outdoor lighting and crime, part 1 - Astronomical Society of Victoria

EXECUTIVE SUMMARY
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.
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