Version of 2002-11-26
B. A. J. CLARK1
Astronomical Society of Victoria, Inc., Australia
Scientific studies support common experience that light tends to allay the fear of crime at night. It is widely believed that outdoor lighting also helps prevent actual crime at night, but experiments have given equivocal results. Thorough scientific reviews published in 1977 and 1997 concluded that the effects were unknown. Recent work in the UK suggests that lighting does have a crime reducing effect by day as well as at night. This work appears to be flawed in ways that favour a crime-reducing result. While it seems reasonable to expect that social effects of outdoor lighting at night might have some influence on daytime crime, so far there appears to be no reliable evidence for any net crime-preventing effect, day or night. It even appears possible that lighting might increase crime, a topic investigated in Part 2 of this work.
CCTV competes with outdoor lighting for crime-prevention funding. The available evidence indicates that CCTV is not an effective alternative. Until the lighting and crime issue is better understood, no more security lighting or other lighting for crime-prevention should be installed and the funding should be redirected to rectification of existing overbright and glary outdoor lighting.
© Copyright B. A. J. Clark, Australia 2002
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(original file LP040.DOC, typesetting made from its LATEX version)
It is common experience that artificial light at night tends to allay the fear of crime, and this has been confirmed by scientific studies. It is also commonly believed that outdoor lighting helps to prevent crime at night but the evidence is equivocal. Crime-reducing, nil, uncertain, and increasing effects have variously been reported for relatively short-term field studies of lighting and actual crime. Thorough scientific reviews published in 1977 and 1997 in the USA concluded that the effects of lighting on crime were unknown. Claims that more outdoor artificial light reliably reduces crime largely originate from a relatively small number of experiments in the UK. Government authorities there and elsewhere have been increasingly inclined to install more and brighter lighting as a supposed crime prevention measure. Street crime in the UK rose by 28% in the year ending April 2002. Consistent with this, it now it seems that the experimental and analytical results in question are unreliable.
Some researchers claim that increased lighting at night can bring about social changes that influence crime by day as well as at night. Others deny this. In principle, the issue can be tested by making a distinction between direct effects, which are immediate, and indirect effects, which generally take time to develop. Lighting is defined as having a direct effect on crime if the light physically aids or hinders criminal acts at night. Indirect effects presumably depend on intervening social processes. Their development time results in the possibility for indirect effects to act by day as well as at night.
Some existing accounts of lighting and crime experiments present only nighttime crime data but this is no guarantee that the effects claimed are only direct. Other experiments produce day and night data, separately or combined. Direct and indirect effects often appear to be mixed indiscriminately in analyses of changes accompanying the lighting treatment. This could explain some of the discrepant results reported.
Another source of difficulty is that field experiments tend to be set up on an opportunistic basis, utilising municipal relighting programs determined by local authorities. Brighter lighting often appears to be installed as a response to localised crime concentrations. Over time, crime in these `hotspots' tends to regress naturally to the mean, encouraging the erroneous conclusion that the lighting treatment has had a beneficial effect. This reinforces the use of lighting for crime prevention, regardless of the facts.
Researchers have been cautioned over the years to describe the photometric changes of the lighting treatments in detail. This has typically been ignored, leading to imprecision in results. A worse outcome is that researchers have seemingly been unaware when the results claimed have been improbably large for the lighting increments involved.
Attempts to define a precise relationship between typical lighting increments and measures of crime changes by pooling available results may actually mislead. The apparently improved precision of the weighted average generally does not compensate for systematic bias towards a beneficial effect that appears to be common to many of the individual experiments. Some of this bias is likely to be an outcome of the common practice of experiments being funded by stakeholder organisations.
On the basis of the studies reviewed, no reliable effect can be claimed for outdoor lighting increments as a means of preventing or reducing actual crime. It is possible that lighting could even be counterproductive, a topic taken up in Part 2 of this work. Governments should ensure that resources are not wasted by the installation of any more security lighting or other outdoor lighting at all where the justification includes or implies crime prevention. National lighting standards should not contain any statement or implication that outdoor lighting will prevent or deter crime.
The evidence is examined for the effectiveness of CCTV as an alternative to lighting for crime prevention. As with lighting experiments, CCTV field studies have typically been done with inadequate attention to the photometric situation at night. If there are any non-zero effects of lighting on crime, lighting changes introduced for the cameras or for other reasons and ignored by the experimenters may have confounded the results. The best available estimate of the effect of CCTV as a crime deterrent is only 4%, and even that may be an overestimate. Funds earmarked for crime-prevention lighting should not be diverted to new CCTV installations, but used instead for rectification of existing overbright and glary lighting.
The original version of this document and its companion Part 2 was a public submission in May 2000 to a parliamentary committee on drugs and crime in the state of Victoria, Australia. It drew attention to the uncertain effects of outdoor lighting on crime. It was then recast as general guidance on outdoor lighting and crime within Australia, and posted on the website of the Astronomical Society of Victoria. This led to postings on several overseas websites. The need to expand the work into two parts only became apparent during a revision that started in January 2002.
This part deals with existing experimental and analytical work on outdoor lighting for crime prevention. Part 2 presents evidence that growth in crime is linked to growth in outdoor ambient artificial light.
Some references to Australian Standards and local lighting issues have been retained as illustrating general problems. The Australian spelling conventions used tend to follow UK practice, but quotations retain the original forms. Dates are given in the format recommended by the International Standards Organisation (ISO 2014-1976).
Revised versions of this document may be issued without notice as new information becomes available. Readers are advised to check the facts for themselves and to seek independent expert advice before taking any actions that could adversely affect visibility, safety, commerce or insurance cover, or might increase vulnerability to crime.