Select Committee on Science and Technology Seventh Report


The extent and nature of light pollution

The properties of light

The joint Countryside Commission and Department of the Environment's Guidance Lighting in the Countryside: Towards Good Practice (1997), describes the properties of light as:

"Light is a type of radiation and forms part of the electromagnetic spectrum visible to the eye. It is measured in lumens (lm). A modern electric light takes in energy in watts, and its efficiency can be measured in lumens per watt (lm/w). The amount of light falling on a surface is know as the illuminance and is measured in lumens per square metre or lux. This is easy to calculate and measure and is therefore widely used. The illuminance of direct sunlight is approximately one hundred thousand lux, but normal daylight, which is filtered through a cloudy sky is between five thousand and ten thousand lux, while moonlight is as little as 0.25 lux.

Luminance, or brightness […] is directional and is measured in candelas per square metre (cd/m2).

The other term commonly used by lighting engineers is luminous intensity. This refers to the strength of light in a given direction and is measured in candelas (cd). However, in reality, a source's luminous intensity is seen by the eye relative to the brightness of its surroundings, and this is not easy to measure."

What is light pollution?

42. It is generally acknowledged that there are three types of light pollution: sky glow, which has principally contributed to professional astronomy being undertaken abroad; glare, and light trespass which have the most adverse effect on the amateur and professional astronomers based in the UK. However, there is no legal or official definition of "light pollution". The Government's guidance Lighting in the Countryside Towards Good Practice (1997), a joint Countryside Commission and Department of the Environment publication, described light pollution as a "very general term which refers to effect of over-lighting resulting from poorly designed lighting schemes and excessive levels of light.[71] The guidance was produced as a response to the concerns raised in the 1995 White Paper: Rural England - A Nation Committed to A Living Countryside which stated that the intrusiveness of lighting in the countryside should be kept to a minimum. Lighting in the Countryside sought to mitigate "excessive" "unnecessary" and "obtrusive" lighting. The Institution of Lighting Engineers (ILE) said in its memorandum "lighting in itself is not a problem; it only becomes a problem where it is excessive, poorly designed, badly installed or poorly maintained."[72] The issue is not aided by the uncertainty over which Government department has lead responsibility for the problem of light pollution. Several departments are involved: Transport (street lighting is a main cause of light pollution), DEFRA (the Department has published the main government guidance on the matter and would implement a statutory nuisance on light) and ODPM (planning is currently the only control over lighting).


43. Sky glow is the orange glow seen over towns and cities. It is caused by light travelling through the atmosphere being refracted or scattered by water droplets or particles (aerosols) caused by dust, pollen, bacteria, spores, salt from sea spray, mineral particles lifted from deserts and waste products from industry. It is therefore worse in heavily polluted areas, and will always exist to some extent when the air quality is poor. The glow over urban areas is not always localised and can be seen from many miles around, often spreading into dark rural areas. This brightness of the sky obscures distant stars, especially those low in the sky or just above the horizon, making them invisible to the naked eye.[73]

44. The orange colour of the glow is due to low-pressure sodium street lighting units that were the most common type of lighting installed in the past.[74] The light is radiated directly upwards from the light fitting (luminaire) and light is also reflected back off whatever is being lit - the road, pavement, or building etc.[75] Even lighting traversing a path at a shallow level above horizontal level will cause sky glow as the light shining will be refracted against particles and droplets in the atmosphere. An element of sky glow is also attributable to radiation from celestial sources and luminescent processes in the Earth's upper atmosphere.[76]


45. "Glare" consists of light shining into the eye, preventing the person from seeing the illuminated scene properly - for example a car with headlights on full beam will dazzle a driver or pedestrian moving the other way. Similarly, an over-powerful security light or floodlighting will dazzle and cause a temporary, sometimes painful contraction of the muscles controlling the iris, making it difficult to see into the areas surrounding the light. The effect can cause momentary blindness and bring safety risks for drivers moving rapidly from dark areas to relatively bright ones.[77]


46. Light trespass is defined as light that shines from one property into another where it is not wanted. It is also referred to as "light spill". Security lights are the most common culprit.

