Outdoor Lighting and Crime - Amper

• spatial extent also ranging from small areas to national scales,
• dark or dim durations from a single night to thousands of nights,
• historical data extending to over a century, and
• lighting industry literature and standards, published and ad hoc outdoor photometry,
appearance of outdoor lighting at night, anecdotal evidence and measures of visibility
of celestial objects, skyglow measures and photographs, and satellite-derived measures
of upward light emissions.
A negative correlation between lighting and crime, long claimed by Situational Crime
Prevention practitioners and others, appears to be an unwarranted intuitive extension of the
lighting and fear of crime relationship to actual crime. No reliable evidence for this negative
general relationship has been found. ‘Dose-response’ curves are known from experiments
about fear of crime. Fear tends to diminish with increasing light, so the curves typically have
negative gradients (eg Boyce et al. 2000, Fig. 7). Specific curves for lighting and actual crime
are unknown but typical net effects tend to have positive gradients. Whatever residual
experimental evidence there might be for a non-zero inhibiting effect of lighting on crime, it
appears to be overwhelmed by the collective evidence for the opposite effect. 43
The issue of whether lighting is an active causal factor, or is merely a co-variant of something
else such as population density, may usefully be studied within a theoretical framework. This
framework is now developed around the evidence already established, mindful of the
difficulties of working with field data that are much more open to confounding than data
collected in controlled experiments. In addition, while correlation is a necessary but not
sufficient condition for making confident inferences about causality, it does not matter which
statistical technique has been used to establish correlation (eg Wuensch 2001).
4.4 LIGHTING AND CRIME HYPOTHESIS
4.4.1 Possible processes and causality
Proponents of lighting for crime prevention assume or believe that lighting at night will
reduce crime. Published results of quasi-experiments sometimes indicate this effect,
sometimes no effect and occasionally even an increase in crime. The question examined has
usually been ‘Does lighting reliably reduce crime or have no effect?’ Clearly a more general
form would be ‘Does lighting reliably affect crime or not, and if it does, in which direction is
the effect and how big is it?’ But even this ignores at least three other possibilities. Firstly,
the relationship between lighting and crime could be chaotic in the mathematical sense. 44 If
so, it would be possible for conventional before-after testing at various times and places to
produce statistically significant results in both directions of effect. Although a chaotic
association is a possibility, it seems unlikely considering the consistently positive associations
found in temporal and spatial data. It is not the simplest available explanation of the observed
facts and is therefore disregarded here.
43
Further evidence to support this statement is given in following sections.
44
It is sometimes popularly called the ‘butterfly effect’, an allusion to the extreme sensitivity
of chaotic systems to initial conditions.
46