pollution Guidelines for Wildlife, Department of Climate Change, Energy, the Environment and Water, Canberra, 
May. CC BY 4.0.

19

Figure 7: Example of shielding of luminaires to reduce 
ecological light pollution in protected areas: (A) sharp 
cut-off,  SCO  (B)  BUG  system  (not  to  scale).  Source: 
Jägerbrand and Bouroussis, 2021b

Another  approach  is  the  BUG  system  that  allows 
stricter and more detailed shielding. The acronym 
stands for backlight, uplight and glare (see figure 
7 and box 3) It is recommended to keep uplight as 
close to zero as technically possible and backlight 
as  low  as  possible  in  protected  areas  to  prevent 
light pollution and skyglow.

Image depicting road lighting on a rural street with some shielding 
of  the  luminaire.  Lights  should  be  directed  towards  the  area 
intended to be lit, and shielded to further avoid lighting anything 
but  the  target  area  or  object.  Additional  measures  to  ameliorate 
impacts of ALAN are warmer coloured luminaires, of lower intensity 
and  set  to  only  come  on  at  required  times.  Source:  Shutterstock, 
photo by Amy Johansson

In the European Union, lighting accounts for 14% of total energy 
consumption; of that, approximately 14.7% is outdoor stationary lighting, 
which are mainly streetlights. Globally, almost one-fifth of all electricity 
produced is used for lighting, of which approximately 8% is outdoor 
stationary lighting

Source: De Almeida et al., 2014

 
 
20

A: Road 
lighting

B: Bridge 
lighting

C: Aesthetic 
lighting

D: Façade 
lighting

E: Sky  
glow

Examples of affected taxa

Bats

Insects

Amphibians

Mammals

Birds

Spiders

Fish

Birds

Bats

Amphibians

Insects

Insects

Bats

Birds 

Spiders

Bats

Insects

Mammals

Birds

Spiders

Fish

Insects

Shellfish

Bats

Turtles

Examples of mitigation measures

•  Luminaire 
shielding

•  Improved 
optics

•  Adaptive 
lighting

•  Physical 
barriers

•  Restrict spill 

light outside of 
bridge

•  Adaptive 
lighting

•  Remove 

aesthetic 
lighting from 
trees

•  Time-schedule 
for winter use

•  Replace with 
downward 
light

•  Bat presence: 
remove or 
do not use 
lighting

•  Adaptive 
lighting

•  Prevention of 
upward light 
via luminaire 
shielding or 
improved 
optics

•  Adaptive 
lighting

Figure 8: Examples of outdoor lighting installations, affected biodiversity groups, and some potential 
mitigation measures.

Photo A, depicts road lighting which can affect terrestrial species due to light spill. 

Photo B, shows bridge lighting spilling onto the harbour waters below, affecting terrestrial and aquatic species. 

Photo C, aesthetic lighting on trees affect species living in them and those that forage on them. This lighting should be removed or time 
restricted.

Photo D, upward façade lighting can affect several terrestrial species including bats, and it should be removed or replaced with 
downward lighting. 

Photo E, skyglow. Source: Figure adapted from Jägerbrand and Spoelstra 2023.

Photo  sources:  A:  Night  Highway  Light  Streetlights  Plumes  Headlights  Stock  Photo  1979678945  |  Shutterstock  ;  B:  Chris  Gin  from 
Auckland, New Zealand, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons; C: https://www.shutterstock.
com/image-photo/illuminated-trees-houses-summer-party-holiday-1763294753;  D:  Shashank  Verma,  Poland,  A  Hotel  Building  with 
Lights at Night · Free Stock Photo (pexels.com); E: City Night Stock Photo 695937 | Shutterstock

21

Box 3: BUG  (Firstlight Technologies)

The  BUG  rating  considers  Backlight,  Uplight,  and 
Glare.  BUG  was  developed  by  the  Illuminating 
Engineering  Society  (IES)  and  the  International 
Dark  Sky  Association  to  better  explain  how  light 
can  be  measured.  The  BUG  rating  of  a  luminaire 
relates to how much light a light fixture produces. 
Overall, the lower the BUG rating, the fewer light 
problems (and light pollution) the fixture will cause.

 y Backlight  –  this  is  the  light  that  is  spilled 
from  behind  the  fixture  into  areas  where  it  is 
unwanted. 

 y Uplight – this is the resulting light spill above 
the  top  of  the  fixture.  Uplight  contributes 
greatly  to  light  pollution  and  sky  glow  and  is 
generally not “dark-sky friendly.” 

 y Glare  –  light  glare  is  the  amount  of  front 
light in the forward zones and happens when 
the  light  is  too  strong  or  concentrated.  Glare 
is a safety issue as well as a light issue near 
adjacent properties.

Consideration should also be given to blocking light 
spill from internal light sources. This could include 
black-out blinds or shutters for transparent portions 
of a building, including sky lights (Commonwealth 
of  Australia,  2020).  This  type  of  shielding  can  be 
performed  by  fixtures  or  structures  that  are  not 
specifically  designed  for  this  purpose,  such  as 
shutters and blinds. 

However,  this  can  mean  they  do  not  always 
effectively  reduce  ecological  harm  of  ALAN,  for 
example,  in  the  Bonn  Post  Tower  Germany,  the 
shutters only attenuate but do not prevent pollution 
from emergency lighting on the floors, as they were 
designed  first  and  foremost  as  sunshades  rather 
than specifically for shielding (Korner, von Maravic 
and Haupt, 2022).

House in a forest, showing non-intentional lighting of the surrounding vegetation outside of the building, as windows without blinds 
spill light outwards. Source: https://www.pexels.com/photo/a-house-in-the-forest-12712629/

22

2.2.3.  Limitation on upward (or downward) light

Skyglow occurs when the night sky is brightened, 
often  from  the  lighting  in  cities.  It  can  impact 
natural  environments  several  kilometres,  or  tens 
of  kilometres  away  from  densely  populated  city 
centres.  For  example,  in  rural  areas  skyglow  is 
often  visible  from  adjacent  urban  environments 
or  cities  and  can  be  perceived  by  certain  species 
(Jägerbrand  and  Bouroussis,  2021;  Rodriguez  et 
al.,  2022.  Many  photo-sensitive  species,  such  as 

birds, amphibians, insects (i.e.) and bats, in areas 
without  high  levels  of  direct  ALAN,  can  still  be 
affected  by  skyglow.  However,  for  aerial  species 
it  can  be  difficult  to  distinguish  the  effects  of 
skyglow from the impacts of directly emitted light.  
A recent European study found that skyglow from 
coastal  cities  that  are  low  and  close  to  the  sea 
surface, exposes seafloor habitats to high levels of 
light pollution (Davies et al., 2020). 

Illuminated City Buildings near Water at Night, Cardiff, Wales. Source:  Duncan Richardson, https://www.pexels.com/photo/illuminated-
city-buildings-near-water-at-night-16510048/

Various  approaches  have  been  used  in  street-
lighting  planning  to  reduce  energy  consumption 
and  glare,  which  causes  discomfort  for  humans 
(see  box  1).  These  approaches  can  work  with 
specific  measures  and  define  a  limit  or  threshold 
which  should  not  be  breached.  For  example,  the 
edge  illuminance  ratio  (EIR)  represents  the  ratio 
of  the  level  of  light  inside  the  carriageway  edge, 
compared to the light outside the edge, and is used 
for roads with an adjacent footpath or a cycleway to 
ensure light levels do not negatively impact those 

on the footpath/cycleway. Whilst limiting luminous 
intensity – or the quantity of light per solid angle 
–  can  reduce  energy  consumption.  Putting  these 
limits  in  place  leads  to  a  more  precise  lighting 
design  for  roads  which,  in  turn,  helps  limit  the 
impact of light pollution on the environment. These 
are good examples of when technical management 
of  light  enables  multiple  benefits,  in  this  case 
greater  energy  efficiency,  reduced  glare  and  less 
skyglow (Jägerbrand and Bouroussis, 2021a).  

23

A more direct approach to reducing skyglow is to 
work  with  measures  of  upward  light  ratio  (ULR), 
upward  light  output  ratio  (ULOR)  or  upward  flux 
ratio  (UFR)2.  These  measures  provide  different 
representations  of  the  level  of  light  that  is 
directed upwards into the sky, and limiting them 
can  prevent  or  reduce  the  level  of  skyglow.  For 
International  Commission  on 
example,  The 
Illumination  (CIE)  recommends  maximum  ULR 
values for luminaires for different environmental 
zones  (Commission  Internationale  de  l’Eclairage, 
2017)  (see  section  2.4.2),  and  ULOR  has  been 
used in road lighting procurement in the EU with 
a  recommendation  for  0%  ULOR  for  any  lights 
(Donatello, et al., 2019). 

Light  can  also  be  reflected  upwards  from  highly 
polished, shiny or light- coloured surfaces such as 
white  painted  infrastructure,  polished  marble  or 
white sand, and this can contribute to sky glow. For 
light reflected from surfaces beneath the luminaire 
or from the surroundings then it is more suitable 
to  manage  the  UFR  for  limitation  of  skyglow  and 
light  pollution.  Measures  to  limit  this  type  of 
upward light can be quite straightforward, such as 
alternatives  to  painting  storage  tanks  with  white 
paint (Commonwealth of Australia, 2020).  

There  are  also  options  for  management  through 
the structure of the light or luminaire itself, where 
upward tilting light can be limited using appropriate 
optics,  reflectors  and  lenses  (Jägerbrand  and 
Bouroussis, 2022).

2.2.4.  Lighting control and adaptive lighting

The  scheduling  of  lighting  to  dim,  or  switch  off, 
can prevent or lessen the negative impact of ALAN 
on  species  which  are  nocturnal  or  crepuscular 
(active primarily in twilight and dawn), by creating 
dark  times.  The  use  of  a  schedule  alongside 
programmable 
is  known  as 
lighting  systems 
adaptive lighting.

The  time  at  when  lighting  should  be  dimmed  or 
switched  off,  and  for  how  long,  will  depend  on 
which species are a priority, and which part of the 
day/night  this  species  is  active  during  the  year. 
Measures of this type have been shown to reduce 
ALAN,  but  the  real  assessment  of  success  lies  in 
whether they reduce the ecological impact. 

For  example,  part-night 
lighting  has  proved 
insufficient  to  avoid  impacting  light-averse  bats 
(Azam,  et  al.,  2015),  because  their  foraging  time 
can be reduced even if lighting is dimmed during 
part of the dark time period. The time when many 
nocturnal species are most active is twilight, which 
is when human demand for light peaks. However, 
dedicated  lighting  has  proven  successful  in  some 
specific  situations,  for  example,  thousands  of 
trapped  migratory  birds  are  released  from  the 
National  9/11  Museums’  ‘tribute  in  light’,  by  the 
intermittent  switching  off  of  the  lighting  rig  (Van 
Doren, et al., 2017). 

Dimming may have an even smaller impact on light-
aversive bat species depending on the illuminance 
level (Rowse, et al., 2015), yet it may be effective 
regarding  other  less  light  sensitive  nocturnal 
species. Very few studies have combined dimming 
and  part-night  lighting  to  better  understand  the 
thresholds  of  avoidance  or  attraction  for  photo-
sensitive  species  (Jägerbrand  and  Bouroussis, 
2021b). One three-year field experiment assessed 
several  lighting  strategies  of  LEDs  on  previously 
unlit grassland ecosystems, and one of these was a 
combination of dimming by 50%, and switching off 
lights between midnight and 04.00 (Davies, et al., 
2017). Out of the four strategies this combination 
of  dimming  and  part-night  lighting  did  show  the 
most  promise  in  terms  of  fewest  taxa  affected, 
but the numbers of two common species were still 
reduced. 

However,  the  installation  of  dimmable  lighting 
may  be  considered  prudent  in  most  scenarios, 
given  that  light  intensity  is  important  for  most 
nocturnal  species,  but  threshold  data  is  largely 
absent at present. Dimmable lighting allows levels 
to  be  adjusted  lower  (or  higher)  after  installation, 
as  more  research  data  becomes  available  on  the 
ecological  impacts  of  ALAN  on  resident  species 
(Jägerbrand  and  Spoelstra,  2023).  In  a  small 

2  More detail on ratios can be found here: https://link.springer.com/chapter/10.1007/978-3-319-11466-8_16

24

study  of  two  streets  in  peri-urban  Switzerland, 
researchers  found  that  installing  street  lighting 
that dimmed when traffic was not present reduced 

light levels by 35%, overall. This regime, compared 
to full light, resulted in lower insect numbers and 
reduced bat activity (Bolliger et al., 2020).

Figure 9. Number of insects caught in a trap – total and per group – according to two different lighting regimes, 
full light versus dimmed. Overall there was a significant difference, with more than double the number of insects 
caught when full light was used versus dimmed lighting. Source: Bolliger et al., 2020 in Basic and Applied Ecology.

Consequently,  the  recommended  best-practice 
precautionary  measures 
for  photo-sensitive 
species  are  to  switch  off  lighting  or  implement 
dimming  and/or  part-night  schedules  starting  as 

early  as  possible.  Further  research  is  needed  to 
fine tune these approaches so that they work more 
effectively and without affecting other functions of 
lighting (Jägerbrand and Bouroussis, 2021b).

2.2.5.  Adaptive lighting: Smart, intelligent and nano approaches

Intelligent  lighting  has  been  proposed  as  part 
of  smart  energy  and  city  concepts.  This  consists 
of  dynamic  lighting  management  backed  up  by 
IT  tools  that  can  adjust  the  brightness  of  lamps 
independently  using  data  from  vehicles  and/or 
walkers in the region. 

visual 

to  achieve  solutions 

It  can  be  applied 
to 
multiple  problems  such  as  improving  viewing 
disturbances, 
experience, 
preventing 
lowering  energy  consumption  and 
resisting 
impacts  of  light  pollution  (Nguyen  and  Gupta, 
2022).  Central  to  this  are  sensors  that  can 
detect  reduced  light  intensity  (light-dependent 
resistors,  LDR)  and  passive  infrared  (PIR)  motion 
detectors that can detect the location  of objects.  

Modern  technology  offers  several  solutions  for 
controlling  the  switching  off  and  dimming  of 
lighting  installations.  Luminaires  can  be  dimmed 
automatically  via  scheduled  profiles  or  using 
inputs from field sensors. Motion, presence, traffic 
and  other  sensors  can  also  provide  an  additional 
level  of  smartness  to  help  adapt  lighting  levels 
according to variable conditions. In LED luminaires, 
drivers  can  also  be  pre-programmed  to  follow  a 
specific profile throughout the year without adding 
significant costs to the equipment itself. 

Manufacturers  also  now  produce  solutions  that 
allow  lighting  to  be  linked  to  customer  demands 
through the Internet of Things (IoT), which uses the 
Internet to link physical objects with gadgets, such 
as household appliances and industrial machinery. 
When  equipped  with  sensors  and  communication 

25

networks  these  gadgets  can  provide  important 
data  for 
individual  services  and  monitoring. 
Research has shown the benefits of IoT systems to 
reduce light pollution through a real-time pollution 
surveillance  network  (Nguyen  and  Gupta,  2022). 

Looking  to  the  future,  relevant  innovations  and 
technologies that are currently in development, for 
example  autonomous  vehicles,  could  incorporate 
night-time  lighting  into  their  design  at  the  early 
stages (see box 4).

In the USA, approximately 30% of outdoor lighting is considered to be 
“wasted,” estimated to cost upwards of 7 billion US dollars per year. 
Furthermore, eliminating this excess lighting could have the same 
reduction in CO2 emissions as removing ~ 9.5 million cars from the road.

Source: Gallaway, et al., 2010

An estimate of the excess and wasted night-time lighting in the European 
Union puts the costs at over 5 billion euros per year 

Source: Morgan-Taylor, 2014.

26

Box 4: Autonomous vehicles and light pollution (Stone, Santoni de Sio 
and Vermaas, 2020)

Autonomous vehicles are currently still a technology 
in  development.  The  design  of  both  the  vehicles 
and  the  surrounding  infrastructure  are  open-
ended.  Researchers  have  proposed  that  night-
time lighting should be a priority consideration for 
autonomous  vehicles  during  their  development 
phase,  and  that  if  designed  correctly  they  could 
enable  a  reduction  in  light  pollution  and  a  better 
balance of lighting and darkness. For example, the 
AI  system  of  self-driving  cars  could  be  designed 
to  incorporate  controls  to  quickly  and  efficiently 
adjust the amount of light needed from headlights, 
altering  it  dynamically  depending  on  the  level  of 
light  needed.  If  all  cars  were  able  to  apply  this 
technology, it could result in significantly reduced 
light emissions (Eliot, 2022).

taking  a  design 

for  values  approach, 
By 
considerations  around  dark  skies  and  ALAN 
reduction can be incorporated into this technology 
during its development phase. Lighting strategies 
for  vehicles  could  be  replaced  with  alternative 
technologies  that  bring  some  darkness  back  into 
landscapes.  Alongside  the  possibility  of  extra 
smart  lighting  within  a  new  AI  technology,  there 
are multiple ways in which driverless cars can be 
implemented that could aim to minimise ALAN. For 
example,  two  hypothetical  scenarios  explored  by 
Stone,  et  al.  (2020)  are  one  in  which  automated 
cars drop their passengers off and then find parking 
in  unlit  lots,  and  another  in  which  highways  no 
longer require lighting except for emergencies and 
at exit ramps. Both of these scenarios could reduce 
ALAN  but  would  require  behavioural  change  and 
development  of  trust  in  these  new  technologies 
and their approaches (Brandon, 2019).

