Outdoor Lighting and Crime - Amper

Marchant (2003) pointed out that the quantity called the odds ratio by Farrington and Welsh
would be more correctly described as a cross-product ratio (CPR). He also showed that
incorrect statistical treatment by Farrington and Welsh resulted in values of the CPR that were
too large and confidence intervals that were too narrow. As with the errors described in Part
1, the net effect is to increase the likelihood that the true value of the CPR is less than 1. Such
a value would mean that crime increases with the amount of outdoor light, consistent with the
observations described above. 38
The idea that outdoor crime at night has a net positive direct connection with outdoor light
levels may seem counter-intuitive, given the common experience that lighting tends to allay
the fear of crime. If true, it would imply a predominance of daytime crime over night crime,
as actually happens with residential burglaries in the USA. Research would be required to
establish the relative contributions of light and social factors in determining such
predominances, but some general observations are possible here.
If all crime did decrease steeply without temporal displacement as a direct effect of increased
lighting, and if night and day opportunities for crime were equal, turning night into day with
artificial light could be expected to do no more than halve the overall crime rate. But some
crimes are generally committed indoors (eg ‘white-collar’ crime). Any direct facilitating
influence of outdoor lighting at night on such crimes does not seem credible. Therefore, for
all kinds of crime aggregated, the maximum possible decrease accompanying the installation
of intense outdoor lighting, according to existing belief, would appear to be limited to less
than a factor of two.
Ambient outdoor light levels at night in many parts of even the world’s most brightly lit cities
are still well short of daylight values in general. The actual crime rate increases shown in
Figures 1, 2, 3 and 4 generally well exceed a factor of two over two decades or so. A positive
(adverse) direct effect of lighting on crime is in accordance with the long-term direction of
change in observed crime but the national increases in crime rate appear too large to be
accounted for by direct effects of lighting increases. The crime-changing effects of lighting
claimed by Painter and Farrington (1997, 1999a,b) do include what are here called indirect
effects and could account for the magnitude of the observed changes, except that they are
clearly in the wrong direction. Any direct effects of lighting on crime appear to be swamped
by other processes.
Excluding temporal displacement, a direct daytime effect on crime, increase or decrease, by
what some commentators have called ‘switched-off outdoor lighting’ can hardly be regarded
as anything but unlikely if not far-fetched. Nevertheless, there are known environmental and
socio-economic effects on crime incidence, such as seasonal effects (Baumer and Wright 39
1996, Jochelson 1997, DCPC 2001) or, say, the effects of wars or overseas financial changes
on international tourist numbers and hence numbers of tourists available to be crime victims.
These fit the above definition of indirect effects. Indirect social or economic effects of
38 In Section 5.5.2 of Part 1, the reciprocal of the ‘odds ratio’ was proposed as a more useful
measure called the ‘crime ratio’ or similar. Crime increase with added light would thus give a
crime ratio of more than 1.
39 Baumer and Wright cited 36 references on the seasonal variation of crime in refuting a
claim by Farrell and Pease (1994) that there was almost no published work on the subject.
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