Outdoor Lighting and Crime - Amper

Curve E is the simplest form of variation that is consistent with the low crime values observed
in outdoor lighting blackouts (or, more accurately in terms of residual light levels, as
‘dimouts’). By itself, outdoor darkness could hardly be expected to stop crime such as fraud,
Internet offences, dangerous driving, or domestic violence, so the overall rate would not drop
to zero. In the absence of any evidence to the contrary, the ‘true’ curve must nevertheless
start low down at the dark end of the illuminance axis. Then it must rise monotonically to
asymptote to the daylight crime level, like Curve E.
4.2.2.3 The general form of lighting and crime curve
If there is a true form of the variation of crime with lighting, then it should be consistent with
all observations. According to Curve E, crime increases with increased light up to daylight
levels of crime and light. If light levels and not social circumstances determine crime levels
at night, then it could be expected that the numbers of crimes at night would always be less
than the numbers of crimes by day. Because education, work and community service
activities are predominantly in daylight hours, however, it could be expected that there would
be more potential criminals at leisure and available to commit crime in the evening.
Likewise, there may be more potential victims out and about after the end of school hours and
work hours for the day. Reports of the proportions of crime by day and night generally do not
include details of such factors. In this case, the known social factor of leisure time is expected
to act in the direction of increasing the percentage of crime that occurs at night.
As mentioned in Section 1.2 above, some reports show a night excess of crime, and others, a
daytime excess. Figure 5 shows both: for many years in the USA, there has been a greater
percentage of residential burglary by day than at night, while it is the other way around for
non-residential burglary. This is clear evidence against a single ‘true form’. ‘General form’
or ‘net form’ would be better, especially if crimes aggregated across types have to be
considered in preliminary work. The net result from Figure 5 is that a greater percentage of
all burglaries take place in daylight, so a general curve for burglaries would have to show a
net reduction of burglaries at night in comparison with burglaries by day.
The actual number of burglaries in the USA has been declining for many years. This does not
invalidate the observation (Figure 3) that outdoor artificial light and overall crime are growing
together, especially given that increased police numbers and increased incarceration have
been acting to reduce crime, as mentioned in Sections 2.3.3 and 2.4.
Because there are substantial fluctuations in the crime rate observed wholly within bright or
dim light conditions, day or night, some unknown part of any general changes in crime
indicated by Figure 6 will be a result of whatever social factors apply in particular cases. The
available evidence supports the presence of substantial effects both from light and social
factors. Because of the time delays associated with some of the social effects (which would
include the social changes responsible for the indirect effects of light), all of the possible
forms of curve in Figure 6 would be best regarded as representing equilibrium states rather
than short-term effects.
The available evidence certainly appears to favour Curve E over Curve C or Line D,
especially at low light levels. The case is far from conclusive for higher light levels, however.
The general form might be a mixture of any two of these forms of variation, or even all three,
depending on the mix of crime, social influences, and the balance of beneficial and adverse
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