The  use  of  IoT  and  smart  systems  enables 
production  of  large  monitoring  datasets.  Working 
with  these  AI  techniques  have  broad  potential  in 
the lighting industry to improve the illumination in 
the buildings, reduce energy usage and give light 
the  same  quality  as  sunshine  through  machine 
learning approaches.  

Nanomaterials are also opening up new possibilities. 
At  the  nanoscale,  materials  can  become  better 
conductors for heat, or reflect light, whilst others 
change  colour  or  become  stronger.  Working  at  a 

nanoscale, researchers have used flexible carbon-
based  sheets  to  improve  the  luminosity  and 
efficacy of LEDs, developing new forms of lighting 
known  as  organic  LEDs.  Semiconductors  made 
from nano-material phosphorus are being used to 
make  LEDs  that  convert  blue  light  into  a  warmer 
shade of white – this is done by producing a false 
sensation  of  brightness  from  the  use  of  green 
light, creating LEDs that are not so dominated by 
blue wavelengths (Nguyen and Gupta, 2022)

2.3.  Thresholds of artificial light to eliminate environmental harm 

In  order  to  mitigate  the  impacts  of  ALAN  on  the 
environment  for  all  types  of  locations  or  species, 
it  is  useful  to  establish  a  threshold  on  a  type  of 
light measurement, that reduces or eliminates any 
environmental harm. Once this threshold has been 
identified, often based on research insight into the 
level of ‘toxicity’ from light that can be tolerated, 
then  designers  and  decision-makers  should 
consider  this  as  an  upper  limit  on  the  amount  of 
artificial light. Thresholds can then be used to set 
up  zones  where  these  limits  cannot  be  breached 
(Commonwealth of Australia, 2020).

Thresholds  are  used  to  manage  all  forms  of 
pollution,  and  most  well-known  pollutants  have 
been  studied  extensively  for  many  decades  to 
establish their toxicity, and dose-effect responses 
on organisms, humans and the environment. 

Such  evidence-based  knowledge  is  crucial  to 
establish threshold values, but in lighting research 
there is presently a lack of high-quality, controlled 
evidence-based research on dose-effect responses 
(Jägerbrand,  2022;  Jägerbrand  and  Spoelstra 
2023).  There  are  a  few  controlled  studies  on 

27

individual species that incorporate more than one 
light level in their experiments, for example a recent 
study on the greater wax moth (Galleria mellonella 
L.) to 14 different light intensities (Jägerbrand, A. 
et al., 2023). 

Collaborations  between  researchers  of  ALAN’s 
environmental impacts and lighting designers should 
be  fostered  to  identify  relevant  issues  that  guide 
future research. Supporting evidence-based lighting 
design  approaches  and  technological  solutions, 
including  light  sources,  lighting  controls,  luminaire 
design  and  appropriate  measurement  methods  will 
enable the identification of thresholds and application 
of  appropriate  mitigation  to  benefit  environmental 
health (Zielinska-Dabkowska et al., 2023). 

Thresholds  differ  according  to  the  species,  the 
variable that defines the threshold and the function 
or behaviour that is disrupted so their identification 
may not always be practical. For example, a study 
on the impact of light pollution from the Bonn post 
tower  showed  that  even  faint,  but  exposed  light 
sources,  attract  and  disorientate  migratory  birds, 
concluding  that  it  was  not  possible  to  define  an 
intensity level that was low enough not to produce 
this effect (Korner, von Maravic and Haupt, 2022). 

As migration is not a constant activity, this finding 
suggests that the best approach to reduce negative 
impacts  on  migratory  birds  may  be  to  switch  off 
lights at those times when birds are migrating. A 
novel approach to this is to forecast or predict the 
numbers of migratory birds in a specific city from 
a range of ecological variables, and on those days 
when the levels are high to implement ‘Lights out 
Action Alerts’. 

The  Colorado  State  University  AeroEco  Lab  has 
created alert maps for the US states and cities of 
relative migration intensity. These maps have four 
levels: no alert, low, medium, and high. A high alert 
is a night that will see a large amount of migration 
activity and these events account for only 10% of 
the nights in a season but account for 51% of the 
total seasonal movement3. A similar approach was 
taken  by  ‘World  Migratory  Bird  Day  2022’4  which 
adopted the theme of “Dim the Lights for Birds at 
Night” to raise awareness of this as an approach 

in this area. 

The  debate  around  thresholds  and  measures 
becomes  more  complex  when  considered  at  the 
regional  or  global  scale  using  larger  datasets 
and modelling techniques. European research has 
modelled changes of European light emissions using 
satellite data (Widmer et al., 2022) by considering 
two thresholds of radiance: 2 nW/cm2sr, at which at 
least a low ecological impact can be expected, and 
of 0.5 nW/cm2/sr, which is the lowest light level of 
light emissions that can be measured by satellite 
monitoring. However, 0.5 nW/cm2/sr is the natural 
luminance of the night sky without artificial light, 
and  not  the  generally  accepted  threshold  for  a 
truly  dark  sky.  However,  this  satellite  data  only 
models  light  emitted  upwards,  not  light  emitted 
downwards,  effecting  species  below  streetlights, 
for example.

Decreasing  light  intensity  is  essential  to  prevent 
negative impacts of ALAN on highly photosensitive 
nocturnal  species  which  are  sensitive  even  to 
low  light  levels.  Due  to  the  problematic  nature 
of  identifying  threshold  light  intensity  levels,  it 
may  be  prudent  to  keep  light  levels  below  lower 
moonlight  levels  whenever  possible  ranging  from 
0.05 to 0.1lux  (Jägerbrand and Spoelstra 2023).

A different, but conceptually similar approach to light 
thresholds, is to consider optimal levels for different 
functions  for  humans  (e.g.  to  enable  visibility  for 
safety, enhancing aesthetics of cultural sites) with 
a limit placed on the maximum use above this level. 
The  main  aim  of  these  is  to  not  use  more  light 
than necessary to achieve the function required for 
human use, and so avoid ecological impacts as far 
as possible. In the case of the function of improving 
visibility,  these  levels  are  based  on  human  visual 
capabilities  and  can  vary  for  different  groups,  for 
example  older  persons  (>65  years)  will  have  more 
difficulty detecting obstacles at very low illuminance 
values  (0.2lux).  There  are  other  functions  to  be 
considered, such as improving energy efficiency, so 
that the use of illumination levels for functions can 
enable the ALAN management to be more tailored 
to the needs of the community. 

The Colorado State University AeroEco Lab has created alert maps: https://aeroecolab.com/uslights

3 
4  World migratory bird day 2023, May 13th and October 14th: Water #WMBD2023 | World Migratory Bird Day

28

Box 5: Units of light – common measurement terms – for further 
standardised technical details refer to the CIE website5 

(Source: https://www.lumitex.com/blog/light-
measurement#1 and e-ILV | CIE) 

Illuminance  is  the  amount  of  luminous  flux  per 
unit area (or luminous emittance) and is measured 
in  lux  where  one  lux  is  equal  to  one  lumen  per 
square meter – lm per m2.

Luminous intensity is the quantity of light that 
is  emitted  in  unit  time  in  a  definitive  direction. 
It  is  measured  in  Candela  (cd)  which  is  unit  of 
luminous  intensity  per  unit  time  per  unit  solid 
angle where 1 lumen = 1 candela x steradian (the 
SI unit of solid angle).

Luminous Flux is the amount of energy a light emits 
over time, which is weighted to the spectral sensitivity 
of human vision, measured in lumens (lm).

Luminance is the intensity of light from a surface 
per unit area in a given direction measured as cd 
per m2. 

Radiance  is  the  radiant  flux  emitted,  reflected, 
transmitted or received by a given surface, per unit 
solid angle per unit projected area and is measured 
in watts per square metre per steradian W/m2/sr. 
Radiance is useful because it indicates how much 
of  the  power  emitted,  reflected,  transmitted  or 
received by a surface when looking at that surface 
from a specified angle of view.

5 

CIE ILV, offers standardised (technical) definitions for light and lighting for lighting professionals and researchers: https://cie.
co.at/e-ilv

 
There are numerous ways to measure and assess 
light  dependent  on  what  you  are  studying  (see 
box 5). The regulations of different countries vary 
in  how  they  plan  and  measure  light,  the  type  of 
lighting  installations  for  which  limits  are  defined, 
or  the  allowed  area  for  which  light  needs  to  be 
controlled/managed. 

For  example,  France  has  included  strict  metrics 
in  its  policy  regulating  outdoor  lighting,  where 
light  emissions  are  measured  in  illuminance,  and 
three  thresholds  have  been  identified  depending 
on the level of urbanity. Whereas in Korea light is 
measured in luminance, and the areas depend on 

29

the number of photo-sensitive species that inhabit 
the  area.  Croatia  uses  a  similar  zone  system  to 
Korea, and combines it with illuminance similar to 
France (Widmer  et al., 2022).  

have 

countries 

Some 
implemented 
recommendations  on  the  colour,  or  spectral 
properties of the light sources (referred to as CCT, 
or colour corrected temperature), e.g. France, below 
or  equal  to  3000K  for  exterior  lighting,  below 
or  equal  2400K  for  natural  areas  and  sites  for 
astronomical  observations.  The  recommendation 
for  a  lower  CCT  is  based  on  the  assumption  that 
this correlates with a reduced amount of blue light.

Comparison of correlated colour temperature (CCT) of five lamps (indoor compact fluorescent light bulbs). From left (warmer yellow) to 
right (cooler blue): 2700K, 3500K, 4100K, 5500K, 6500KCFL. The warmer yellow lower CCT light, is suggested for exterior lighting due 
to the lower amount of blue light – known to be harmful to many nocturnal species. Source: User: Splarka, Public domain, via Wikimedia 
Commons, https://commons.wikimedia.org/wiki/File:Color_temperature_comparison_of_5_CFLs.jpg

30

2.3.1.  Lighting measurements and assessment 

Appropriate  instrumentation  and  methods  are 
needed to make the initial assessment of where ALAN 
needs to be managed, to establish the thresholds 
to  manage  it  and  to  monitor  the  effectiveness 
of  these  initiatives.  These  measurements  do  not 
work in isolation with developments requiring input 
from lighting designers and contextual information 
regarding the local habitat and any light-sensitive 
species present from ecological surveys. 

When new outdoor lighting installations are being 
established, light levels should be measured during 
the  construction,  operation  and  maintenance 
periods.  This  enables  designers  to  adjust  the 
lighting  design,  to  meet  design  requirements 
whilst  also  identifying  any  obtrusive  lights  for 
removal  or  mitigation.  Monitoring  the  variation 
of  sky  glow  in  the  long  term  is  also  important, 
to  assess  the  increase  or  the  restoration  of 
the  brightness  level  towards  the  set  target 
(Jägerbrand and Bouroussis, 2021a).

Currently  there  are  many  possible  ways  to 
measure light and its impact on the environment 
and  there  is  no  universally  accepted  metric  or 
approach to measurement. Due to the variety of 
species that may be affected by artificial light the 
task  of  measurement  is  challenging  and  needs 
to consider their light exposure, location, field of 
view  and  spectral  sensitivity.  Measurements  in 
the  field  are  typically  performed  at  night  or  at 
twilight,  under  various  weather  conditions,  and 
can be done at a particular time, multiple sets of 
times or long-term monitoring. 

the  ground 

Measuring  ecological  light  pollution  at  smaller 
scales  on 
requires  different 
measurement  techniques,  depending  on  the  light 
source  and  the  species  or  ecosystem  of  concern. 
The measurement device chosen needs to account 
for the specific animal’s eyes, and the sensitivity of 
the measurement device. Light traps can be used 
to observe ground-based wildlife, whereas drones 
might be used to simulate the positioning of flying 
animals,  to  gain  for  example,  a  migratory  bird’s 
eye  perspective  of  ALAN  (Kocifaj,  Wallner  and 
Barentine, 2023).  

The dominant quality of light that is measured is 
horizontal  illuminance.  This  means  that  the  most 
used instrument is a hand-held illuminance meter 
or  luxmeter  that  measures  the  amount  of  light 
that  falls  on  an  area.  These  meters  are  designed 
to  match  the  human’s  eye  spectral  sensitivity, 
which limits their applicability for species with very 
different sensitivities (Jägerbrand and Bouroussis, 
2021b).  Although  it  is  important  to  strive  for 
more  standardised  light  measurement  to  better 
understand the impacts of ALAN, it must also be 
remembered that due to complexity of ecosystems 
and  the  environment,  ecological  impacts  cannot 
be  anticipated  or  assessed  by  the  measurement 
of  light  alone.  The  positioning  of  light,  how  it 
sits  within  the  immediate  environment  and  other 
indirect  effects  it  may  have  such  as  attracting 
predators, must be considered.  

Guidelines 
reporting 
for  documenting  and 
light  pollution  of  ecological  and  environmental 
relevance  encompass  a  comprehensive  approach 
that  involves  assessing  both  the  ambient  light 
pollution in the environment and the specific light 
exposure experienced by the organism that is being 
studied. To document light pollution accurately, it is 
essential to measure illuminance and/or luminance 
levels  at  multiple  locations  in  various  directions, 
while  also  considering  spectral  distribution. 
Additionally,  providing  a  detailed  description  of 
light in three dimensions enhances the repeatability 
of  the  assessment.  When  evaluating  the  light 
exposure of species, it becomes crucial to measure 
light where individual organisms perceive it and in 
relevant directions. Furthermore, it is advisable to 
express these measurements in units of biological 
significance,  such  as  radiance,  to  ensure  that  the 
assessment aligns with the biological relevance for 
living organisms. 

Box 6: STARS4ALL project (Source: https://stars4all.eu/)

31

The STARS4ALL Foundation Is a hub for the results 
of  this  project,  sharing  data  among  the  TESS 
photometer network and providing open data form 
this to the public.

European  Union/European 

The 
Commission 
supported  'STARS4ALL'  –  a  project  to  encourage 
investigations  and  collaborative  infrastructure  in 
Europe  for  fostering  dark  skies  –as  part  of  the 
Horizon  2020  Programme  between  2016  and 
2018.  Among  the  breakthroughs  was  the  Dark 
Sky  Meter  app,  that  monitors  sky  luminance  and 
exchanges data with researchers all over the world. 
Another  technology  developed  was  the  TESS-W 
photometer, capable of measuring and providing a 
continual assessment of the night sky illumination 
– for light pollution investigations. 

Tess W photometer, a device which can be used to measure night sky illumination. Source: https://tess.stars4all.eu/faqs/.  
Photo of the left by Lucía García and photo of the right by Alexis Mancilla

Remote  sensing  is  also  used,  mainly  wideband 
radiance  and  red/green/blue  maps  from  the 
International Space Station. This provides valuable 
data  on  spatial  distribution  of  illuminated  areas 
and  an  estimation  of  illuminance  levels,  but  the 
information  concerns  only  direct  or  reflected 
upward radiance, without an indication of the 3-D 
propagation of light. 

Skyglow measurement tends to use two dominant 
techniques  –  the  Sky  Quality  Meter  or  the 
commercial RGB imaging cameras, but there is no 
standardisation in their units. 

One  of  the  research  priorities  in  this  field  is  to 
establish  a  more  standardised  way  to  describe 
ALAN,  define  thresholds  and  monitor  measures 
to reduce its negative impact (see Chapter 3 for 
more exploration). 

32

2.4.  Management interventions and best practice for mitigating ALAN 
impacts on the environment 

Alongside technical solutions around light, and light 
installations,  there  are  a  range  of  management 
interventions  that  work  at  a  systemic  level  to 
address the impact of ALAN. These implement the 
technical  approaches  alone,  or  in  combination,  in 
a way that best addresses the specific challenges 
posed  by  ALAN  in  a  region,  or  for  a  species  or 
ecosystem. These can include integrated measures, 
to  protect 
lighting  masterplans 
outlined 

in 

against  ALAN  in  local  planning  aiding  efficient 
infrastructure design. ALAN focussed management 
interventions can also seek to define geographical 
lighting zones, or identify species and ecosystems 
that  require  specific  protection.  These  emerging 
mitigation interventions often dovetail into existing 
environmental  management  interventions,  aimed 
at  climate  change,  biodiversity  degradation  and 
carbon reduction. 

