Outdoor Lighting and Crime - Amper

multiple of the day rate. In Figure 6, the excess over the day rate is arbitrarily set at a factor
of 4 for 0.0001 lux, an illuminance that is near-blackness in terms of visual appearance.
Curve C is monotonic (ie having a slope that does not change sign), the simplest plausible
form of variation.
A problem with Curve C is that there appears to be no reliable evidence to back up the belief
of at least some Situational Crime Prevention people in a tendency for rampant lawlessness
and anarchy in near-darkness. In fact, as the ambient light becomes too dim for any visual
response, the crime rate could be expected to level off as shown by the dashed alternative
dim-light end for Curve C, or even to drop, instead of continuing to rise steeply. This logical
need for an asymptotic or non-monotonic dark characteristic does not appear to have been
considered by theorists to date.
The form of curve for fear of crime found by Boyce, Eklund, Hamilton and Bruno (2000) is
rather like Curve C, having a high value in dim light and dropping down towards the daylight
value as illuminance increases. The Boyce et al. results only extend down to about 0.1 lux so
the flattening off that could also be expected for the fear of crime curve at very low light
levels does not appear in their graph. Nevertheless, the form of Curve C illustrates the
popular notion that actual crime increases with reducing light. This belief might be based on
common experience that the fear of crime tends to increase with reducing light at night,
together with failure to distinguish adequately between fear of crime and actual crime.
Curve C illustrates an important point discussed at length in Part 1. If this curve does truly
represent the actual situation, it indicates that a typical lighting treatment of about 3.375 times
increase in ambient light at night (or 0.53 log unit) would produce a rather small reduction in
crime. For Curve C as drawn and the lighting increment B as shown, the reduction is about
9% in crime, ie from its initial value, x, to 0.91x. Crime reductions claimed in some
experiments in the UK have been as much as this value compounded fourteen times.
As an example of an excessive claim, Farrington and Welsh (2002a,b) calculated the daytime
indoor crime reduction was to 1/3.82, or 26%, in the Birmingham market hall relighting of
Poyner and Webb (1997). Suppose that the market hall with its original lighting had twice the
crime rate that it would have in full daylight. The crime reduction claimed for increasing the
light by some unknown amount (Poyner and Webb did not give a numerical factor for the
light increase) is so great that crime must have been reduced to about half of the daylight
value, an illogical result. Another possibility is that the original crime rate was four times the
daytime rate, and really intense relighting changed near darkness to daylight levels. However,
the writer is not aware of any reports of such high rates being observed anywhere as an
identifiable consequence of dim lighting.
Line D in Figure 6 represents the case where crime is completely independent of ambient
light, and all non-lighting effects balance out. This is a possibility indicated by experiments
in which the null hypothesis (viz, that light has no effect) is not disproved. It would also be
indicated by a meta-analysis cross-product ratio that was not reliably different from zero. To
date, typical lighting treatments have usually been such a small part of the daylight-todarkness
range that it would be a large extrapolation to claim light-independence over this
whole range.
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