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Common experience, confirmed by experiments, is that artificial light at night tends to allay the fear of crime. Any deterrent effect on actual crime is difficult to investigate with field studies, partly because of pervasive extraneous influences. Crime-reducing, nil, uncertain, and crime-increasing effects of light at night have variously been reported for night or day or both, separately or combined or both. Thorough scientific reviews published in 1977 and 1997 in the USA concluded that the effect of lighting on actual crime was unknown. Nevertheless, crime prevention practitioners there and elsewhere, and even some academics, have asserted for decades that lighting is an important weapon, or even the most important weapon, in the fight against crime. UK work published since 1997 has increased academic acceptance that crime prevention effects of lighting do apply in some circumstances, although this UK work has been criticised by others for its procedural and analytical shortcomings.
New terminology is defined to improve understanding of existing outdoor lighting and crime studies and to assist the formulation of new studies:
Direct effects of light may aid or hinder criminal acts at night, at the time of actual or intended commission.
Indirect effects of light act through intervening social factors, generally with time delays, and may influence crime by day as well as at night.
Conflict of interest is a serious current problem in scientific work. The bias it leads to in results has long been known but its extent has only become apparent in recent years through the excess of results favouring stakeholder sponsors in medical and pharmaceutical trials. Lack of due disinterest of researchers in the findings tends to bias results. Bias from non-financial conflicts of interest is also recognised as a substantial problem. It diminishes the likelihood of reporting and publication of null results or results that are counter to expectations. Bias therefore has to be suspected in lighting and crime studies that were partly or fully supported by lighting-related interests or performed by researchers including one or more having an undue desire for a particular result.
Evidence of bias was found in some of the papers reviewed, manifested as one or more of inappropriate emphasis on why lighting should or even would reduce crime, or failure to search for, mention, discuss or otherwise give due weight to contrary views and facts. In general, conflicts of interest can be expected to bias crime prevention studies to favour beneficial effects of lighting.
Where separate scientific experiments give differing results for a particular quantity, the mean of pooled results generally provides a more accurate estimate. A formal review and meta-analysis can usually do even better by rejecting poorly conducted experiments and weighting the results of those remaining. A recent review and meta-analysis of lighting and crime studies examined was found to include an indiscriminate mix of direct and indirect effects. The meta-analysis result derived for a typical relighting treatment is impracticably beneficial. This follows from the several successive treatments that would be possible in practice, thereby allowing compounded reductions in crime well beyond anything likely on present indications. This error appears to have arisen because of inadequate photometric quantification of lighting treatment, contrary to warnings in the 1977 and 1997 reviews mentioned in Section 9.1 above.
Of the 13 studies included in the meta-analysis, serious procedural or analytical shortcomings or both were found in at least five of them. Photometric aspects are inadequately presented in all of these five studies also. A consequence is that researchers failed to recognise when systematic and other errors led to false or overlarge beneficial effects. Removal of suspect studies from the meta-analysis brings the weighted average result much closer to a null effect. Forcing the upper limit for the 95% confidence interval to have a realistic value leads to a null result if all studies are included. It appears that a counterproductive effect of lighting on crime would emerge from discarding the five problematical studies and applying corrections for the various forms of bias thought likely to have acted in some or all of the remaining studies.
The best that can be concluded at this stage is that there appears to be no compelling evidence for any appreciable net direct beneficial effect of increased outdoor lighting in reducing actual crime at night or for net indirect beneficial effects by night or day. National lighting standards should not state or imply that outdoor lighting has any value for crime prevention or deterrence.
To the extent that outdoor lighting is intended to prevent crime, its capital and operating costs appear to be a waste of public and private funds. It may even be counterproductive. In the case of industrial and commercial infrastructure, the cost burden reduces industrial competitiveness and hinders economic growth.
News media have uncritically perpetuated the myth of increased lighting for crime prevention. Journalists and others concerned need to check the facts more carefully. An extensive pro-lighting campaign started in the 1990s appears to have swayed many UK authorities to install brighter outdoor lighting as a supposed crime reduction measure. The UK Crime and Disorder Act 1998 may have accelerated this process. In the year ending April 2002, street crime in the UK was reported as having increased by 28 %, quite inconsistent with the claimed crime-prevention effect of lighting.
Closed-circuit television (CCTV) competes with lighting for available crime-prevention funds. A recent meta-analysis of CCTV intervention studies indicated that the effect was a mere 4% reduction in crime. However, even this meagre result may be unreliable or erroneous because of extraneous confounding factors in real-world experiments. Funding saved by stopping expenditure on more and brighter lighting for crime prevention should not be diverted to CCTV.
The lighting and crime issue needs to be better understood. The issue is addressed in Part 2 of this work. Meanwhile, governments should ensure that resources are not wasted by the installation of any more security lighting at all, and that no street lighting or other public lighting extensions or upgrades are agreed where the justification includes or implies crime prevention. Funding earmarked for crime-prevention lighting should be redirected to rectification of existing overbright and glary outdoor lighting.