2.4.1.  Lighting masterplan and efficient design 

A  lighting  masterplan  is  a  strategic  document 
that  acts  as  a  framework  for  subsequent  design 
decisions on public lighting, particularly in cities. It 
serves a number of purposes in terms of defining 
the  aesthetic  and  functional  lighting  criteria,  and 
increasing the efficiency and quality of city lighting, 
with the ultimate goal of securing a comfortable, 
and well-structured lit environment. 

efficient  lighting  design  techniques,  including  the 
appropriate  equipment,  optics,  lenses,  and  other 
relevant  technologies.  The  masterplan  should 
also  work  at  the  macro  level,  defining  those 
areas that need more protection from ALAN with 
environmental  lighting  zones  (see  section  2.4.2) 
and  areas  that  need  more  visibility  for  safety 
(Zielinska-Dabkowska, 2016).,

The  lighting  masterplan  should  be  integrated 
into  urban  development  sustainability  studies, 
and  include  the  minimisation  of  the  potential 
negative impacts on the environment (Jägerbrand 
and  Bouroussis,  2021a).  This  masterplan  should 
include  details  of  what  is  needed  to  implement 

The aim of the masterplan is to serve the lighting 
needs  in  an  optimised  way,  by  creating  a  holistic 
picture  of  the  area  that  details  the  technical 
solutions  at  the  local  level  (Jägerbrand  and 
Bouroussis, 2021a).

Box 7: Road lighting planning and decision-making for government roads 
in Sweden

33

The  Swedish  Transport  Administration  has 
established a decision-making process to assess 
the  need  for  comprehensive  environmental 
analysis,  and 
light 
pollution mitigation measures along roads under 
its jurisdiction.  

implementation  of 

the 

Generally,  road  lighting  or  decorative  lighting 
should be avoided outside urban areas, except for 
road lighting in complex situations. 

Some  fundamental  requirements,  including  those 
to be introduced in 2024, encompass: 

 y Luminaires must have flat glass;

 y The  maximum  correlated  colour  temperature 
should  not  exceed  3000K  (i.e.  yellow,  warm 
white light);

 y Criteria for reducing light pollution via upward 

light ratio (ULR);

 y Requirements for luminaire efficiency (lm/W);

 y Limits  on  over-illuminated  roads,  allowing  a 
maximum of 20% excess light above minimum 
requirements;

 y Standard  night-time  light  reductions  for  all 
luminaires, operating at 60% and 40% of full 
effect during night-time; 

 y Mandates  for  presence-controlled  pedestrian 

and bicycle paths, when applicable;

 y Mandatory  deactivation  of  all  decorative 

lighting at 10pm;

 y No lighting permitted at wildlife passages, with 
exceptions made for multi-use overpasses and 
underpasses.

in  all  environments, 

Rather than universally applying the precautionary 
principle 
the  Swedish 
Transport  Administration  has  devised  a  lighting 
planning  tool.  When  deciding  to  construct  a  new 
road  or  renovating  an  existing  one,  designers  are 
required to employ this tool. The tool incorporates 
Geographic 
(GIS)  data, 
Information  System 
highlighting  areas  of  ecological  significance.  The 
GIS  data  is  sourced  from  various  databases,  and 
specific  criteria  are  established  to  determine  the 
ecological importance of an area. 

In cases where planned lighting intersects with a 
designated  nature  value  area  (within  a  distance 
of  ≤  50  m  from  the  road*),  this  serves  as  an 
indicator that standard lighting should potentially 
be  avoided.    This  situation  necessitates  a  more 
comprehensive  analysis,  to  be  conducted  by  an 
ecologically competent individual from the Swedish 
Transport Administration. 

Following the analysis, a decision can be reached 
to  determine  whether  the  lighting  has  an  impact 
on the local fauna. If such an impact is identified, 
additional measures and actions are required.  

Additional actions to be taken in the presence of a 
nature value area:

 y implementing  night 

time  curfews  during 

specific times and seasons as needed;

 y  opting  for  correlated  colour  temperatures 

below 3000K;

 y  minimizing  spill  light  and  employing  shielding 

techniques; 

 y installing  physical  barrier  such  as  planks  or 

lightproof fabric;

 y exploring  measures  to  reduce  speed  or  other 
solutions  to  enhance  traffic  safety,  thereby 
reducing the reliance on road lighting.

34

Below is an image from the lighting planning tool displaying a planned road intersecting a nature value 
area, specifically a swamp forest (Figure 10). 

Figure 10. A picture depicting the light planning tool showing a planned road intersecting a nature value area. 
Green lines enclosed in grey represent roads with a requirement for lighting. The blue dashed area represents 
swamp  forest,  designated  as  a  nature  value  area  requiring  special  consideration  in  road  lighting  planning.  
© Petter Hafdell, using  GIS software

2.4.2.  Environmental lighting zones

The  use  of  specified  zones  within  which  there  is 
a  maximum  admissible  level  of  a  pollutant,  is  a 
well-recognised  method  to  limit  environmental 
harm.  This  has  been  adopted  within  the  field  of 
light pollution where types of zones are described 
according  to  the  desired  level  of  lighting,  and 
then  caps  on  light  emissions  are  determined  for 
these zone types. The aim of these environmental 
lighting zones is to help stop further deterioration 
of areas that need protection. 

Not only can zones enable protection of specific areas, 
but it can also classify larger land areas into zones of 
different character. This macroscale overview can help 
inform which areas should be prioritised in strategic work 
with natural environments, or to gain insight into which 
natural environments should be protected from future 

light pollution (Jägerbrand and Bouroussis, 2021b).

There are several benefits to dividing an area into 
zones. Firstly, it is easier to work at the landscape 
level when incorporating nature conservation into 
a planning process. Also, the use of environmental 
lighting  zones  in  the  urban  planning  process,  will 
quickly identify lighting needs for a range of areas 
and functions (Jägerbrand and Bouroussis, 2021b).

A  number  of  lighting  zone  classification  schemes 
have  been  proposed,  with  the  most  well-known 
including:    the  European  based  CIE  (Commission 
Internationale  de  l’Eclairage,  2017),  the  North 
American based IESNA-IDA (International Dark-Sky 
Association  and  Illuminating  Engineering  Society, 
2011), and the RASC dark sky protection program 
(Royal Astronomical Society of Canada, 2018).

35

The  CIE  environmental  lighting  zones  are  based 
on the ambient brightness of the environment and 
are divided into zones from E0 to E4, ranging from 
intrinsically  dark  to  high  district  brightness  (see 

table 3). The IESNA-IDA Model Lighting Ordinance 
uses lighting zones (LZ-0 to LZ-4) and recommends 
lighting design and use within the lighting zones. 

Table  3:  Environmental  lighting  zones  and  examples  of  areas,  please  note  sky  quality  meter  (SQM)  depicts 
luminance – or the light given off by a surface – in magnitudes per square arc second. Source: adapted from 
Jägerbrand and Bouroussis, 2021b; lighting zones source:CIE 150:2017; SQM values souce: Institute of Lighting 
Professionals, 2021.

Zone

Lighting Environment

Surrounding area

Examples

E0

E1

E2

E3

Intrinsically Dark  
(SQM 20.5+)

Protected

Dark 
(SQM 20-20.5)

Natural

Low district brightness 
(SQM ~15-20)

Rural

Medium district 
brightness

Suburban

E4

High district brightness

Urban

UNESCO Starlight reserves, 
IDA Dark sky places. 
Astronomical observable 
dark skies.

Relatively uninhabited rural 
areas. Areas of outstanding 
natural beauty. IDA buffer 
zones.

Sparsely inhabited rural 
areas, villages, or relatively 
dark outer suburban areas.

Well inhabited rural and 
urban settlements, small 
town centres or urban 
locations.

City, and town centres with 
high levels of night-time 
activities.

In the case of skyglow, which impacts large areas, 
and can extend far from the source itself, limitation 
measures can extend beyond the country or regional 
limits.  An  intergovernmental  understanding  and 
common  actions  might  be  useful  in  long-term 
strategies  for  skyglow  limitation,  (Institution  of 
Lighting Professionals, 2021). Currently to prevent 
skyglow,  the  Institution  of  Lighting  Professionals 
(ILP)  recommends  maximum  values  for  levels  of 
light directed upwards into the sky (ULR or ULOR) 
for  the  different  CIE  zones,  and  in  the  case  of 
ULOR  it  also  categorises  it  according  to  the  type 
of installation. 

Based on the recommendations of the ILP, an area 
to be lit lying close to the boundary of two zones 
should  be  subjected  to  the  limitation  standard 
applicable to the most rigorous zone (Institution of 
Lighting Professionals, 2021).

Zoning  approaches  to  light  pollution  can  also  be 
embedded in existing networks of projected areas. 
For  example,  the  EU  already  has  a  network  of 
protected areas in Natura 2000, and the Habitats 
Directive  requires  Member  States  to  take  the 
necessary measures to avoid significant disturbance 
of  protected  species  in  these  sites,  which,  where 
relevant, is applicable to light pollution. 

36

In  the  context  of  environmental  management 
in  protected  natural  areas,  employing  more 
than  five  environmental 
lighting  zones  can 
prove  advantageous.  This  approach  facilitates 
the  identification  of  areas  characterised  by  the 

highest  light  levels.  Using  too  few  zones  may 
result  in  a  situation  where  numerous  areas  fall 
within each of the three pertinent environmental 
lighting  zones  (E0  -  E2)  (Jägerbrand,  Brutemark, 
and Andersson, 2023). 

2.4.3.  Definition of ALAN-free areas and ecosystems

ALAN-free  areas  should  be  defined  to  enable 
the  implementation  of  the  strictest  limits  on  the 
spectrum, shielding and total amount of illumination, 
even  inside  cities.  Examples  of  areas  that  should 
be ALAN-free are environmentally sensitive areas 
or  ecosystems,  intrinsically  dark  areas,  nature 
reserves  and  habitats  with  endangered  species 
in need of protection (Jägerbrand and Bouroussis, 
2021a).  For  example,  the  Czech  Republic  has 
identified  four  regions  with  pristine  night  skies  - 
Bystřická,  Manětínská,  Jizerská  and  Beskydská  - 
that need to be protected (Widmer et al., 2022).

The  goal  of  ALAN-free  areas  is  to  retain  or 
restore the night sky luminance, and the ambient 
lighting  to  natural  levels.  Even  if  this  might  not 
be possible everywhere, it is important to protect 
the  environment  from  further  deterioration,  and 
to  implement  adaptation  measures  to  stop  the 
direct impacts of ALAN. The zoning system defined 
by  the  CIE  (2017)  for  the  zones  E0  and  E1  can 
initially  be  adopted  for  these  areas.  Protected 
or  sensitive  areas  may  require  extra  protection, 
including  connectiveness  of  dark  zones  between 
areas, and buffer zones around the protected area, 
with  restrictions  on  outdoor  lighting,  if  there  is  a 
risk  of  ecological  impact  from  light  (Jägerbrand 
and  Bouroussis,  2021a;  Institution  of  Lighting 
Professionals, 2021). 

Aurora Borealis in Sutherland, UK. The dark skies of North West Scotland enable the aurora borealis to be clearly seen.  
Source: Andrew Tryon, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons

37

Box 8: The International Dark-Sky Places (IDSP) program.

This  was  established  by  the  IDA  in  2001  to 
recognize  and  protect  areas  with  extraordinary 
night-time features for future generations, as well 
as  encourage  awareness  of  the  issues  involved. 
It  encourages  cities,  parks,  and  conserved  places 
all across the world to preserve and protect dark 
locations  by  promoting  smart  lighting  policy, 
and  public  awareness.  It  does  not  specifically 
aim  to  protect  species  from  the  impact  of  ALAN. 
Candidates must go through a rigorous application 
includes  demonstrating  strong 
process 

that 

community  support  for  dark  sky  protection.  The 
program  offers  five  certification  categories. 
As of January 2023, there are 201 certified Dark 
Sky Places in the world. These include 115 Parks, 
38  Communities,  20  Reserves,  16  Sanctuaries,  6 
Urban  Night  Sky  Places,  and  6  Dark  Sky  Friendly 
Developments of Distinction. 

https://www.darksky.org/our-work/conservation/
idsp/

Box 9: Lighting Protocol for Dark Sky Parks

International  guidance  on  artificial  light  at  night 
mitigation measures, for within a designated ’Dark 
Sky Park’, have been developed in association with 
the  International  Dark-Sky  Association.  Based  on 
the  guidance,  the  measures  apply  to  all  property 
and structures within a dark sky preserve and are 
designed  to  limit  glare  and  adverse  ecological 
impacts  of  artificial  lighting  throughout  dark  sky 
parks  (DSP)  –  providing  technical  specifications 
for  acceptable  illumination  levels  for  navigating 
safely within the park. Suggestions are also made 
regarding  lighting  policies  that  could  be  applied 
to  urban  areas  beyond  the  park  boundaries,  to 
protect  the  DSP  from  deterioration  from  nearby 
light pollution (RASC and Dick, 2020). 

 y Signage  should  not  use  active  lighting. 
Instead,  retro  reflective  materials  should  be 
used with signs mounted less than 1m off the 
ground so people using flashlights after dark 
can see them.

 y Only 

full 

(FCO) 

cut-off 

fixtures 
should  be  used.  Existing 
lights  should 
be  shielded  or  replaced  with  FCO  fixtures 
to  prevent  light  from  shining  beyond  the 
immediate  area  that  requires  illumination. 

 y Illumination  level  produced  by  fixtures 
should  be  as  low  as  is  practical.  For 
vehicles this is suggested as 3 lux, or 0.3fc for 
large  parking  areas  with  high  traffic  density, 
where speed limits are in effect. Whereas with 
pedestrians only 1 lux or 0.1fc is needed. Lower 
light  wattages  can  be  used  as  it  is  assumed 
that pedestrians will have flashlights and cars 
will  have  headlights.  These  lights  serve  as 
markers, phosphorescent markers can also be 
used.

 y Structures  and  barriers  (such  as  trees 
or  shrubs)  should  be  used  to  confine 
illumination to the immediate area.

 y All  light  sources  should  be  turned  off 
within 2-hours of sunset, automatic timers 
should be used to avoid the need for staff to 
turn off lights.

 y Indoor lighting should be prevented from 
shining  through  exterior  windows  by 
using curtains within 30 minutes of sunset – 
if indoor lighting is still necessary.

 y All light fixtures should emit a minimum 
of  UV  and  blue  light,  with  white  lights 
not used at all. Sodium lamps, incandescent 
lamps and amber LEDs may be used, but UV 
lights should not be used at all as they attract 
flying insects.

 
 
 
38

2.4.4.  Dark infrastructure 

Green  and  blue 
infrastructure  policies  have 
been  developed  globally  based  on  the  concept 
of  ecological  networks,  recognising  that  within 
fragmented 
landscapes  a  set  of  suitable 
interconnected  habitats  need  to  be  preserved  to 
support  biodiversity,  and  deliver  a  wide  range  of 
ecosystem services. 

Research  has  shown  that  ALAN  is  present  in  all 
of  the  major  habitat  categories,  which  includes 
terrestrial,  aerial,  aquatic,  wetlands  and  marine 
areas  (Sordello  et  al.,  2022),  but  currently  nature 
conservation  policies  around  blue  and  green 
infrastructure  have  limited  consideration  of  the 
adverse effects of ALAN. A good example of where 
it has been considered is the resolution adopted by 
the  International  Convention  on  the  Conservation 
of Migratory Species of Wild Animals (CMS), which 
recognises  that  ALAN  is  an  emerging  issue  for 
wildlife.  Recently  the  CMS  launched  a  new  online 
guide  to  help  cities  around  the  world  reduce  the 
impacts of light pollution on wildlife (Nunny, 2021). 
The  guide  offers  facts,  case  studies,  information 
resources, and a checklist for cities to reduce the 
harmful effects of artificial lighting on wild animals 
(Nunny, 2021; Cities with nature, 2023)6.

Researchers  and  planners  have  proposed  that 
darkness quality should be integrated within blue 
and  green  infrastructure  to  implement  a  dark 
infrastructure.  The  result  would  be  an  ecological 
network – formed by cores connected by corridors 
–  in  which  darkness  is  an  additional  quality  that 
needs to be managed, with the goal of preserving 
and restoring an ecological network with a level of 
darkness  that  is  as  natural  as  possible,  and  that 
enables maintenance of biodiversity.

