Outdoor Lighting and Crime - Amper

educed light at night could have been partly or completely responsible for the reduction in
recorded crime.
Before wholesale inner-city tree-planting schemes are introduced to reduce crime, it would
appear useful to do photometric surveys of the estate at night, with and without moonlight,
and with and without dense cloud cover, to estimate the mean annual illuminances at night in
the vegetated areas. The observed crime rates could then be tested for correlations with these
illuminances. Reducing outdoor ambient light at night might prove to be more effective than
planting trees.
7.3 LIGHTING AND ROAD ACCIDENTS
Traffic safety people often express a desire for more street lighting as an accident
countermeasure. Present lighting levels and length of coverage are largely limited by capital
and running costs, most of which are funded from government revenue. The case for street
lighting has often been bolstered by claims that it adds security, but it appears that the claims
are merely emotive rather than quantitative. The existing situation is that calls to reduce street
lighting might be regarded as foolish or worse, although reduction has actually happened for
budgetary reasons in Calgary and some Massachusetts towns, as mentioned. The issue now
becomes of pressing importance because street lighting is a major source of outdoor artificial
light at night.
Are the traffic safety people right? Their belief in the value of more light does have a
respectable basis in that visual performance at night is lower than by day, and it generally
improves with increased artificial lighting, even when accompanied by glare from semi-cutoff
luminaires. Furthermore, the International Commission on Illumination (CIE) has examined
the problem and pronounced that street lighting is an accident countermeasure (CIE 1992,
Fisher 1993). Reasons for this are:
• The rate and severity of traffic accidents at night are reliably greater than by day.
• Visual performance degradation by low light levels is considered to be the main
reason. 93
• Statistically significant reductions in traffic accidents at night usually occur after street
lighting is installed or increased.
• In round figures, up to a third of the accidents at night on unlit roads are considered to
have been avoidable by the installation of street lighting.
This would appear to put the issue beyond contention. But the issue is not straightforward.
Brighter lighting has been known to encourage drivers to travel faster. There are also some
parallels with the lighting and crime situation. Firstly, there are non-light-related differences
between day and night. In the driving case, these include practices that could also have some
tangible adverse effect on driver performance, eg people appear more likely to consume
alcoholic drinks after the end of their daytime work, in the evening and at night. Conditions
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Reaction times certainly increase in dim light (Clark 1995, Plainis, Murray, Chauhan and
Charman 2002).
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