47. The Department for the Environment, Food and Rural Affairs is currently considering the responses to its consultation "Living Places - Powers, Rights, Responsibilities". This consultation paper was published at the same time as the Office of the Deputy Prime Minister published "Living Places: Cleaner, Safer, Greener".[78] The DEFRA consultation sought opinions on how council powers could be revised to manage public spaces. This included whether new regulations for the positioning of external lighting (other than street lights) and powers to extend the statutory nuisance regime to include lighting were necessary.[79]

Who and what does light pollution affect?


48. Our inquiry has concentrated on astronomy. Light pollution has forced astronomers to move to areas with dark skies,[80] or to travel great distances to find dark areas, or to be content with a severely reduced number of stars visible. Skyglow, light trespass and glare have all contributed to light pollution. The reduction of stars visible affects the observations of amateurs, professionals, students and pupils of astronomy in the UK: only a privileged few will have the advantage or opportunity of accessing an overseas world-class telescope first hand.

49. The majority of the evidence we received was from astronomers who regularly observed from their own back gardens. They explained their frustration at having observing conditions ruined by a neighbour's security lights or from glare from streetlights and floodlights. Observatories also complained of the effect of this localised light pollution. The Rt. Hon. Keith Hill, MP, Minister of State, Housing and Planning, Office of the Deputy Prime Minister, told us "I am permanently blasted out of my chair in my conservatory by the totally inexplicable but extremely effective security light which a neighbour has across our back garden fence."[81] In spite of his first hand experience of the unpleasantness of light trespass, Mr Hill's understanding of the nature of light pollution is flawed. He told us "We are talking about different issues when it comes to light as a nuisance from the issue of light pollution in general."[82] The remedies for the different types of light pollution may differ, but light trespass, glare and sky glow are all caused by an unnecessary misuse of light. This confusion is indicative of the Government's disjointed treatment of the problem of light pollution.

50. Whilst there are different types of light pollution and different ways to tackle them, the problem for each type of light pollution is the same: inappropriateness of the direction and power of light. Astronomers in particular are affected by all three types of light pollution: the majority of the population, be they the general public, school pupils, postgraduates, professional or amateur astronomers, are prevented from seeing the night sky in its entirety by light pollution. We hope that this Report will inform the Office of the Deputy Prime Minister of the effects of light pollution on astronomy.


51. The loss of the dark night sky and stars has been noticed by ordinary citizens who wish to be able to see the stars, without the orange glow. The BAA conducted a survey in 1991 which concluded that more than 90% of those who wished to see the night sky were prevented in doing so to some extent by light pollution.[83] We received evidence from members of the public who are not astronomers, and yet have suffered a great deal from the nuisance caused by inappropriate floodlighting and over-powerful industrial or domestic security lighting.[84] Security lighting shining through windows and curtains can cause great distress and have adverse effects on health and well being by disturbing sleep patterns and causing stress. A 1993 survey by the Chartered Institute of Environmental Health indicated that 80% of local authorities had received complaints about light pollution. When a similar survey was conducted in 1996 the level of complaints was found to have risen by 44%. The main sources of complaints were domestic security lighting (55%), sports facilities (21%) and industrial and commercial premises (19%).[85]


52. Lighting in the Countryside discussed the effects of light pollution on wildlife, and concluded that there could be adverse ecological effects on:

    "The attraction of birds to lights has been known for a long time. A close correlation has been demonstrated between commencement of dawn singing in thrushes and critical light intensity at sunrise, suggesting that artificial lighting may modify the timing of natural behaviour patterns. Reproduction in birds is photoperiodically controlled, and artificial increase of day length can induce hormonal, physiological and behavioural changes, initiating breeding. Around sixty species of wild birds have been brought into breeding condition prematurely by exposure to artificially long days in winter. In addition, bright lights such as those on telecommunication towers, lighthouses and other tall structures may attract and disorientate birds, especially on moonless nights, resulting in mortalities. Nocturnal species, many of which are already under threat, are particularly likely to be disturbed by the presence of bright illumination."[89]

53. We were told that the Empire State Building turns its lights off once a year to prevent the deaths of migrating birds.[90] We have not looked in detail at the environmental impact of light pollution but the action we recommend later in the report would have significant beneficial effects on many aspects of the natural environment.