To  use  this  framework  dark  infrastructure  must 
be  identified,  preserved  and  restored  at  different 
landscape  levels,  to  enable  ecological  continuities 
where the night and its rhythms remain as natural 
as possible. Researchers have proposed a four-step 
process for this which must be implemented across 
different  administrative  and  ecological 
levels, 
bringing together top down planning schemes and 
bottom up insights from local inhabitants (Sordello  
et al., 2022). The four steps are outlined in figure 10.

Figure  11:  Four  steps  to  implement  dark  infrastructure 
(Sordello et al., 2022). Source: © 2022 Romain Sordello, 
Samuel Busson, Jérémie H. Cornuau, Philippe Deverchère, 
Baptiste  Faure,  Adrien  Guetté,  Franz  Hölker,  Christian 
Kerbiriou,  Thierry  Lengagne,  Isabelle  Le  Viol,  Travis 
Longcore, Pascal Moeschler, Jessica Ranzoni, Nicolas Ray, 
Yorick Reyjol et al. Published with license by Elsevier B.V. 
Available via CC BY 4.0

 y The  first  step  of  mapping  involves  depicting 
the  spatial  distribution  of  darkness  quality.  It 
can use a range of indicators including satellite 
images,  field  data,  light  measurements  and 
aerial photography that gives a bird’s eye view 
of  the  landscape.  The  pros  and  cons  of  each 
data  source  depend  on  the  scale:  national, 
regional, municipal, neighbourhood. 

 y The  second  step  of  identification  signposts 
the  use  of  thresholds  to  limit  ALAN  and 
enable  dark  infrastructure.  Once  the  cut-off 
threshold  is  chosen  there  are  two  options  for 
implementation:  either  accounting  for  ALAN 
in  existing  green  or  blue  infrastructure,  or 
integrating ALAN in the design of new green or 
blue  infrastructure  (see  box  10  for  examples). 

6 

‘Curb light pollution in your city’ available at: https://citieswithnature.org/curb-light-pollution-in-your-city/

 y The 

includes 

third  step  of  preservation  and 
restoration 
technical  and 
the 
management  approaches  that  have  been 
covered  in  this  brief,  and  highlights  that  light 
pollution  must  be  reduced  without  losing 
comfort  and  function  for  human  activities 
'sobriety’7.  
–  a  concept 

referred 

to  as 

39

 y Finally, in its fourth step the framework outlines 
the  importance  of  assessing  effectiveness 
of  dark  infrastructure,  and  monitoring  this 
to provide feedback into mapping of darkness 
quality. Monitoring should include indicators of 
light pollution, and those related to biodiversity, 
such as species richness and abundance – as 
well as measures of functional and structural 
connectivity (see section 2.4.6). 

Box 10: Examples of dark infrastructure implemented in Europe  
(Sordello et al., 2022)

After  a  cut-off  threshold  is  chosen  for  what 
constitutes  a  dark  infrastructure,  Sordello  et  al. 
(2022) suggest two approaches to implement dark 
infrastructure. 

 y Taking an existing green/blue infrastructure 
and considering ALAN within its boundaries: 
In a region in the Geneva basin in Switzerland, dark 
infrastructure has been created by intersecting low 
ALAN areas with the existing green infrastructure. 
This  was  done  by  an  automated  method  that 
extracted 
light  sources  from  high-resolution 
aerial photography taken at night. Using this data, 
researchers  modelled  the  visibility  of  these  light 
sources from any location within 1 km radius to 
give  an  estimate  of  the  level  of  ALAN  (Ranzoni 
et  al.,  2019).  Although  the  analysis  does  not 
consider data from direct lighting measurements, 
it  allows  for  a  first  large-scale  mapping  of  the 
night-time  continuum  and  highlights  the  areas 
benefiting  from  very  low  light  pollution.  The 
areas  with  low  levels  that  were  intersected 
with  green  infrastructure  were  considered  to 
be  dark  infrastructure,  requiring  protection  of  
darkness quality.

Figure  12:  Raster  map  showing  visibility  of  light 
sources  of  the  Geneva  basin.  Source:  Sordello  et  al., 
2022.Published with license by Elsevier B.V. Available 
via CC BY 4.0

 y Integrating ALAN in the design of a new green 
or  blue  infrastructure  from  the  outset:  In 
Douai, France, a dark infrastructure was identified 
from  scratch  –  this  was  done  by  establishing 
a  bat  activity  map  for  different  groups  of  bats, 
using 80 bat sound recorders during two nights. 
The map set out a hierarchy of activity levels to 
identify the areas of highest bat activity, which 
then formed the dark infrastructure. It was not 
translated into cores and corridors but into a set 
of dark ecological continuities. The three shades 
of blue on the map are related to the intensity of 
bat activity, where the darkest blue has the most 
intense  bat  activity  and  is  a  priority  for  further 
actions of preservation and restoration. 

7 

Aim for sobriety with regard to lighting, by lighting only when strictly necessary, by questioning the need for lighting in advance 
and by seeking alternatives as a priority

 
 
 
 
40

Figure 13:  A bat activity map in Douai, France. The three shades of blue are related to intensity of bat activity 
where least dark blue is low intensity and darkest blue is high intensity. Source: Sordello et al., 2022.

2.4.5.  Sustainable development / Multifunctionality of dark infrastructure 

To  support  environmental  protection  and  for 
ALAN  measurement  to  be  accepted  long-term, 
sustainability  needs  to  be  integrated  into  the 
design,  creation  and  maintenance  of  outdoor 
lighting. In general, when mitigating light pollution, 
a  reduction  in  energy  use  and  ecological  impacts 
will  also  follow,  and  often  initiatives  to  improve 
energy  efficiency  and  user  experience  can  lessen 
light pollution (Jägerbrand and Bouroussis, 2021a; 
Stockhammer, Zulka and Schindler, 2022). However, 
this  isn’t  always  the  case  and  there  is  a  need  to 
consider all aspects of sustainability in any lighting 
decisions.  Awareness  of  light  pollution  as  an 
environmental problem is relatively new compared 
to climate change and other forms of pollution, and 
there may be a need to increase recognition of its 
impact, and if necessary prioritise its management 
(Sordello et al., 2022). 

The example of traditional LEDs demonstrates how 
actions  to  improve  energy  efficiency  and  reduce 
carbon  can  have  negative  ALAN  consequences. 
There  are  already  technical  developments  to 
overcome the light pollution effects of traditional 
LEDs  (see  section  2.2.5),  but  management  also 
plays an important role, especially in the decisions 
made  around  light  installations.  These  must  be 
assessed from a sustainable perspective on social, 
economic  and  environmental  dimensions  and  all 
relevant  aspects  must  be  fully  considered  and 
assessed  through  indicators,  preferably  based  on 
a range of metric units. 

For example, a tool based on sustainability indicators, 
or  individually  chosen  indicators,  can  be  used  in 
mandatory requirements in the procurement process 
for  lighting  installations,  both  for  new  projects  and 
for the upgrading of old installations – at an EU level 
(Donatello et al., 2017) (see section 2.2.3 and Box 7). 

 
A    good  example  of  sustainable  lighting  design 
being  integrated  into  urban  design,  by  local 
government planners, can be found in the city of 
Rotterdam in the Netherlands, where all 100,000 
light  posts  are  currently  fitted  with  LED  fixtures 
that can be remotely adjusted for light intensity at 
any  time  of  the  night  (Jägerbrand  and  Spoelstra, 
2023). This enables responsive lighting, which can 
be adjusted to lower light levels when needed, such 
as times of the year when migratory, night flying, 
light sensitive species might be present. 

To enable efficient and sustainable exterior lighting, 
a  researcher  has  undertaken  an  examination  of 
the  synergies  and  trade-offs  in  these  two  areas. 
Through  applying 
indicators  spanning  social, 
ecological  and  economic  areas,  the  researcher 
can  then  assess  where  there  are  interlinkages 
and  therefore  the  potential  for  mutual  gains.  A 
literature review was conducted, revealing a total 
of 33 indicators (with 18 in the area of ecology and 
environment; 5 in the area of economy; and 10 in 
the area of social sustainability). 

The  study  found  most 
interactions  between 
variables for sustainable development and energy 
performance  (52%),  and  the  majority  of  these, 
(71%),  were  in  the  ecological  and  environmental 
dimension  showing 
that  environmental  and 
ecological sustainability can also equate to energy 
efficiency  and  savings.  The  study  lays  down  the 
foundations  of  assessing  interactions  between 
sustainable development and energy performance, 
to  establish  more  efficient  policies  for  decision-
making processes regarding exterior lighting.

More recently an analysis of lighting masterplans 
(see section 2.4.1) from 16 Swedish municipalities, 
identified 28 sustainability indicators, of which, ten 
were in the dimension of ecology and environment 
and,  18  were  in  the  social  and  society  dimension 
of  sustainability.  The  findings  showed  that  there 
is a need for guidelines and recommendations for 
working with outdoor lighting from a sustainability 
perspective,  especially  in  the  social  dimension, 
where most of the new indicators were identified. 

41

The  multifunctionality  of  green  and  blue 
infrastructure – where these ecological approaches 
bring multiple environmental, social and economic 
benefits  –  has  already  been  highlighted  to 
demonstrate  advantages  of  adopting 
these 
initiatives.  However,  at  present  there  is  limited 
research  available  to  provide  an  evidence  base 
regarding  the  multifunctionality  and  ecosystem 
services  of  dark  infrastructure  which  include 
ecological impacts.  

Cory's Shearwater Calonectris borealis fledgling picture was taken 
while  researching  factors  of  light  pollution-induced  mortality  in 
Tenerife, Canary Islands.  A critical phase in the life of a nesting-
burrow petrel is fledging – young birds leave their nest to fly to sea 
for  the  first  time,  normally  at  night.  Unfortunately,  thousands  of 
fledglings  are  disoriented  by  artificial  lights  around  the  world  in 
archipelagos such as Hawaii, Azores or Canary Islands. Once birds 
are grounded they are unable to take off again, and susceptible to 
death  by  vehicle  collisions,  starvation,  dehydration  or  predation. 
Source:  Airam  Rodríguez  (Estación  Biológica  de  Doñana  CSIC), 
CC  BY  4.0  <https://creativecommons.org/licenses/by/4.0>,  via 
Wikimedia Commons

 
42

Box 11: Case study: Targeted solution to protect marine birds using 
management and technological changes (Atchoi et al., 2021).

in 

the 
Light  pollution  on  urban  coastlines 
Macaronesian archipelagos of the Azores, Madeira 
and  the  Canary  Islands,  have  known  impacts  on 
seabirds.  Negative  impacts  on  seabirds  in  this 
region are most notable when juveniles leave their 
natal colonies for the first time, and are disoriented 
and attracted by artificial light at night (Rodríguez 
et al., 2017). Long-term rescue campaigns search 
for,  collect  and  release  fallen  juveniles.  Alongside 
there  has  been  an  increasing  number  of  actions 
to prevent or reduce light pollution, mostly centred 
on  the  critical  fledging  periods.  To  connect  these 
initiatives,  the  ‘LuMinAves’  project  was  designed, 
to  unite  efforts  across  regions,  and  provide  a 
common  platform  for  development  of  enhanced 
mitigation practices.

The  project  ran  from  2016  to  2020.  It  covered 
ten  petrel  species,  spanning  across  the  three 
archipelagos.  Mitigation  actions  pre-dating  the 
project were progressively applied throughout the 
region.  For  example,  on  Madeira,  a  pilot  project 
into  a 
integrated  sustainable  smart 
municipality urban plan. In the Azores the rescue 
campaign,  SOS  Cagarro,  partnered  with  private 
and  public  entities  to  turn  off  public  lights  in 
specific  areas  each  year  known  for  higher  fallout 

lighting 

(e.g.,  airport,  churches  and  industry  buildings). 
LuMinAves  enabled 
the  sharing  of  actions, 
procedures and outcomes, allowing direct learning 
and connectivity between partners. 

The  project  also  successfully  gathered  data  via 
monitoring  schemes.  Maps  depicting  the  spatial 
distribution  of  fallout  were  created  for  each 
island.  This  knowledge  was  used  to  inform  the 
design  of  light  pollution  management  strategies, 
and  enabled  the  incentivisation  of  illumination 
changes  to  improve  energy  efficiency  and  reduce 
light  pollution.  For  example,  regional  electrical 
companies  and  local  governance  associated  a 
certificate of good environmental practices to their 
urban lighting plans, facilitating the implementation 
of new measures. 

The project ended in December 2020, however, its 
actions  and  goals  extend  beyond  its  time  frame. 
Partners formed a working group which is working 
on regional regulatory legislation regarding lighting 
protocols. Likewise, a sequential INTERREG project 
will be building upon LuMinAves actions to continue 
the  efforts  towards  light  pollution  reduction  and 
research in Macaronesia. 

Box 12: Impact of Earth Hour on Urban Light Pollution in Berlin 
(Jechow, 2019).

The  WWF  Earth  Hour  campaign  has  grown  over 
the  years,  and  in  2018  was  celebrated  in  188 
countries.  It  calls  for  voluntarily  reduction  of 
electricity consumption for a single hour of one day 
each year. 

In  principle  the  switch-off  allows  for  the  study 
of  light  pollution  and  the  linkage  to  electricity 
consumption,  but  quantitative  analysis  is  sparse, 
with only a few studies showing no clear impact. 

Researchers have used a novel light measurement 
method,  using  differential  photometry,  with 
calibrated  digital  cameras  that  enable  tracking 
of the switching off and switching back on of the 
lights of Berlin’s iconic Brandenburg Gate, and the 
buildings of Potsdamer Platz adjacent to the park. 
This showed measurable light pollution reduction, 
despite the presence of moonlight. 

By using this approach, several places around the 
world  will  allow  similar  studies  that  can  provide 
insight  into  strategies  to  both  reduce  energy 
consumption and light pollution. 

43

Connected dark infrastructure projects at national level 

Several Dark Infrastructure projects have already 
been conducted in France as exploratory initiatives 
by  local  stakeholders  from  natural  sites  (national 
parks,  regional  nature  parks)  and  numerous  local 
authorities. France is a pioneer with this nocturnal 
ecological  network  initiative  and  has  over  60 
locations  where  activities  are  taking  place  to 
reduce  or  mitigate  ALAN8  Five  French  national 
parks (Cervennes, Pyrenees, Portcros, Mercantour, 

Reunion)  conducted  a  joint  project  to  map  their 
light  pollution  and  their  dark  infrastructure  and 
are now implementing their action plans to restore 
darkness  where  it  is  degraded  (Sordello,  Paquier 
and  Daloz,  2021).  Figures  7  and  8  illustrate  the 
work conducted by the Parc national des Pyrénées 
(PNP  -  Pyrenees  National  Park)  to  model  light 
pollution  within  the  national  park  and  to  map  its 
dark infrastructure. 

Figure 14: Map of light pollution modelled for the Pyrenees National Park.  Source: © 2022, Romain Sordello, Fabien 
Paquier and Aurélien Daloz, Published with license by Office français de la biodiversité - available and downloaded 
via Creative Commons licence 

8 

http://www.trameverteetbleue.fr/tramenoire

44

Figure  15:  Biodiversity  patches  affected  and  unaffected  by  light  pollution.  Source:  ©  2022,  Romain  Sordello, 
Fabien Paquier and Aurélien Daloz, Published with license by Office français de la biodiversité - available and 
downloaded via Creative Commons licence 

2.4.6.  Cross-cutting approaches focussed on species and ecosystems

Few  studies  focus  on  the  impact  of  artificial 
lighting  on  species  composition,  demography  or 
ecosystem function, which are all directly relevant 
to  conservation.  Current  research  provides  an 
estimate  of  impacts  on  species’  conservation 
based on their expected sensitivity or vulnerability 
(Jägerbrand  and  Bouroussis,  2021).  
to 

light 

There  is  an  agreement  about  the  specific  species 
and groups that are particularly affected by ALAN, 
but  not  necessarily  about  the  different  ways  in 
which  they  are  impacted,  and  what  can  be  done 
to lessen the impact. Some of the generic groups 
that have been identified as potentially being most 
sensitive to light are listed in Table 4.

 
45

Table  4:  Species  and  groups  that  may  require  higher  prioritisation  due  to  their  increased  sensitivity  to  light, 
or the risk of negative influence at sensitive periods in their life cycles. Source: Adapted from Jägerbrand and 
Bouroussis, 2021b.

