Outdoor Lighting and Crime - Amper

effects of light, direct and indirect, in aiding and hindering crime. Instead of a single curve,
the reality could be an area between or covering the curves, perhaps wider in some parts than
in others.
Another possibility is that the general curve might not be monotonic. It would still need to
start low down in accordance with available evidence, but may cross the axis and asymptote
down to the daylight crime rate at higher light levels much as Curve C does. This is Curve F
in Figure 6. Increasing light at night would therefore have an undesirable effect on crime up
to the light level corresponding to the peak of this Curve F. At and near the peak, small
lighting changes would have little effect. At higher light levels along Curve F, increased
lighting would have a small beneficial effect on crime, ie a reduction. Overall, however, there
would still be a net adverse effect of increasing illumination artificially above natural night
levels. An attraction of Curve F is that it might help to explain the ‘mixed’ results of some
lighting and crime quasi-experiments to date, instead of supposing that they are entirely a
result of confounding by unknown real-world factors.
A further possibility that could explain mixed results is based on Curve E. This form would
not be a single line but a band representing the crime variation that undoubtedly occurs in the
real world at specific light levels. This band could be thought of as representing the range of
variation within statistical confidence limits. At this stage, not much can be said about the
likely vertical extent of what could conveniently be called Band E (not shown in Figure 6 to
avoid excessive detail), except that it may be bounded on its lower side by zero crime, at least
at the dim light end, implying a Poissonian distribution. The upper part of Band E may well
extend above the daylight crime line at any light level but would seem more likely to do so as
it approaches daytime light levels.
At daytime light levels, Band E is constrained to coincide with the level of variation applying
to crime in daylight. In this diagram, the band will have a much smaller vertical extent
because it is integrated over daytime hours as a consequence of the definition of the daytime
baseline. Band E, low down and broad at low light levels, therefore converges by definition
to a thin horizontal band at high light levels. At below-daylight levels, Band E could readily
extend above the horizontal line marking the daylight level, accounting for the existence of
elevated levels of some crimes in some places at night. The mean or perhaps the geometric or
logarithmic mean of the vertical extent of Band E would be marked by Curve E.
4.2.2.4 Linking theory and observation
The daylight end of Curve E is fixed. The low light end is in general accordance with
observations of low crime rates in near-dark conditions. If the direct effect of light in
increasing crime were the sole mechanism acting, the whole curve would be fixed. However,
the indirect effect of light is not only present but appears to predominate, at least over the
illuminance range indicated by Line A. Its effect is to change crime through some social
action, generally with an associated time delay. The present meagre evidence indicates that
the net indirect effect of increasing light at night is to increase crime by day and night more or
less equally. A change in light at night would therefore result in some change in the absolute
level of crime by day, in due course.
In deriving the overall result of a lighting change on crime (indirect plus direct effects),
account would need to be taken of the relative change in crime at night over the duration of
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