54. The Committee has received evidence on the significant amount of energy wastage that occurs from inappropriate lighting. Examples include: all night (and sometimes daytime) floodlighting of buildings, all night and over-powerful domestic security lighting, the lighting of empty car parks, as well as inefficient street lighting which throws light upwards into the sky rather than downwards onto the road or pavement it is supposed to illuminate. There is no doubt that the production of electricity using fossil fuels causes continued pollution of the atmosphere, which in turn creates greater sky glow.

55. Following the Kyoto Protocol of 1997, the UK's target for the reduction of greenhouse gases (including CO2) was a 12.5% decrease in 1990 levels by 2010. In our Report Towards a non-carbon fuel economy: research, development and demonstration, we concluded that this target was unachievable if current policies and market conditions remained in place.[91] Both the Performance and Innovation Unit Report The Energy Review, and the Energy Research Review Group recommended that energy efficiency had a vital role to play in reducing the UK's carbon emissions. The PIU called for a 20% improvement in domestic energy efficiency by 2010.[92]The Energy White Paper said that improving energy efficiency is "the cheapest, cleanest and safest way of addressing our energy policy objectives."[93] Reducing the amount of electricity used to provide safe and effective levels of lighting for homes, streets and public buildings must be a priority for the Government.

56. We deal later with how much energy could be saved if unnecessary lighting were switched off and street lighting changed.

57. The adverse effects of light pollution on energy consumption are both undisputed and a source of much disquiet and annoyance for large parts of the population. The Government fails to take the issue seriously and does not consider light pollution in its full context - with its effect on everyone.

Evidence of deterioration

Anecdotal evidence from astronomers

58. We have received many memoranda from professional and amateur astronomers around the country giving anecdotal evidence of the steady increase in light pollution. Most individuals had been observing between twenty and fifty years and described the decreasing visibility of stars over the years as disastrous, particularly since the 1960s. This decade coincides with the installation of street lighting consisting of low-pressure sodium lights, high pressure mercury or tungsten light sources which are difficult to control optically, resulting in unacceptable high levels of light pollution.[94] The increase in levels of air pollution and the decrease in air quality in general will have also exacerbated skyglow.

59. Astronomers measure the brightness of stars in stellar magnitudes. This is a logarithmic scale reflecting the way the eye reacts to light. The scale runs from negative to positive, with the brightest stars having magnitude -1.[95] A star of +6 magnitude will be one hundred times fainter than a star of magnitude +1. The brightest star in the night sky is Sirius, which is of -1.4 magnitude. [96] In a pristine clear night sky, from a dark site, stars of the sixth magnitude should be visible with the naked eye: one should be able to see the Milky Way and Andromeda Spiral Galaxy.[97] However, due to urban skyglow, only stars brighter than the +1 magnitude are visible in urban areas, and there are only sixteen stars in the whole sky brighter than +1 magnitude.[98] The Milky Way is no longer visible once the faintest star visible is of magnitude +4.[99]

60. The following table shows the number of stars that should be visible in one third of the total night sky, per limiting magnitude (or faintest star visible).

Limiting Magnitude
Number of Stars visible

Source: IDA

61. Star maps, showing which stars are visible in the various magnitudes, can be found in the written evidence.[100] The following data is taken from evidence submitted by astronomers; showing how light pollution has affected observations various parts of the country:

  • Forty years ago the Milky Way was visible from Liverpool; now only stars of the third magnitude are visible.[101]
  • Thirty years ago, the Milky Way was visible in Finchley; now only stars of the third magnitude are visible.[102]
  • In 1976 it was possible to see the Milky Way regularly from Bexleyheath; now it is only visible on a very few nights a year.[103]
  • Twenty five years ago, the Milky Way was visible from Bristol.[104]
  • Only stars of the fifth magnitude are now visible in Maidenhead.[105]
  • Only stars of the fourth magnitude are now visible in Darlington.[106]
  • In the 1950's stars of the sixth magnitude were visible in Brightlingsea, Essex; now only third magnitude is visible.[107]
  • In Berkshire, in the 1960's sixth magnitude stars were visible; in the 1970's 5.5 magnitude; and in the 1980's and 1990's stars of the fifth magnitude were visible.[108]
  • In the late 1980's it was still possible to see the Milky Way in South East England; now it is impossible.[109]

