Outdoor Lighting and Crime - Amper

markedly greater if there is substantial cloud cover. Normally this ‘free’ addition to outdoor
lighting could be thought beneficial, insofar as it tends to lighten dark shadows and make
seeing a little easier. But darkness appears to be beneficial in crime prevention, so that
increased ambient illumination from light pollution, especially with cloud cover, could be
quite undesirable. This would be a new reason for limiting upward light spill from all light
sources in a town or city. If the outdoor lighting system is designed with minimal spill and
glare for good performance in overcast conditions, it will still be good in clear conditions.
US states that have already replaced their old streetlights with full-cutoff types (eg
Connecticut) or are in the process of doing so (eg Illinois) may have a better outcome than
they might have bargained for.
7.2.3 Crime, vegetation and lighting
Kuo and Sullivan (2001) examined crime rates within 98 apartment buildings of a public
housing estate in Chicago. The surroundings of the buildings ranged from mostly canopy
trees and grass, through small trees, some grass and some paving, to predominantly paved
areas. There were few shrubs. Both violent crime and property crime were reliably lower for
‘greener’ apartments. This relationship held after accounting for factors such as building
heights, number of apartments, and occupancy rates. Levels of nearby vegetation explained
7% to 8% of the variance in the number of crimes reported per building. The effect was
suggested to be a combination of vegetation increasing informal surveillance and vegetation
mitigating some of the psychological precursors to violence.
Kuo and Sullivan contrasted the result with the common belief that vegetation facilitates
crime because it hides perpetrators and criminal activity from view. 92 There is apparently no
quasi-experimental evidence to support this belief, only anecdotes from park managers, police
and car burglars. Vegetation is neither necessary nor sufficient for a crime to take place.
Indeed, trees and grass in outdoor spaces of public housing actually inhibit graffiti, vandalism
and littering. There is good evidence that the presence of visibly dense vegetation does
increase fear, including fear of crime, with limitation of view distance as an important factor,
although one study showed that the sense of safety increased with the density of trees in an
inner-city courtyard.
All of this forms something of a parallel with existing beliefs and facts about lighting, fear of
crime and actual crime. There is actually a connection, in that there are causal interactions in
both directions between light and vegetation. Particularly in the case of canopy trees, the
underlying area is subject to shading of natural and artificial light sources. City outdoor lights
cause increased growth of foliage on nearby tree branches (Casagrande and Giulini 2000,
Roman, Cinzano, Giacometti and Giulini 2000), which increases the amount and annual
duration of shading from these branches. Figure 1 in Kuo and Sullivan (2000) shows
extensive shadowing from the estate canopy trees in June. Their Figure 2 shows that the
canopy was continuous in some areas. At least in the part of the year when leaves were
present on the trees, the areas with trees could have had as little as say one-tenth as much
ground-level illuminance as the treeless areas, night and day. From the present results, the
92 This belief is widely propagated as fact by governments, police, crime prevention
practitioners and civil groups, as an Internet search will quickly show.
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