Species and groups

Nocturnal or crepuscular species

Potential ecological impacts of artificial 
light at night (ALAN)

ALAN can result in decreased time and area 
for night-time activities important for survival, 
which can result in lower fitness and survival 
rates

Species living in vulnerable habitats

ALAN can have a particularly high impact

Species that migrate or move seasonally

Species with positive or negative phototaxis

Endangered species

Species that depend on key ecosystem 
functions that are impacted by ALAN

ALAN can result in unwanted impact on 
migration or seasonal movements, which are 
vulnerable periods in lifecycles i.e. Monarch 
butterfly

ALAN may cause ecological traps by attracting 
species with positive phototaxis i.e. moths 
drawn to a light, resulting in high mortality

ALAN may decrease the species area of 
activities, for species with negative phototaxis, 
i.e. some bat species that are repelled by 
lighting, lowering fitness and survival rates

ALAN may act as an additional disturbance, or 
cumulatively with other stressors, resulting in 
further degradation of habitats and a potential 
detrimental impact on species 

Ecosystem functioning can be affected by artificial 
light,  with  serious  consequences  for  habitat 
and  ecosystem  conservation.  For  example,  light 
pollution can affect pollination by nocturnal insects 
(Macgregor  et  al.,  2017)  resulting  in  disrupted 
pollen transport (see 2.4.6.2) and it may interrupt 
seed  dispersion. Research has also indicated that 
ALAN  can  impact  ecosystem  functioning  even 
outside of lit areas (Giavi et al., 2020). 

Indirect consequences of artificial light often arise 
from  a  competitive  advantage  or  disadvantage 
it  bestows  upon  a  specific  species.  
that 

For  example,  artificial  light  attracts  certain  fast-
flying  bat  species  that  feed  on  a  large  number 
of  insects  around  light  sources  (see  2.4.6.4).  The 
competitive  advantage  that  this  gives  to  certain 
bat  species  may  lead  to  an  unwanted  impact  on 
other  more  light-averse  bat  species  which  is  an 
issue  for  endangered  species  in  light-polluted 
areas (Hooker, Lintott and Stone, 2022).

Various measures have been developed to address 
the  impacts  of  light  pollution  at  the  species  or 
ecosystem  function  level,  which  take  specific 
conservation issues into consideration. 

46

2.4.6.1.   Measures to address light pollution at family, group and ecosystem level

Family focus:  marine turtles 

The Australian government has developed National 
Light  Pollution  Guidelines  for  Wildlife  including 
Marine Turtles, Seabirds and Migratory Shorebirds 
(Commonwealth  of  Australia,  2020).  The  ‘Light 
Pollution  Guidelines’  aim  to  raise  awareness  of 
the  potential  impacts  of  artificial  light  on  marine 
turtles, and provide a framework for assessing and 
managing  these  impacts  near  important  nesting 
beaches  (Arthur,  Whiting  and  Pendoley,  2020). 
This  framework  provides  consistent,  standardised 
and  transparent  processes  and  expectations  for 
assessing,  measuring,  auditing  and  managing 
artificial light around wildlife. 

Loggerhead  sea  turtle  hatchlings,  Carreta  carreta,  making  their 
way to the ocean. Cape Hatteras National Seashore. Source: Public 
domain, via Wikimedia Commons

regarding 

objectives 

Around  important  marine  turtle  nesting  beaches, 
the  Light  Pollution  Guidelines  recommend  an 
Environmental Impact Assessment (EIA) approach. 
This should include consideration of the biological 
artificial 
management 
light,  the  proposed  lighting  design,  mitigation 
and  a  risk  assessment  including  the  likelihood 
of  negative  consequence  to  nesting  marine 
turtles  or  hatchlings.  Light  management  must  be 
considered  on  a  case-by-case  basis  as  lighting 
conditions  are  geographically  dependent,  so  the 
guidelines do not prescribe specific light levels and 
mitigations.  The  success  of  light  management  is 
determined  by  whether  wildlife  can  continue  to 
engage in important behaviours, and effectiveness 
of  mitigation  should  always  be  reviewed  using 
biological monitoring and light auditing. 

Research  in  the  Mediterranean  has  suggested 
mitigation  measures  such  as  the  elimination  of 
unnecessary  lights,  the  use  of  long  wavelength 
lights,  the  shielding  of  light  sources  that  are 
directly  visible  from  a  beach  and  the  elimination 
of  all  upward-directed  lighting  (Dimitriadis  et 
al.,  2018).  Other  complementary  measures  may 
also  include  the  shading  of  nests  from  night 
lights  and  the  preservation  and  enhancement  of 
sand  dunes  and  beach  vegetation  (Dimitriadis  et 
al.,  2018).  Some  studies  are  evaluating  specific 
mitigation  approaches  for  specific  cases,  for 
example,  research  has  shown  that  fully  shielded, 
long-wavelength  LED  streetlight  fixtures  provide 
an appropriate option to minimize impacts to sea 
turtles  along  coastal  roadways  throughout  the 
United States (Long et al., 2022). 

Loggerhead  sea  turtle  hatchling,  Caretta  caretta,  taken  on  a 
Natura  2000  site  in  Kyparissia,  Greece.  Source:  Dionysisa303,  CC 
BY-SA  4.0  <https://creativecommons.org/licenses/by-sa/4.0>,  via 
Wikimedia Commons

 
2.4.6.2.   Group/ecosystem function focus: Insects, including pollinators

47

It  is  proposed  that  ALAN  has  been  driving  insect 
declines  in  combination  with  other  factors  such 
as  habitat  loss,  pesticide  use,  invasive  species 
and  climate  change  (Stockhammer,  Zulka  and 
Schindler,  2022).  The  effects  are  varied,  and 
range  from  disorientation  in  time  and  space, 
desensitisation  to  light  (dazzled  or  blinded),  and 
loss  of  ability  to  discriminate  colours.  There  is 
concern  that  the  increased  usage  of  white  LEDs 
will  impact  insects  as  they  are  more  sensitive  to 
short  wavelengths.  One  group  that  is  particularly 
prone to negative effects of ALAN are moths, and 
research  has  shown  that  light  pollution  affects 
their reproduction and development. In turn, it also 
affects the composition of moth assemblages and 
the ecosystem functions they perform.  

The EU Pollinators Initiative is the first ever EU action 
framework to tackle the decline of wild pollinators. 
A  workshop  took  place  online  in  2022,  which 
aimed to strengthen actions to enhance pollinator-
friendly artificial night lighting in Europe,  through 
the  existing  Pollinators  Initiative  (Stockhammer, 
Zulka  and  Schindler,  2022).  Organised  by  DG 
Environment and the German Environment Agency 
(Umweltbundesamt),  the  workshop  was  aimed 
at  experts  across  stakeholder  groups,  including 
public authorities, practitioners engaged in spatial 
planning,  innovation  and  social  change  experts, 
academia, land managers and non- governmental 
organisations

The  resulting  revised  EU  Pollinators  Initiative 
was  released  in  January  20239,  recommending 
member  states  to  mitigate  the  impact  of  light 
pollution  through  national  and  regional  policies. 
initiative  also  highlighted  the 
The  updated 

Commission’s  new  guidelines  on  light  pollution 
mitigation  for  cities10  and  citizens  for  pollinator 
conservation11. The revised EU Pollinators Initiative 
integrated 
states  that  the  Commission  has 
recommendations  on  how  to  mitigate 
light 
pollution into its guidelines for citizens and cities, 
and  will  continue  to  promote  them  (European 
Commission,  2023).  More  specific  details  on  the 
guidelines  directed  at  mitigating  the  impacts  of 
ALAN on pollinators can be seen in Box 11.

Butterflies near a light bulb. Source: https://www.shutterstock.
com/image-photo/butterflies-old-lamp-58175626

2.4.6.3 Class focus: Birds – mitigating impact of ALAN inland 

The City of Toronto in Canada received a Bird-friendly 
certification from Nature Canada for adopting best 
practice  in  effective  lighting,  to  reduce  negative 
impacts  on  birds.  The  City  of  Toronto,  worked 
closely  with  Fatal  Light  Awareness  Program 
(FLAP)  Canada,  to  keep  birds  safe  from  deadly 
collisions  with  buildings,  and  developed  a  set  of 

guidelines on best practices to protect birds with 
regard to glass12.

In the guide reflective glass, particularly surrounded 
by vegetation is a particular problem for bird collisions 
–  as  the  reflective  glass  mirrors  the  surrounding 
vegetation,  such  as  trees.  Forest  dwelling  bird 

EUR-Lex - 52023DC0035 - EN - EUR-Lex (europa.eu)

9 
10  https://wikis.ec.europa.eu/display/EUPKH/Cities 
11  https://wikis.ec.europa.eu/display/EUPKH/Citizens 
12  https://www.toronto.ca/wp-content/uploads/2017/08/8d1c-Bird-Friendly-Best-Practices-Glass.pdf

 
48

species  that  feed  near  to  canopies  were  the  most 
likely to collide (City of Toronto, 2016).

The bird friendly building programme was developed 
by  FLAP  Canada  and  the  World  Wildlife  Fund 
Canada,  to  address  light  pollution  from  buildings 
and  reduce  bird  mortality.  When  bird  friendly 
practices were adopted by building managers and 
tenants  of  some  buildings  in  Toronto,  they  were 
shown to have a significant effect at reducing the 
number  of  birds  killed.  Light  emission  reduction 
was  mostly  from  tenant  awareness  programmes, 
but  computer-controlled  lighting  systems  were 
also used in some buildings. 

in 

interventions  suggested 

the 
Architectural 
Toronto,  glass  guide,  include,  building-integrated 
structures  that  obscure  glass  from  view,  mute 
reflections  during  certain  times  of  the  day  and 
provide visual cues for birds to avoid an area. These 
structures  include:  opaque  awnings,  sunshades, 
exterior screens, shutters, grilles and overhangs or 
balconies that provide shading below a projection. 
Other building guidelines include visual markers on 
the glass at regular intervals, coupled with opaque, 
matt  materials  on  the  glass  to  stop  reflection. 
Guidance is tailored to the features of the building 
and surrounding vegetation.

Top: Migrating bird carcasses, killed by colliding with buildings. Bottom: Birds killed during the migration season in 2013 in Washington 
D.C.  The  birds  were  picked  up  by  the  group  ‘Lights  Out  Washington  D.C.’  and  include  species  such  as  Worm-eating  Warlblers,  Scarlet 
Tanagers, American Woodcock, Saw whet Owl, Coopers Hawk, Black and White Warbler, Swamp Sparrow, Song Sparrow, Ruby-throated 
Hummingbird and other. Source: USGS, Native Bee and Inventory and monitoring programme, creative commons license, public domain. 
Flickr, CC BY 2.0- photos by Sam Droege

49

Figure 16: Global Bird Collision Mapper, by FLAP Canada, shows number of bird collisions reported via this portal 
form around the world. This Citizen Science resource offers insight into the breadth of these collisions. Source: 
https://www.birdmapper.org/pages/explore-the-map

2.4.6.4.   Seeing the bigger picture – impact of ALAN and its management on bats (Hooker, Lintott 

and Stone, 2022)

roosts  and 

Linear  habitat  features  such  as  waterways 
are  important  for  bats.  Water  surfaces  and 
the  vegetation  provides  foraging  habitats  and 
waterways  also  act  as  commuting  corridors 
linking 
foraging/drinking  areas 
(Smith and Racey, 2008; Lacoeuilhe et al., 2016; 
Pinaud et al., 2018). Waterways are particularly 
important  for  a  number  of  slow-flying  bat 
species (e.g. Myotis spp.) that have echolocation 
and  wing  morphology  adapted  for  cluttered, 
low-light  environments.  These  habitats  are 
increasingly experiencing light pollution. 

Part-night  lighting  (PNL)  involves  switching  off 
street-lights during periods of low human activity 
and has been implemented widely in urban areas 
throughout  Europe,  mainly  to  reduce  energy 
usage  but  also  to  limit  light  pollution.  Studies 
of  PNL  have  looked  at  the  impacts  of  PNL  on 
numbers  of  bats  but  have  not  drilled  down  into 
important details of conservation such as feeding 
behaviours or bat assemblages. 

treatments. This suggests that, to some extent, PNL 
limits  the  negative  impacts  of  ALAN  by  allowing 
Myotis  bats  to  have  peaks  of  activity  later  in  the 
night after lights are switched off. Superficially this 
may  seem  to  highlight  the  efficacy  of  PNL  as  a 
mitigation method, however the results show that 
this is not true for all behaviours. For example, there 
was a 50% reduction in relative feeding activity in 
the  PNL  treatment  suggesting  that  PNL  reduces 
the feeding activity window for these species. 

The results indicate that, despite being a valuable 
approach  in  terms  of  reducing  carbon  emissions 
and public sector costs, PNL schemes are unlikely 
to  provide  desired  biodiversity  benefits  especially 
for bats due to species-specific impacts on activity 
and  feeding.  Therefore,  if  the  aim  it  to  limit  the 
negative  impacts  of  ALAN  on  biodiversity,  it 
would  be  more  beneficial  to  pursue  alternative 
management  strategies  such  as  reducing  light 
trespass,  changing  the  intensity  or  spectrum  of 
lighting and increasing dark corridor networks.

Recent  research  has  provided  a  more  detailed 
evaluation of PNL and shown that overall activity 
under full-night light treatments was significantly 
lower in comparison to both unlit nights and PNL 

Building  on  this  insight,  it  may  be  best  to  use 
different combinations of management strategies. 
There have been several initiatives at regional and 
national  levels  to  address  the  negative  impact 

50

of  ALAN  on  bats  that  recommend  a  combination 
of  technological  and  management  strategies, 
depending  on  which  species  are  present  and 
which  behaviours  the  light  pollution  could  affect 
(roosting,  feeding,  reproduction  etc.)  The  UNEP/
EUROBATS Guidelines for consideration of bats in 
lighting projects (Voigt, C.C et al, 2018) sets out a 
range  of  recommendations  to  avoid,  mitigate  for 
and  compensate  both  direct  and  indirect  effects 
of  lighting  schemes,  which  focus  on  the  different 
behaviours that ALAN might disrupt. 

importance 

Similarly,  the  Bats  and  Artificial  Lighting  in  the 
UK  Guidance  Note  outlines  a  simple  process  to 
consider the impact on bats as part of a proposed 
lighting scheme. It contains techniques which can 
be used on all sites in a stepwise process, starting 
with  establishing  the  presence  or  absence  of 
bats,  and  presence  of  roosting  habitat,  foraging 
habitat  and  their 
(Institution  of 
Lighting Professionals and Bat Conservation Trust, 
2018).  Seeking  the  assistance  of  local  ecologists 
is  directed  when  bats  are  present,  to  conduct 
surveys.  Avoidance  of  illumination  of  key  habitat 
features  is  noted,  with  this  being  a  requirement 
for  roost  entrances  and  flightpaths  particularly, 
especially when rare or light averse bat species are 
present. When a development is proposed near to 
bat habitat, mitigation measures are advised under 
the  guidance  of  an  ecologist,  with  any  lighting 
designed to be within lux limits and designed by a 
lighting professional.13

13 

layout (bats.org.uk)

Lesser  horseshoe  bat  (Rhinolophus  hipposideros)  roosting  under 
the  stairs  in  a  church  tower.  Source:  Lesser  horseshoe  bat 
(Rhinolophus  hipposideros)  bats  roost…  |  Flickr  ©  Flickr,  CC  BY 
2.0- photo by Jessicajil

 
 
51

3.  Monitoring ALAN remotely

There  have  been  advances  in  a  number  of 
monitoring methods, especially in the use of remote 
sensing. Research opportunities are emerging with 
the development of new space borne, airborne and 
ground sensors for quantifying light at night (Levin  
et al., 2020). 

In  particular  satellite  data  has  attracted  growing 
interest  where  images  of  the  Earth’s  surface 
are  taken  from  space  at  night  and  can  provide 
information  on  the  distribution  of  light  emissions 
(see  box  13).  However,  there  are  a  number  of 
considerations  that  need  to  be  considered  in  the 
use  of  this  satellite  data.  The  images  are  taken 
from  above,  and  at  distance,  which  means  a  key 
component  to  improving  the  utility  of  the  insight 
they  can  provide  is  the  translation  of  remotely 
sensed  values  to  a  ground  level,  where  light 
pollution may be experienced differently.  

Satellite  data  is  also  highly  dependent  on  the 
weather  conditions,  such  as  cloud  cover  (Kyba  
et  al.,  2011).  For  example,  in  areas  with  little  or 
no  artificial  lighting,  clouds  darken  the  night  sky, 
while  in  areas  with  artificial  lighting  they  make 
it  considerably  brighter  (Levin  et  al.,  2020).  Snow 
cover also has the potential to significantly increase 
the luminance of the sky by reflecting any type of 
lighting (Jechow & Hölker, 2019b).