62. Additionally, in response to our call for evidence, the Society for Popular Astronomy (SPA) held a survey amongst its members, 800 of whom responded. Included in the findings were:

  • Nearly 80% could not see the Milky Way or could only see it on the best nights.
  • had to travel between 5 and 50 miles to find acceptable viewing conditions.
  • in 8 had to travel over 50 miles.[110]


63. The Campaign for Dark Skies (CfDS) is a section of the British Astronomical Association (BAA). It was created in 1990 by a group of astronomers "concerned about the erosion of the night sky by uncontrolled and ill directed lights of all kinds."[111] They wish to see the right amount of light and only where needed. The Campaign to Protect Rural England (CPRE) considers that the dark sky is one of the things which had defined the countryside. In 1994 CPRE and BAA had jointly produced a leaflet called Starry Starry Night, which tackled light pollution.

64. Following the receipt of pictures from the weather satellites owned by the US Air Force, the two organisations joined up again to produce Night Blight!, a campaign against light pollution. These two organisations should be commended for their work in bringing light pollution to the attention of the wider public. Scientists at the US National Oceanographic and Atmospheric Administration (NOAA) used the Operational Line Scanners aboard the weather satellites to measure the total brightness of artificial night time lights within small areas of the Earth's surface. Night Blight states "These maps provide an approximate but adequate overall measure of light pollution in each locality".[112] NOAA had been creating these maps since 1993, and so CPRE were able to compare the maps from 1993 and 2000. Whilst some areas had become darker (2%), the majority of the UK had become more brightly lit, with fewer areas of truly dark sky. CPRE banded the areas of lightness into colours, with navy being the darkest areas, and red being the brightest. In England, the darkest band fell from 15% in 1993 to 11% in 2000, whilst 26% had shifted up a brightness band between 1993 and 2000.[113]

65. Night Blight states that one's view on the ground will depend on whether there are any local bright lights to impede your view of the night sky. However, on a clear night, it should be possible to see the Milky Way in a deep blue banded area - but no chance of seeing the Milky Way on even the clearest night within the red and yellow bands where most of the population lives.[114] CPRE and CfDS believe that these pictures prove the major growth in light pollution in recent years. Other satellite pictures have also been produced showing images of the light output of countries around the world, e.g. by Professor Woody Sullivan, Astronomy Department of the University of Washington.

66. When faced with the satellite pictures, the Rt. Hon. Keith Hill MP said: "in terms of light pollution, my own impression is that a certain amount of progress is being made. If you look at these dramatic satellite pictures of the expansion of areas, it seems to me that it is, as we say in the trade - us New Labour types, do we not? - a matter of the red light joining up in the urban and suburban partnership, spreading over into rural areas".[115] The thrust of the Minister's argument seemed to be that as urban areas had borne the brunt of the increase in light pollution, the satellite pictures were not to be regarded as an indication that light pollution was getting worse.

67. It is reassuring that Lord Rooker, Minister of State for Regeneration and Regional Development, ODPM, during a debate on light pollution in the House of Lords on 19 June 2003, stated on the subject of the satellite pictures: "There has been an increase in light pollution: there is no question about that. The issue is what we do about it […] we need positive solutions to the issue […] There is a lot to do, as the recent satellite photographs show. There is no question about that."[116] We are disappointed by the inconsistent approach by the Government on the issue of light pollution. We hope that the more realistic attitude adopted by Lord Rooker is the true reflection of the Government's approach. The Government should not dismiss the compelling evidence of the satellite images of the United Kingdom, which clearly show an increase in light pollution in both rural and urban areas.

