Outdoor Lighting and Crime - Amper

level will be linked to clock time (including variations such as daylight saving time) and the
seasons.
Social factors such as time of day outside of school hours (NCJRS 1999) and work hours are
known to play a large part in the incidence of crime, as described in Part 1 and Section 1.2
above. Large fluctuations in the rate for many types of crime occur consistently at fixed clock
times, usually without any definite or consistent link to specific light levels. To single out any
specific effects of light changes, at sunset or sunrise for example, crime would be better
plotted against phase of day and night rather than against clock time.
Lunar phase and meteorological factors such as cloud and fog can have a profound effect on
the light level at a given day/night phase, however, so it would be better again to plot crime
against measured light level. Nobody appears to have pursued this so far, which sits strangely
against the vast amounts of government, corporate and domestic expenditure on artificial light
at night as a supposed crime-prevention measure. As an example from highly developed
countries, the contrast with requirements for evidence-based official approval of
pharmaceuticals is extreme.
Even when daylight saving time is not in use, the use of clock time or even local solar time as
a proxy for ambient light levels over night and day results in the integration of any crime
effects of light level over light stimulus values varying in some cases from the assumed mean
by ten times (1 log unit) or more in each direction. Unless the observations and analyses
involved can be conducted in more than two dimensions, the cost of avoiding this reduction of
apparent effect of light would be to integrate the other effects instead, over a substantial and
frequently ill-defined range. In terms of the effects on a light and crime graph, this would
effectively ‘smear out’ fixed-time-of-day crime effects along the light axis, thereby increasing
the prospect of being able to identify crime effects attributable to absolute or relative light
levels.
4.2.2.2 Possible forms of crime and lighting curve
Curve C in Figure 6 is representative of the form of variation of crime with ambient light
implied by conventional Situational Crime Prevention theory. Its form, let alone its possible
partition into light-dependent and other parts, appears to be ignored in the literature. The
observational evidence supporting a curve of this form is that aggregate crime in some
countries (eg the UK) is greater at night than by day. However, it is often overlooked that
clock time rather than light level appears to be the main factor governing night or day
prevalence in some cases. 40 As the ambient light is increased artificially or increases naturally
from night conditions, separately or together through twilight values, by definition the crime
rate indicated by the curve must reduce down to the daylight level, whatever that may be in
absolute terms.
Although the Curve C shown is notional, the vertical scale shown is realistic to the extent that
the net excess, integrated over the range of light levels experienced at night, is at most a small
40 For example, drink-spiking and brawls are commonly associated with nightclubs and bars
at night, but armed robberies of banks appear to be rare at night because not many banks are
open then.
40