Field data can ground truth satellite observations 
(Levin  et al., 2020), and one solution is to compare 
ground-based night sky brightness measurements 
using,  for  example,  sky  quality  meters  (SQMs). 
These can either be directly compared to the light 
observed from space, or to the results from models 
of sky brightness that based on the satellite data 
(Wallner  &  Kocifaj,  2019).  Low-cost  night  light 
radiometers such as SQMs, and the use of mobile 
phones to collect data, have expanded the number 
of surveyed sites on the ground, and enabled the 
active participation of citizen scientists in research 
(see  section  3.1)  to  provide  this  comparison  with 
ground data. However, SQM measurements can be 
influenced by numerous factors in the surrounding 
environment,  for  example  reflection  of 
light 
from  vegetation  can  affect  night  sky  brightness 
(Puschnig et al., 2023). Also, the use of SQM meters 
for longer term measurements and monitoring of 
night sky brightness changes, requires corrections 

to  data  to  account  for  aging  effects  such  as  the 
sensor degrading (Puschnig et al., 2021). 

Advances in remote sensing have enabled a wider 
coverage  of  data  collection  on  night  lighting,  but 
there  are  various  locations  and  environments 
that  are  notably  less  monitored  than  others.  For 
example,  citizen  science  cataloguing  of  the  ISS 
night-time  photos  has  highlighted  that  they  do 
not represent all parts of the world, and are more 
common  in  the  urban  areas  of  North  America, 
Europe, the Middle East, eastern China and Japan. 
Satellite  data  on  ALAN  for  Europe  comes  largely 
from one satellite that covers Europe, with a spatial 
resolution of 1km, however nearer to the equator 
this lessens to around 2.7km (Bennie et.al., 2015). 
Additionally,  the  European  satellite  isn’t  always 
overhead at the correct time, with northern Europe 
having less coverage. With more recent technology, 
satellites  can  now  achieve  a  spatial  resolution  of 
5m  (see  box  13)  the  capabilities  of  monitoring 
ALAN may improve.

installations  emitting 

An  increasingly  important  issue  is  that  satellites 
have  difficulties  detecting  LED-lighting  systems, 
especially 
lights  with 
wavelengths  below  500  nm.  Blue  light  scatters 
more than red or yellow light, which makes it more 
difficult  for  the  satellite  to  capture  these  light 
emissions and the measured values of light at lower 
wavelengths are less accurate (Pérez Díaz  et al., 
2021).  This  may  result  in  optimistic  assessments 
of reductions in light pollution (Kyba  et al., 2017), 
however new approaches using mobile phones are 
enabling  monitoring  of  light  across  the  spectrum 
(see box 14). 

Monitoring  of  ALAN  remotely  is  associated  with 
some  limitations.  For  instance,  the  integration  of 
satellite  data  with  ecological  data  in  both  spatial 
and  temporal  dimensions  presents  challenges 
to  mitigate  discrepancies.  This  arises  from  the 
dynamic nature of night time light, whereas satellite 
imagery often relies on composites generated over 
extended  periods  of  time,  such  as  two  weeks  or 
summarized  over  a  year,  to  construct  images. 
Responses  to  light  by  living  organisms  is  often 
direct  and  highly  local,  for  instance  for  species 
with  positive  phototaxis  and  such  responses  may 
be  difficult  to  match  with  large-scale  monitoring. 

52

Long-term light exposure is more likely to degrade 
habitat  quality,  making  it  challenging  to  attribute 
these effects directly to light pollution impacts. 

Moreover, the issue of scale merits attention. There 
is  a  lack  of  comprehensive  studies  evaluating 
the  applicability  of  satellite-derived  data  at 

local  scales  compared  to  larger  scales.  Local-
scale  considerations  are  particularly  pertinent  to 
numerous  terrestrial  organisms,  however  when 
considering  aerial  and  migratory  species  it  may 
be more important to have data at a larger scale 
(Simons et al., 2020). 

Box 13: Advances in satellite data (Pérez Díaz et al., 2021)

The  Visible  Infrared  Imaging  Radiometer  Suite 
(VIIRS)  sensor  onboard  the  Suomi  NPP14  was 
launched  in  October  2011,  and  has  been  fitted 
with a specific pan- chromatic sensor designed for 
measuring  night  time  lights  –  the  Day  and  Night 
Band (DNB). The VIIRS/DNB presents a significant 
improvement  over  the  previous  sensor,  in  data 
availability, in its higher spatial resolution (740 m, 
instead of about 3 km), in providing calibrated data 
which is sensitive to lower light levels and does not 
saturate in urban areas.

The  first  commercial  satellite  with  high  spatial 
resolution  night-time  capabilities  (at  0.7  m),  was 
the  Israeli  EROS-B  satellite,  which  was  launched 
in  2006,  but  only  started  offering  night-  time 
acquisition  publicly  in  2013  (Levin,  et  al.,  2014). 

The first commercial satellite to offer multispectral 
(red, green and blue) night-time lights images (at 
0.92 m) was launched in 2017: the Chinese JL1-3B 
(Jilin-1) satellite. 

Cubesats, a class of miniaturised satellites, are a 
relatively  new  development,  consisting  of  10  cm 
cubes.  Another  satellite  which  offers  the  public 
global  images  of  many  regions  on  Earth  at  night 
is LJ1-01 (Luojia-1). Luojia-1, was built by Wuhan 
University  and  launched  in  June  2018,  providing 
night- time images at 130m spatial resolution. Most 
recently, the Luojia-3 has been launched, which has 
a faster transmission speed, and greater accuracy 
of  target  detection,  enabling  real-time  streaming 
of images. Importantly, it can also handle most of 
the data processing and analysis itself.

3.1.  Making sense of data with citizen science

For  data  on  ALAN  to  be  valuable  in  informing 
mitigation and prevention strategies, it needs to be 
at scale, and in a form that can be analysed. There 
have been huge advances in the level, and speed 
of data processing, however, remote sensing data 
from sources such as satellites and space stations, 
usually requires some form or parsing, categorising 
or  connecting  of  data  to  make  it  relevant  for 
light  pollution  analysis.  Citizen  science  has  been 
playing a key role in enabling this to happen, and 
in collection of other ground-based data (Kyba  et 
al., 2013).

(ISS)  provide 

Currently,  the  astronaut  photographs  from  the 
International  Space  Station 
the 
largest  online  archive  of  night-time  images  of  the 
Earth15. However, these images lack precise location 
and  georeferencing.  A  citizen  science  program 
called  “Cities  at  Night”  has  provided  an  improved 
catalogue of night-time images from the ISS (https://
citiesatnight.org). With the collaboration of more than 
20,000 volunteers, the project has tagged more than 
190,000  nocturnal  images  of  mid  and  high  spatial 
resolution (resolution from 5 to 200 m) and the data 
has  been  used  on  several  papers  concerning  light 
pollution monitoring (de Miguel  et al., 2014). 

14  The Suomi National Polar-orbiting Partnership (Suomi NPP)  is a weather satellite operated by the United States National 

Oceanic and Atmospheric Administration (NOAA). It was launched in 2011 and is currently in operation. The Visible Infrared 
Imaging Radiometer Suite (VIIRS) is the largest instrument aboard of Suomi-NPP and collects radiometric imagery in visible and 
infrared wavelengths of the land, atmosphere, ice, and ocean.

15  Photographs of the Earth at night taken from the International Space station, available from: https://eol.jsc.nasa.gov

53

The  recent  introduction  of  low-cost  night  light 
radiometers,  starting  with  the  Sky  Quality  Meter 
(SQM),  has  enabled  rapid  monitoring  of  night-
time brightness while walking, cycling or driving to 
allow monitoring of temporal changes in night sky 
brightness.  The  most  widespread  citizen  science 
projects using SQMs is “Globe at Night” (Walker  et 
al., 2007) which has been running since 2006. 

In  addition  to  instrumental  observations,  citizen 
scientists are able to make visual observations of 
night sky brightness by examining stellar visibility. 
While  visual  observations  have  lower  precision 
than instrumental observations (Kyba  et al., 2013), 
they  have  the  advantage  of  correctly  accounting 
for spectral changes in night sky brightness due to 
changing  lighting  technology  (Sánchez  de  Miguel  
et  al.,  2015).  Projects  using  mobile  phone  data 
collected  by  citizens  are  also  enabling  spectral 
analysis of night light (see box 14). 

Figure  17.  (a)The  number  of  night  time  ISS  photos 
identified  by  the  ‘Cities  at  Night’  crowdsourcing, 
citizen  science  project  within  100x100  grid  cells.  (b) 
The number of night time Luojia-1 images acquired so 
far  (8675,  in  May  2019)  with  250x250km  grid  cells. 
Source: Levin, et al., 2020. ©2023, Noam Levin

 
54

Box 14: NightUp citizen science project – extracting colour data  
(Muñoz-Gil  et al., 2022)

The NightUp citizen science experiment is collecting 
information  about  the  spatial  distribution  of 
colour  of  artificial  lights  at  night.  Using  a  cross-
platform mobile application, users take photos of 
streetlights  and  an  algorithm  detects  the  lamps 
in  the  photos  and  extracts  their  colour.  In  order 
to  compare  results,  the  devices  would  ideally  be 
calibrated, but it is unrealistic to assume each user 
could calibrate their own device or that researchers 
could do it for each model available on the market. 
As  such,  the  study  assumed  the  calibration  that 
smartphone  cameras  undergo  to  meet  the  ISO 
standards would be sufficient to obtain satisfactory 
results. With the geolocation of the NightUp data, 
it  can  be  used  to  create  maps  that  display  the 
colour of lamps in different regions. The first pilot 
of  NightUp  was  conducted  near  Barcelona  where 
researchers  had  an  updated  streetlight  database 
containing  information  on  the  geolocation  and 
the  lamp  technology  (e.g.,  high-pressure  sodium 
or  LED)  for  each  streetlight  in  the  city.  This 
enabled researchers to test the accuracy and data 
acquisition  of  NightUp  in  various  conditions,  as 
well  as  the  colour  extraction  algorithm  and  the 
pilot  showed  that  an  estimation  of  the  colour  of 
artificial light at night that was sufficiently precise 
to  distinguish  warmer  light  sources  from  colder 
ones. In the future this information could be used 
by local governments to optimize outdoor lighting 
and address light pollution problems as well as by 
scientists to study the effect of the colour of light. 
The NightUp data could also be used to efficiently 
calibrate satellite images to improve the precision 

of ecological and economical parameters extracted 
from  them.  Furthermore,  because  of  its  minimal 
technical  requirements,  the  researchers  believe 
that  NightUp  can  potentially  expand  to  a  global 
scale with the support of successful engagement 
strategies,  allowing  scientists  to  access  and 
characterise vast regions. However, it still needs to 
assessed if the NightUp approach will work for new 
and spectral tunable light sources. 

Figure  18.  Top  row:  Three  examples  of  light  source 
location  by  means  of  the  NightUp  algorithm.  Bottom 
row: The area in the rectangle of the image is cropped, 
and the circle in the bottom right hand corner showed 
the  colour  assigned  to  each  lamp.  Source:  ©  Gorka 
Muñoz-Gil, Alexandre Dauphin, Federica A. Beduini, and 
Alejandro Sánchez de Miguel, Published with license by 
MDPI - via Creative Commons licence

55

4.  Emerging issues in improving research approaches 
to ALAN, and knowledge gaps on impacts and 
mitigation 

As  discussed  in  previous  chapters,  a  number  of 
context  specific  mitigation  measures  are  already 
in place worldwide, which seem to be ameliorating 
the  negative  impact  of  light  pollution  on  certain 
species,  or  groups  of  species.  In  addition,  more 
general mitigation approaches are emerging, such 
as  shielding  light  fixtures,  or  only  using  them  at 
certain  times.  In  the  short  term  these  measures 
appear  to  have  had  some  positive  impacts  on 
target  species.  For  example,  in  New  York,  the 
Twin  Towers  memorial  lights  were  attracting 
migratory  bird  species,  but  these  are  now  turned 
off intermittently to allow trapped birds to escape 
(Jägerbrand and Spoelstra, 2023). 

Yet Jägerbrand and Brutemark, 2022, urge caution 
in  assuming  that  some  of  the  more  generalist 
mitigation  approaches  are  always  the  best  way 
to  lower  ALAN’s  harmful  ecological  impacts  on 
biodiversity. Instead, they suggest these measures 
should only be used with long-term monitoring and 
assessment alongside, to note the impacts on all 
species – not just the most photosensitive groups 
in  aquatic  and  terrestrial  habitats.  Monitoring 
of  these  mitigation  measures  should  include  a 
consideration  of  ecology,  demography,  migration, 
the  various  stages  in  species  lifecycles  and 
interactions with prey and predator and how these 

are  affected  by  light  at  night  (Jägerbrand  and 
Brutemark,  2022).  By  incorporating  well-planned 
monitoring  studies,  alongside  the  introduction 
of  these  mitigation  measures,  it  is  possible  to 
determine the baseline measurements for species 
prior to the introduction of mitigation measures, to 
demonstrate  evidenced-based  success  or  failure 
of the mitigation strategies. 

Jägerbrand and Brutemark, 2022, suggest research 
on the effectiveness of some of the more popular 
mitigation strategies that are being adopted on a 
large scale should address the following questions:

1.  Which  species,  ecosystems  and  ecological 
processes will benefit the most, and the least, 
from  popular  general  strategies  to  mitigate 
light pollution?

2.  How much will responses to ALAN differ between 
species  (with  various  photo  sensitivities),  as 
well as between ecosystems?

3.  Do  established  applications  (or  adaptations) 
in light installations or conservation measures 
have the intended mitigating effects on species, 
biodiversity and ecosystems?

4.  How can we measure ecological light pollution?

4.1.  Establishing standardised thresholds, measurement protocols and 
mitigation guidelines

The interdisciplinary nature of ALAN research has 
resulted  in  different  measurement  approaches, 
procedures  and  use  of  various 
light  units. 
The  research  community  continue  to  call  for 
standardised 
to  enable 
light  measurements 
comparison  across  the  disciplines  (Hölker  et  al., 
2021).  In  addition,  the  researchers  should  also 
provide  accurate  records  of  how  measurements 
of  ALAN  were  taken,  with  which  equipment  and 
from which position – for example holding a light 
meter  upright  at  shoulder  height  or  horizontally 
from  a  position  at  tree  height.  This  will  vary 
depending on the area being investigated, sources 
of  light  pollution  and  behaviour  of  concerned 

species  or  taxa.  These  would  undoubtedly  help 
in  the  establishment  of  recommended  technical 
measures  but,  in  reality,  it  is  unlikely  that  one 
single approach and unit will emerge that will suit 
everyone’s needs. 

Ecological  studies  on  ALAN  should  use  SI 
(international  standardised  system)  units 
to 
quantify light, however, there are advantages and 
disadvantages to the different ways of measuring 
light, and the prioritisation of these pros and cons 
will depend on the context of application (Widmer 
et al., 2022). As such, flexible measurement options 
are helpful as they enable bespoke mitigation and 

56

prevention strategies for different aspects of light 
pollution,  such  as  location,  spatial  scale,  existing 
policy, target species and functions of light.

light 

To  develop  effective  mitigation  measures, 
measuring 
in  a  standardised  manner 
and  addressing  research  gaps  are  needed.  In 
addition,  further  research  measuring  light  for 
local conditions on the ground is required – rather 
than  relying  only  on  satellite  data,  which  shows 
light emitted into space rather than light emitted 
below  a  forest  canopy,  or  towards  the  ground 
(Jägerbrand and Brutemark 2022). Although some 
species  are  impacted  by  light  directed  upwards 
–  such  as  nocturnally  migrating  bird  species  and 
avian  orientation  –  most  species  are  exposed 
to  light  emitted  below  the  horizontal  plane,  into 
light-sensitive habitats such as aquatic habitats or 
nature reserves (Jägerbrand and Brutemark 2022).

For  example,  to  investigate  ALAN  impacts  on  a 
small terrestrial mammal, such as a vole, one would 
need to measure light in the relevant exposure area 
–  for  example,  on  the  ground  in  the  directions  in 
which the animal may be looking. One would also 
need to quantify the light in units of relevance for 
the target organism, probably combining radiance 
with the spectra distribution, and then analyse the 
data  depending  on  which  spectra  the  organisms 
perceive the most. In addition, one should measure 
the ambient light at the study area in different parts 
of the study area and at different times, recording 
factors  that  might  influence  the  measurements, 
such as the phase of the moon, presence of clouds 
and other abiotic factors.

Measuring local light environments that are known 
to impact species, in a standardised manner, would 
aid in establishing the impact of intensity, timing, 
spectra and other aspects of ALAN on species and 
habitats. This would also be the start of establishing 
useful thresholds to improve mitigation measures 
based on accurate field data. 