Not just a UK problem

68. After the Netherlands, the UK is the most light polluted country in Europe. Light pollution is a global problem. Astronomers worldwide have raised concerns over the impact of light pollution. The International Dark Skies Association was set up in the USA in 1988 to tackle light pollution. It now has over ten thousand members in many countries.[117] To date, together with the UK and the USA, there are organisations in the following countries who are working to counter the effect of light pollution: Australia; Belgium; Canada; Denmark; Finland; France; Germany; Greece; Italy; Japan; Malta; Slovenia; South Africa; and Switzerland.[118] The International Astronomical Union (IAU) has passed resolutions at eight general assemblies on the issues of light pollution. In 1999, the IAU and the United Nations Special Environment Symposium "Preserving the Astronomical Sky" made recommendations to member states.[119] In September 2002, the Second European Symposium on the Protection of the Night Sky took place in Lucerne, Switzerland.

69. Should the Government decide to take action against light pollution, it would not be the first government to do so. The following countries, states, regions or cities have enacted legislation to control light pollution: the Czech Republic; Lombardy, Italy; Catalonia, Spain; Canary Islands, Spain; Maine, USA; Arizona, USA; Bisei, Japan; and Calgary, Canada. It is clear that some Governments are taking the threat of light pollution, to both the astronomer, the ordinary citizen, and the environment, seriously. Details of how each country or region controls light pollution can be found in an annex to this Report. [120]

70. Those who have spent a lifetime studying the night sky have charted its deterioration and have now joined forces with environmental campaigners, astronomers in other countries, and also with those members of the general public, increasing in numbers, who have experienced the adverse effects of the increasingly badly lit environment. We are in no doubt that light pollution is getting worse. We recommend that the Government acknowledge this fact and give a commitment to taking serious action to tackle this problem, as other governments have proved it is possible to do.

71   Department of Environment and Countryside Commission, Lighting in the Countryside: towards good practice, 1997,p 17 Back

72   Ev 185 Back

73   Ev 181 Back

74   Ev 224 Back

75   Ev 181 Back

76   International Commission for Illumination, Guide on the limitation of the effects of obtrusive light from outdoor lighting installations, CIE 150: 2003, p 2 Back

77   Lighting in the Countryside, p 20 Back

78   Eleventh Report of the Office of the Deputy Prime Minister: Housing, Planning, Local Government and Regions Committee, Session 2002-03, Living places: cleaner, safer, greener, HC 673-I. Back

79   Ev 222 and ODPM Committee, Living Places: cleaner, safer, greener. Back

80   Ev 66, 153 Back

81   Q 164 Back

82   Q 164 Back

83   Ev 110 Back

84   Ev 55, 61, 62, 214 Back

85   Lighting in the Countryside, p 20 Back

86   Lighting in the Countryside, p 22 Back

87   CIE 150:2003, p 6 Back

88   CIE 150:2003, p 6 Back

89   Lighting in the Countryside, p 23 Back

90   Ev 119 Back

91   Fourth Report of the Science and Technology Committee, Session 2002-03, Towards a non-carbon fuel economy: research, development and demonstration, HC 55, para 216 Back

92   Performance and Innovation Unit, The Energy Review, February 2002, paras 9.12, 7.63 Back

93   Department of Trade and Industry, Our energy future- creating a low carbon future, Cm 5761, February 2003, para 3.47 Back

94   Ev 53, 182 Back

95   Ev 179 Back

96   The scale continues as follows: a star of +5 magnitude is 2.512 times brighter (2.512 being the fifth root of 100) than a star of magnitude +6, and so on. Light Pollution, Responses and Remedies, p 23 Back

97   Ev 47 Back

98   Ev 179 Back

99   Light Pollution, Responses and Remedies p 34 Back

100   Ev 206 Back

101   Ev 158 Back

102   Ev 67 Back

103   Ev 64 Back

104   Ev 63 Back

105   Ev 79 Back

106   Ev 83 Back

107   Ev 99 Back

108   Ev 112 Back

109   Ev 213 Back

110   Ev 160 Back

111   Ev 47 Back

112   Campaign to Protect Rural England and the British Astronomical Association, Night Blight!, 2003 Back

113   Night Blight!, p 7 Back

114   Night Blight!, p 7 Back

115   Q 155 Back

116   HL Debate 19 June 2003, col. 954 Back

117   Ev 41 Back

118   See Light Pollution, Responses and Remedies for details, p 169. Back

119   Ev 175 Back

120   See Annex 1. Back

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