Outdoor Lighting and Crime - Amper

that major cross streets occur at intervals ranging from about 80 to 90 in street numbers, and
gaps generally occur in the street number sequences at these intersections. While undesirable,
the two-year time delay between the drugs crime data and the photometric data does not
appear to be sufficient to invalidate the test. This is based on the evidence of relative stability
in the patterns of arrest locations over the previous five years, as shown in DCPC (2001).
Crime and lighting plots for each street were done both with the mean illuminances and with a
logarithmic transformation of these means. As mentioned in Section 2.4, logarithmic
transformations are often justified in researching visual effects. The crime and lighting
association is shown equally well by the linear and log plots in the case of Russell Street. For
Bourke Street, the vertical scale had to be smaller for the linear graph because of the high
peak value. This tended to obscure details that were already difficult to see in the plotted
curve near illumination minima. The logarithmic transformation was selected for Figures 15
and 16 because it shows the lighting and crime relationship better in the case of Figure 15.
The logarithmic scale reduces the peaks and accentuates the variations at the dim end. Here,
the graphs have the same vertical scale, facilitating comparison.
The figures indicate that drugs crime arrests take place away from places with artificial
illumination extremes, especially minima, notwithstanding the likelihood that some
proportion of the arrests shown took place in the daytime. 78 That proportion has apparently
not been made public by the police. The use of horizontal plane illuminance seems to
accentuate the peaks and troughs more than was apparent in the appearance of faces at the
time of the measurements. Semi-cylindrical illuminance 79 might have been a better measure,
but it is more time consuming to ascertain and did not appear warranted in this exploratory
work. 80 Several of the illuminance minima were at street intersections because of interruption
measurement. The block end measurements were made close to the intersection of the
footpath midlines at each corner. The photometer was a Hagner EC1 luxmeter (serial 8568),
held by the writer’s extended arm with the sensor facing up, its plane horizontal, about 1.2 m
above the pavement. Localised illuminance extrema (eg peaks from awning downlights and
shadows from trees and street furniture) were avoided when taking readings so that the results
would better represent the actual situation. The results have been plotted for every street
number. These values were found as the arithmetic mean of illuminances of odd and even
street number pairs after making linear interpolations at unit intervals along each side of the
street between observed illuminances. This tended to smooth the resulting illuminance
records but appears justified because the available crime data do not allow separation into
individual sides of the streets. In some cases, the even street numbers on one side of the street
were found to be displaced by up to ten metres or more from positions geometrically opposite
the preceding odd numbers but this appears to have little impact on the figures and the
conclusions drawn from them. No record of the arrest locations was present during the
measurements, nor had any attempt been made to memorise them.
78 On a casual basis, ie being in the city without any thought of observing drug dealing, the
writer and friends have observed presumed drug deals taking place by day and night in and
near both streets, sometimes within arm’s reach. The exchanges of parcels typically happen
so quickly as to suggest pre-arrangement.
79 See Part 1 for a description.
80 A good reason for limiting the time spent making observations was that the writer worked
alone and had to fend off occasional enquiries, politely, as to what was being done.
90