Standardisation  to  restrict  spill  light,  is  urgently 
needed  to  prevent  the  negative  effects  of 
unintentional  lighting  in  vulnerable  habitats  such 
as  open  aquatic  environments  (Jägerbrand  and 
Spoelstra,  2023).  Overall  improved  guidelines 
on  standards  of  lighting  in  different  areas,  which 
consider  the  harmful  ecological  impacts  of  ALAN 
are required – to stop the excessive use of light – 
as is often the case at present.

Although  research  into  the  impacts  of  ALAN 
on  ecosystems  has  grown  considerably  over 
the  last  10  years,  there  are  still  a  number  of 
knowledge  gaps  which  require  further  research. 
These research gaps were summarised in a 2021 
review  for  Frontiers  in  Ecology  and  Evolution, 
by  Spoelstra  and  10  colleagues,  who  distilled 
them  into  11  research  questions  covering  ALAN-
sensitive species traits through to interactions with 
other stressors, such as climate change. However, 
most  of  these  questions  are  building  research 
knowledge  over  the  longer  term,  which  supports 
the identification of effective mitigation measures 
for ALAN, but is less pertinent to current solutions. 
However, some of the questions listed by Spoelstra 
et  al,  2021,  are  more  directly  related  to  current 
mitigation  measures,  for  example,  harmonising 
light measurement across disciplines – as discussed 
above  –  as  well  as  identifying  the  opportunities 
and challenges for effective management of ALAN 
(Spoelstra et al., 2021).

Establishing  the  ALAN  intensity  thresholds  of 
many  species,  is  highlighted  by  Jägerbrand  and 
Spoelstra  as  an  area  needing  more  research 
data.  The  ALAN  intensity  thresholds  of  species 
can  vary  between  species,  but  also  according  to 
exposure  duration,  life-history  stage  and  habitat 
structure.  To  translate  research  more  directly 
into  ecological  protection,  research  should  aim 
to  establish  a  numerical  threshold  value  on  the 
bases of illuminance or luminance of current light 
sources  and  technologies.  If  researchers  adopt 
this approach, it will allow research to be directly 
translated 
lighting 
design, and retrofitting/upgrading existing lighting 
systems (Jägerbrand and Spoelstra, 2023).

into  guidelines  for  future 

Further  research  on  environmental  lighting  zones 
would  be  of  benefit,  with  Zilienska,  et  al.,  2023, 
suggesting  there  is  currently  no  evidenced-based 
consensus on the maximum light levels allowed in 
outdoor urban residential areas to limit light spill.

It is clear that there is not a one size fits all approach 
to mitigating the effects of anthropogenic (artificial) 
light  on  all  species.  Monitoring  the  effectiveness 
of  different  types  of  mitigation  measures,  and 
combinations  of  these,  for  different  taxa  and 
environments, is an area which will require further 
research.  Technological  solutions,  in  the  form 
of  tuneable  spectra  LED,  dimmable  lighting  and 

57

sensor  timing  systems,  alongside  better  lighting 
design  incorporating  shielding  and  shutters,  have 
all helped to mitigate the impacts of ALAN in areas 
that  require  lighting.  However,  we  do  not  have 

technical solutions to all environmental challenges 
posed  by  ALAN,  and  need  engineers  and  lighting 
designers to help to create luminaire systems that 
further reduce reflection, glare and light spill.

Interdisciplinary research on the effectiveness of measures for 

4.2. 
mitigating the impacts of ALAN

Mitigating  measures  should  always  be  considered  as 
a last resort, with the first position being that natural 
darkness  is  preferential  in  most  circumstances.  For  a 
mitigation measure to be required, there needs to have 
been careful consideration and justification given as to 
why artificial light is required at all in a given location. 
The default position should always be that no artificial 
light is present at night, and planners should be seeking 
a justification as to why artificial light is needed when 
installing  any  new  luminaires.  The  justification  will 
usually be around human safety with regard to road, car 
park, or street lighting. However, in these circumstances 
the minimal amount of light required should be installed 
with shielding and on a timer to enable periods when 
they can be switched off – for example when important 
migratory species are present. A consideration of light-
vulnerable  protected  species  should  also  be  made,  if 
they are present in the surrounding habitat (see boxes 2 
and 7 for more detail).

In  order  to  improve  technical  and  management 
approaches  to  reducing  the  environmental  harm  of 
ALAN, there needs to be continuing evaluation to feed 
back  into  further  development  and  improvement. 
As  outlined  in  the  framework  for  dark  infrastructure  
(Sordello  et  al.,  2022),  this  will  involve  comparison 
before and after implementation of a given mitigation 
measure, with indicators related to light pollution and 
those  related  to  biodiversity.  Biodiversity  indicators 
need  to  combine  different  aspects,  including  species 
richness,  abundance  and  community  functioning  (life 
traits, relationships between species). 

To  develop  effective  indicators,  research  is  needed 
to  explore  questions,  such  as:  how  does  ALAN  alter 
biodiversity  by  redistributing  species;  how  does  ALAN 
affect  biodiversity  through  indirectly  altering  species 
interactions; and lastly, what are the effects of ALAN on 
biodiversity at the ecosystem and the landscape level? 
(Hölker et al., 2021).  

It  is  necessary  to  identify  indicator  species  –  often 
rare  or  protected  species  that  are  among  the  most 
vulnerable  nocturnal  animal  groups  to  ALAN  –  such 

as  bats,  amphibians,  nocturnal  Lepidoptera  i.e.  moths 
such as noctuid or sphingid moth and Lampyrid beetles 
– for different types of habitats/ecosystems. However, 
the reactions of these species to light may be quick and 
direct, whereas other species may be impacted over the 
long term, with notable changes in species composition 
at  the  ecosystem  level.  Given  the  differences  known 
so far in species responses to spectra and intensity of 
ALAN, a simple solution to mitigating the effects of light 
on  all  species  is  unlikely  (Jägerbrand  and  Spoelstra, 
2023).  Thus,  it  is  useful  to  investigate  different  types 
of mitigation measures and their impacts on taxa, as 
well  as  looking  to  successful  examples  of  mitigation 
measures in differing habitats, as presented above. 

There is a lot of research regarding ALAN mitigation and 
LED technology, with the general consensus being that 
future LED installations should ideally use light fixtures 
that  are  dimmable,  tuneable  and  respond  to  a  timer. 
Further  research  on  a  number  of  ALAN  variables  is 
needed, including a multitude of aspects of just two of 
these: colour and intensity of light emitted: responses of 
organisms to these over time (day, season), and impacts 
on  biodiversity  in  different  habitats.  Monitoring  data 
demonstrates that ALAN is present in many areas, such 
as underwater habitats at night – but more research is 
needed on the impacts of this across species in a dose-
effect manner, i.e. increasing light intensity, or changing 
colour spectra of emitted light. 

The  use  of  blue/white  light,  however,  has  an  impact 
on a wide variety of terrestrial and marine taxa, with 
insects  particularly  impacted.  Amber  lighting  has 
been proposed as a solution to this by the Dark Skies 
Consortium  and  the  IUCN,  and  even  red  lighting  in 
some  situations  such  as  in  installations  in  marine 
areas,  or  to  prevent  disturbance  to  most  bat  species. 
However, caution in this regard has been suggested by 
Jägerbrand  and  Spoelstra,  in  their  2023  review,  who 
note that in using highly adapted spectra – such as red 
lighting – you may create an ecological trap for species 
that are unable to sense this light and therefore become 
more vulnerable to predatory species that can detect 
this light (Jägerbrand and Spoelstra, 2023). In addition, 

58

in protected areas and areas with rare protected red-
light  sensitive  species,  for  example  lesser  horseshoe 
bats, even red light should be used with caution, and 
where possible no lighting should be the default. 

Further  interdisciplinary  research  is  required  in  the 
future on lit areas, such as roadways, and pavements, 
where  light  is  required  to  enable  human  access  in 
these  areas,  whilst  minimising  ecological  impacts. 
An  EU  workshop  on  light  pollution  in  autumn  2022, 
suggested piloting projects in sensitive areas to identify 
least  environmentally  harmful  lighting  to  achieve 
this  goal  amongst  Member  States  (Council  of  the 
European Union, 2022). As part of this evaluation more 
information is needed on other environmental stressors 
that  could  affect  light  pollution,  and  particularly  its 
interplay  with  other  pollutants  (Widmer  et  al.,  2022). 
The interaction of light pollution with other pollutants is 
still poorly understood, and therefore a growing concern 
of the science community. Researchers have developed 
a practical method to record the size, composition and 
distribution of aerosol particles through satellite imagery 
(Kocifaj & Barentine, 2021), enabling an assessment of 
how air pollution interplays with light pollution. This has 
shown that reducing air pollution, specifically aerosols, 
decreases  night-sky  brightness  by  tens  of  percent  at 
relatively small distances from light sources. 

Alongside pollution other global change drivers, such as 
climate change or land-use change, can interact with 
the effects of ALAN (Rillig et al., 2019), which could be 
additive (the sum of the impacts is equal to each impact 
added together), antagonistic (cumulative effect that is 
less than additive) or synergistic, whereby cumulatively 
effects of sum of stressors is more than the additive 
effect  (Birk  et  al.,  2020).  One  example  is  night-time 
warming that combines with light pollution and has non-
additive  impacts  on  predator–prey  interactions  (Miller 
et al., 2017). Researchers are developing novel ways to 
disentangle  these  effects  on  biodiversity  and  provide 
insight into how approaches could be put into practice 
to potentially tackle more than one environmental issue 
(Widmer et al., 2022). For example, Wilson et al. (2021) 
used  a  large  data  set  generated  by  community  and 
citizen scientists to analyse effects of ALAN and noise 
pollution  on  bird  occurrences.  This  showed  a  number 
of informative insights, such as that species occupying 

closed  habitat16  were  less  tolerant  of  both  sensory 
stressors compared to those occupying open habitat. 

largescale 

interdisciplinary 

This complexity of interactions in light pollution and its 
impact, further emphasises the need for interdisciplinary 
research  that  can  consider  different  aspects  of  light 
at night time, its interaction with other environmental 
stressors,  and  its  multiple  impact  (Spoelstra  et  al., 
2021).  Two 
research 
projects investigating the impact of light pollution and 
effectiveness  of  mitigation  measures,  are  planned  to 
be  funded  within  the  Horizon  Europe  Research  and 
Innovation  Programme  (HORIZON-CL6-2023-BIODIV-
01-2)17.  Both  projects  will  investigate  light  and  noise 
pollution  with  respect  to  impacts  on  biodiversity  and 
ecosystem services and innovative mitigation measures, 
with  ‘AquaPlan’  (101135471),  focussed  on  European 
seas lakes and rivers, whereas ‘Plan B’ (101135308) is 
focussed on terrestrial ecosystems.

Lampyris  noctiluca,  Female  common  glow  worm  of  Europe, 
displaying  to  attract  a  male,  Germany.  Source:  Photo  by 
Wofl~commonswiki CC BY-SA 2.0 DE
https://commons.wikimedia.org/wiki/File:Lampyris_noctiluca.jpg

16  Closed habitat species live in areas with vegetation cover such as forest. Open habitats have less canopy/vegetation cover, such 

as grassland.

17  Biodiversity and ecosystem services (HORIZON-CL6-2023-BIODIV-01)

 
 
59

4.3.  Species for which the impact of ALAN is not known

Research is emerging on the impact of ALAN on the 
only migratory insect species listed by the Convention 
on  Migratory  Species  (CMS),  the  Monarch  butterfly, 
Danaus  plexippus.  This  study  indicates  that  ALAN  is 
likely  impacting  the  internal  circadian  clock  of  this 
daytime active butterfly species, causing them to fly at 
night if subjected to artificial light, potentially impacting 
their migratory behaviour (Parlin, Stratton and Guerra, 
2022). The process when Monarch butterflies emerge 
from  their  chrysalises  is  also  controlled  by  a  light-
triggered  circadian  clock,  therefore,  constant  light 
from ALAN could also disrupt this. Further research on 
the  impact  of  exposure  of  artificial  light  at  night  on 
this well-known American butterfly species is required. 

The  sensitivity  of  different  taxonomic  groups  to 
different spectra of light is an area which requires 
more  attention.  Hölker  et  al.  (2021)  note  that 
many species of aquatic turtles, and fish are more 
sensitive to longer wavelength in freshwaters (i.e. 
red  light)  and  to  shorter  wavelengths  in  marine 
environments  (i.e.  blue  light).  It  cannot  then  be 
assumed that all turtle species are most sensitive 
to  shorter  wavelengths  –  the  case  with  marine 
turtles – as freshwater species of fish and turtles 
may be more sensitive to red light, due to how light 
is filtered by salty water (where red light does not 
penetrate  far  due  to  the  salt  content)  compared 
with freshwater (Hölker et al., 2021).

The  European  glow  worm,  Lampyris  noctiluca, 
and  the  rarer  Phosphaenus  hemipterus,  is  a  non-
migratory  European  species  impacted  by  ALAN. 
Despite  ALAN  impacting  the  behaviour  of  these 
charismatic  bioluminescent  species  in  Europe, 
there are few studies on how this is affecting their 
abundance,  and  distribution  (Owens  et  al.,  2022). 
However,  some  recent  studies  demonstrate  that 
some of these bioluminescent animals can discern 
between different colours of light, even at low light 
intensities, and respond to changes in intensity of 
LED lights (Booth et al., 2004; Van den Broeck, et 
al.,  2021).  Clearly  further  research  is  required  to 
elucidate the impact ALAN might have given these 
emerging findings in this group.

There is a lack of information regarding how ALAN 
impacts  the  majority  of  migratory  species.  No 
studies  were  found  for  any  CMS-listed  mammals 
(apart  from  bats),  crocodiles  or  Chondrichthyes 
(sharks, and rays) with the latter being notably at 
risk  in  the  Mediterranean  Sea,  where  more  than 
50%  of  species  are  listed  as  at  risk  of  extinction 
(Serena et al., 2020). There is a limited amount of 
information  available  about  some  migratory  fish, 
including the CMS-listed European eel, which raise 
concerns – but further research may be necessary 
before action can be taken. Whereas the impact of 
artificial  light  on  marine  turtles  has  been  studied 
extensively,  there  is  a  knowledge  gap  when  it 
comes to non-marine turtles (Perry et al., 2008). 

There  is  little  research  on  the  impact  of  ALAN 
on  two  groups  of  marine  turtle  populations  – 
Kemp’s Ridley turtle (Lepidochelys kempii) and the 
upper  Amazonian  population  of  the  Arrau  turtle 
(Podocnemis  expansa).  The  Kemp’s  Ridley  turtle 
is listed as critically endangered by the IUCN and 
found  in  European  waters,  with  a  French  study 
from 2021 investigating stranding events, bycatch 
and cold stunned turtles in the Bay of Biscay area 
– noting that further research was needed into the 
environmental drivers leading to these occurrences 
(Chambault et al., 2021).

Many  bird  species  have  been  shown  to  be 
vulnerable  to  light  pollution,  but  there  are  also 
calls  in  the  literature  for  more  research.  Many  of 
the  bird  species  listed  on  the  CMS  do  not  belong 
to  the  orders  or  families  which  are  covered  by 
the current guidelines. How the prey of migratory 
species  is  affected  by  ALAN  also  needs  to  be 
studied  further,  for  example  future  research  into 
the impacts of ALAN on moths (which are prey for 
many  other  species)  needs  to  consider  for  all  life 
stages, rather than only focusing on adult moths, 
as well as looking at more moth species (Boyes et 
al., 2021).

 
60

4.4.  Marine and Freshwater habitats lacking ALAN data

More than 50% of the world's population live within 
a  distance  of  3  km  (Kummu,  et  al.,  2011)  from 
water, and there are many current and future shifts 
that may increase ALAN in marine areas, such as 
night-time  fishing  and  floating  cities  (Herbert-
Read et al., 2022). However, whilst information on 
the  extent  and  the  amount  of  ALAN  potentially 
affecting water bodies is in its infancy, ecological 
studies assessing the impact of artificial light that 
penetrates  into  the  ocean  on  marine  organisms 
is  even  scarcer  (Smyth  et  al.,  2021;  Jechow  and 
Hölker, 2019a). 

Aquatic  habitats  need  protection  from  ALAN 
and  they  are  vulnerable,  as  aquatic  organisms 
are  adapted  to  low  light  conditions  and  these 
environments  are  largely  open  spaces,  with  few 
barriers  to  prevent  light  penetration.  With  the 
extreme  light  sensitivity  of  aquatic  habitats,  the 
precautionary principle should be applied in most 
cases,  perhaps  following  the  lead  from  France, 
where  light  on  water  surfaces  is  forbidden  by 
law.  As  with  all  situations  discussed  previously, 
the  default  should  always  be  no  artificial  lighting 
in  or  near  an  aquatic  habitat.  Where  lighting  is 
unavoidable for human safety, for example, on an 
oil rig or boat, the light should be restricted to the 
lowest  intensity  required,  shielded,  be  used  on  a 
timer  and  in  an  appropriate  colour  spectrum  to 
minimise impact on aquatic organisms.

There is little guidance on addressing the impacts 
of ALAN and management of lighting in the marine 
environment,  although  there  is  research  and 
suggestions  around  the  use  of  artificial  lighting 
in commercial fishing (Nguyen and Winger, 2019). 
Sport  fishing,  also  known  as  recreational  fishing, 
sometimes  uses  artificial  light  at  night  to  attract 
fish  to  the  boats  (see  figure  20).  However,  this 
practice  has  an  impact  on  non-target  species  in 
the  aquatic  environments,  and  potentially  on 
migratory  seabirds.  The  approach  to  regulating 

this  multi-billion-dollar  hobby  differs  between 
different  worldwide  jurisdictions  –  with  some 
banning recreational night fishing entirely (Greece), 
while  others  restrict  the  use  of  artificial  light  in 
night  fishing  (Spain)  (Pawson  et  al.,  2008;  Cooke 
et al., 2017). The Convention on Migratory Species 
suggests  a  case-by-case  approach  to  assessing, 
managing  and  mitigating  ALAN 
(see  2.4.6) 
(Marangoni et al., 2022; Nunny, 2021). Monitoring 
of  night  light  in  marine  and  coastal  areas  is 
improving,  and  studies  are  able  to  use  modelling 
techniques to estimate the level of night light on 
the seafloor (Davies et al., 2020). Further research 
to  establish  the  thresholds  for  ecological  and 
environmental  impacts  in  marine  and  freshwater 
habitats is warranted, focusing on indicator species 
that are most likely impacted.  

At present there are very few studies on the impact 
of using tuneable LEDs to mitigate ALAN in marine 
ecosystems.  Tim  Smyth,  et  al.  (2020),  however, 
suggest  that  their  research  in  the  Tamar  estuary 
offers a compelling case for using artificial red light 
in costal installations to reduce exposure in marine 
habitats, as it attenuates faster and is less visible 
to  marine  animals.  The  application  of  red  light  in 
marine  environments  to  mitigate  the  impacts  of 
ALAN  is  likely  to  be  favourable  (ibid.),  however,  a 
number  of  marine  organisms  are  also  negatively 
affected by amber and red light. As such, retrofitting 
red light filters to existing luminaires, or switching 
to long length lights is likely to improve potential 
ALAN impacts on most marine organisms, but will 
not completely eradicate the impacts altogether. 

Despite a lack of data in marine areas, Marangoni 
et.al.  (2022)  offer  ten  golden  rules  for  mitigating 
the  impact  of  ALAN  in  marine  habitats  –  citing 
existing data on the impacts of ALAN in the ocean, 
and applying the precautionary principle (see figure 
19 below). 

61

Figure 19.  Ten golden rules for dark night conservation for marine habitats. Source: © 2022 The Authors. Global 
Change Biology published by John Wiley & Sons Ltd – available and downloaded via Creative Commons licence

62

Figure 20: (a) Different marine environments not affected by Artificial Light Pollution at Night (ALAN), and (b) 
marine environments under the potential impacts of ALAN: (i) Sandy beaches effects on invertebrate species 
day-night activity rhythms and biodiversity, effects in the on-beach orientation of adults and hatchling turtles, 
and seabirds fledgling grounded by ALAN; (ii) Rocky intertidal shores – influence in metabolic activity/behavior 
of primary producers, sessile and mobile animals; (iii) Shallow water coral reefs – effects on gametogenesis and 
the synchronization of gamete release in prominent coral species, and negative impacts over fish reproduction, 
(iv)  Pelagic  environment  –  inhibition  of  vertically  migrating  zooplankton,  and  disorientation  and  mortality  of 
seabirds. Source: © 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd – available and 
downloaded via Creative Commons licence.

However, there is a paucity of data on freshwater 
systems: they have not been studied with satellite 
data due to their relatively small area (Jechow and 
Hölker, 2019a), and the most widespread method 
to  measure  ALAN  in  freshwater  uses  simple 
handheld  luxmeters  above  the  water  surface. 

Few  citizen  science  studies  have  been  developed 
to  describe  nocturnal  artificial  light  conditions  of 
aquatic systems. 

63

As well as being an issue on land, light pollution impacts the marine 
environment particularly those areas with intensive offshore development 
and coastal urbanization. An area of 1.9 million km2 of the world’s 
coastal seas are exposed to ALAN at a depth of 1m (equivalent to 3.1% of 
the global exclusive economic zones).

Source: Smyth et al., 2021.

Very low light levels that artificial light generates are critically important 
to biological organisms, … But how much of an impact it has in the marine 
environment has been pretty understudied.

Source: Tim Smyth, lead author and oceanographer, ‘global atlas of artificial light in the sea’. 

In  addition  to  overcoming  these  challenges  there 
is  a  need  to  consider  the  different  forms  of 
light  pollution  for  different  types  of  water.  Blue 
wavelengths  are  transmitted  to  greater  depths 
in  the  ocean,  as  water  molecules  absorb  the 

longer  wavelengths.  In  contrast,  coastal  waters 
and  freshwater  systems  typically  absorb  longer 
wavelengths and are more variable in their inherent 
optical properties (Kühne et al., 2021).

4.5  Geographical disparities in impacts of ALAN

There are many regions and countries that will be 
more  affected  by  light  pollution  in  the  future,  but 
which  currently  have  a  low  level  of  awareness  of 
the  problem.  For  example,  residential  lighting  is 
becoming more possible in developing countries as 
technology is accelerating accessible and affordable 
lighting, particularly from renewable sources. 

Although accessibility to lighting has been hindered 
by  the  pandemic  it  seems  it  is  likely  to  increase 
again  (International  Energy  Agency  (IEA),  2022). 
This is a welcome development, but also one that 
will increase light pollution in these countries. For 
example,  researchers  have  recently  highlighted 

light pollution as an emerging issue in India with a 
survey on awareness showing that 57% of Indian 
people  surveyed  were  unaware  of  the  term  ‘light 
pollution’ (Kaushik et al., 2022).

Within  Europe,  the  northern  European  Member 
States  have  longer  nights  and  are  more  densely 
populated,  so  it  may  be  that  ALAN  has  more  of 
an  impact  in  these  areas.  However,  some  of  the 
southern  Member  States  may  have  more  night-
time migratory bird species. Further elucidation on 
the  geographical  disparity  of  ALAN’s  impacts  on 
the environment could aid creation of appropriate 
local guidelines.

Expressing concern over satellite data showing that global light pollution 
has increased by at least 49% over the 25 years to 2017, and that there 
are hardly any areas with complete night darkness left in Europe

International Workshop - ‘Light Pollution 2022;’ note from Czech Presidency.

 
64

5.  Summary and conclusions

Artificial light at night is an emerging environmental 
threat,  with  a  growing  research  field  which  has 
produced hundreds of articles in the last five years. 
Some  progress  has  been  made  in  understanding 
aspects  of  the  harm  that  exposure  of  artificial 
light  at  night  can  cause 
the  environment, 
including  sensitive  habitats,  vulnerable  night-
time active taxa and, of course, humans. However, 
understanding how to mitigate the environmental 
impacts of ALAN is complex, and there is no single 
solution for all scenarios, because organisms have 
different visual systems, and a diversity of ways to 
responding to light.

Yet solutions are emerging, and case studies now 
abound  on  different  types  of  mitigation  measure 
which limit the negative impact of ALAN in different 
situations. These include technical aspects of lights, 
such as shielding, dimming and timers, as well as 
the  impacts  of  different  colour  spectra.  The  ideal 
solution  of  course  is  not  to  use  artificial  light  at 
night at all, and keep naturally dark areas dark, to 
protect species present in these habitats. However, 
when  lighting  is  needed  for  human  activity  in  an 
outdoor  space,  then  the  least  amount  of  light 
required  should  be  used  –  lighting  only  the  area 
needed, with the minimal amount of light required 
to ensure visibility for the user. In identifying where 
these  areas  of  lighting  are  justified,  depends  on 
the  context;  however,  for  road  traffic  lighting  the 
Swedish Transport Association case study, detailed 
in Box 7, offers a best practice approach.

is 

important  also 

to  dispel  a  common 
It 
misconception,  by  clarifying  that  an  area  with 
brighter artificial light at night is not always safer. If 
lighting is poorly designed, unshielded and glaring, 
it  can  cause  temporary  blindness  in  a  person, 
making  it  more  difficult  to  identify  objects  and 
potential threats, and for human eyes to adjust to 
see clearly the low contrast surroundings. Accepting 
that dimmer well-placed lighting can be safer and, 
therefore,  preferable  to  poorly  designed  brighter 
lighting  would  enable  lower  ALAN  in  human-
inhabited areas, benefitting biodiversity and human 
health (Zielinska-Dabkowska, et al., 2023). 

Where and when ALAN is unavoidable, using low light 
intensity, warmer light spectra, such as amber and 
red, although not a perfect solution, is less harmful 
overall  than  higher  intensity,  or  blue  spectra  LED 
lighting.  However,  it  is  worth  noting  that  reducing 
artificial light – both its extent and its duration – is 
more beneficial overall. So, it may be useful, in some 
situations,  to  retrofit  dimmable,  warmer  spectra 
LEDs that are shielded and on a timer.

There  are  a  myriad  of  other  management  and 
technological  measures  to  mitigate  the  impacts 
of  ALAN,  with  some  examples  discussed  in  this 
brief already, which can be combined and tailored 
according to the needs of a particular area. Some 
of these measures include adaptive street lighting, 
buffer zones around dark reserves, dark corridors 
–  connecting  dark 
infrastructure  –  buildings 
designed  to  reduce  light  spill  and  reflection  on 
glass,  and  dense  vegetation  to  hinder  light  spill. 
It is clear that more research is needed to monitor 
the  effectiveness  of  these  mitigation  measures, 
singly  and  in  combination,  at  protecting  the  vast 
array  of  wonderful  night-time  active  species  we 
have in Europe, such as the lesser horseshoe bat, 
European glow worm and loggerhead turtles, from 
the negative effects of ALAN. 

There  are  a  number  of  policy  barriers  that  have 
prevented  widespread  uptake  of  the  mitigation 
measures  discussed  in  this  brief.  Most  lack  of 
uptake is due to this being an emerging field, where 
many mitigation strategies may only have one or 
two  case  studies  relevant  to  a  particular  species 
or  context.  The  establishment  of  standardised 
thresholds  and  guidelines  is  emerging,  and  so 
uniformity  across  the  European  Member  States 
(MS) is presently lacking, however, some examples 
of  local  authorities  and  MSs  good  practice  from 
within this brief could be useful in this regard. 

Reassuringly,  it  is  within  our  power  to  reduce  the 
environmental harm caused by artificial light at night, 
often simply by switching off the lights. This is exactly 
what some cities have begun to do due to the energy 
crisis, by instigating lighting curfews. These money-
saving  steps  by  local  governments  also  benefit 
biodiversity,  for  example  reducing  the  impacts  of 
skyglow on migratory birds or turtle hatchlings.

65

Outdoor  lighting  is  not  currently  included  in  the 
2030  Agenda  for  Sustainable  Development, 
adopted  by  all  members  to  the  United  Nations, 
although most of the 17 sustainable development 
goals  are  impacted  by  light  pollution.  To  ensure 
a  more  ecological  sustainable  future  in  Europe, 
and  globally,  individuals,  cities,  governments  and 
international  conservation  organisations  need  to 
include  the  effects  of  anthropogenic  lighting  in 
planning and decision-making. 

Light  pollution  has  historically  been  perceived 
as  less  of  a  priority  issue  than  some  other 
environmental  stressors,  and  so  there  is  less 
awareness  amongst  the  media,  and  the  public  of 
this issue, and the wide-ranging environmental and 
human health impacts this may have. However, a 
growing  field  of  research  demonstrating  ALAN’s 
negative  impacts,  alongside  knowledge  of  some 
quite  simple  measures  that  can  mitigate  these, 
are leading to this issue gaining more widespread 
light-pollution 
political  attention.  With  many 
reduction strategies also lowering energy use, and 
potential costs to local authorities – this could be 
an area where gains could be made on all fronts by 
some carefully selected measures. 

66

Box 15: Actions to mitigate ALAN in homes, businesses and through 
Green Public Procurement  

Wildlife  species  are  more  sensitive  to  light  than 
humans, with artificial light at night disrupting the 
nocturnal  behaviour  of  many  species,  including 
pollinators such as nocturnal moths, thus impacting 
the  successful  pollination  of  plants.  As  this  topic 
is  gaining  increasing  attention  with  regards  to 
Green  Public  Procurement,18  recommendations 
were developed for road lighting and traffic signals 
(Wilk, Rebollo and Hanania, 2019):

 y Use  of  lighting  products  compatible  with 
dimming  controls  that  limit  upward  light, 
blue light emissions and switch off lighting in 
closed parks;

 y limit  illumination  to  desired  areas  such  as 

sidewalks or roads; 

 y dim  light  sources  to  the  lowest  acceptable  

light intensity; 

 y reduce the number of light fixtures installed in 

and around ecologically vulnerable areas; 

 y shield path lights in green spaces from the top 
and  the  bottom  to  minimise  their  impact  on 
nearby biodiversity; 

 y install temporal limits – motion activation and/
or automatic timers that extinguish lights when 
not  needed,  or  when  vulnerable  species  are 
likely to be most affected, i.e. during the two-
month  long  courtship  season  of  the  common 
glow-worm (firefly); 

 y use 

red  wavelength  LED 

lights,  adjust 
wavelength  to  red  and  exclude  blue  and 
ultraviolet spectrum. 

What we can all do in our homes: 

To lower skyglow in your city, town or village you can 
minimise light pollution outside your house, in your 
garden, terrace or front door. Do you need lights in 
these spaces all the time? If not, can they be used 
only at certain times of night? Motion activation or 
temporal lighting with automatic timers can help. 
Extinguish  lights  when  not  needed,  or  dim  to  the 
lowest acceptable light intensity. Use lights which 
are  shielded  –  so  light  doesn’t  travel  upwards  or 

downwards  unnecessarily,  and  use  warm  lights 
with  a  red  wavelength  rather  than  a  blue  one. 
Lastly, simply close your curtains or shutters in the 
evening when you turn on lights inside your home 
(IEEP, 2020).

Businesses:

Dark sky standard for domestic and non-domestic 
lighting  was  developed  by  the  United  Kingdom 
Dark  Skies  Partnership  (UKDSP),  a  collaborative 
forum  of  the  Commission  for  Dark  Skies,  the 
Countryside Charity (CPRE), the Institute of Lighting 
Professionals and the Society of Light and Lighting. 
The  aim  of  UKDSP  is  to  improve  sky  quality  by 
reducing ALAN via education, effective behavioural 
change  and  promotion  of  environmentally-
sensitive lighting (UKDSP, 2021):

 y Using automated blackout blinds and shutters 
at  night  –  a  relatively  low-cost  and  effective 
option for eliminating internal light spill without 
impacting on internal spaces; 

 y timers  on  blinds  should  be  set  for  within  one 

hour after sunset; 

 y they can be used either in the design phase, or 

post installation; 

 y break up continuous glazing by removal or use 
of  external  shutters  and  shields  to  keep  the 
overall  glazed  area  to  less  than  50%  of  the 
total elevation area; 

 y glazing should not exceed 25% of the floor area 
to meet energy efficiency building regulations 
(which  does  depend  on  thermal  properties  of 
the glass); 

 y turn off internal lights when not needed or at 

close of business;

 y any commercial greenhouse should have zero 

light spill. 

18  Technical report “Revision of the EU Green Public Procurement Criteria for Road Lighting and traffic signals” which proposes 

concrete G-index values (directly related to blue light content) for parks, gardens and ecologically sensitive areas.

67

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GETTING IN TOUCH WITH THE EU

In person
All over the European Union there are hundreds of Europe Direct centres. You can find the address of the 
centre nearest you online (european-union.europa.eu/contact-eu/meet-us_en).

On the phone or in writing
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FINDING INFORMATION ABOUT THE EU

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website (european-union.europa.eu).

EU publications
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EU law and related documents
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EU open data
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These  can  be  downloaded  and  reused  for  free,  for  both  commercial  and  non-commercial  purposes.  
The portal also provides access to a wealth of datasets from European countries.

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