Outdoor Lighting and Crime - Amper

Isobe 2003) with the same observational date, but for the Turkish cities only, the total energy
losses are about 14 % larger and the losses per unit area are up to 43 % larger. Data attributed
to Isobe and Hamamura are given by RASC (1999) for three additional cities in western North
America, but data for other cities in the region are as much as 25% less or nearly double the
values given for the same date in Isobe and Hamamura (1998) and Isobe (2000). The
additional cities are not included in the following analysis.
The electrical industry units used for light energy by Isobe and Hamamura are customary
rather than fully SI metric. They are reproduced here unchanged in two forms: one is
electrical energy radiated above the horizontal at night per year in gigawatt–hours (the total
light energy loss) for the whole city, and the other is this value divided by the city area in
square kilometres. A third form, derived in this paper, is the total light energy loss divided by
the city population to give per capita values. If these quantities did truly represent energies of
visible light for given operating durations, the first and third would be proportional to
luminous intensity and the second, with a different factor of proportionality, to mean
luminance. 56 The quantities involved are treated here as though they are photometric
quantities, although the approximation is crude.
The approximation is even poorer than is apparent because the photopic (cone vision) spectral
response implied is rather inappropriate. Given the generally low light levels involved, visual
quantities might more usefully be described in scotopic (rod vision) terms, or at least in
mesopic terms, a transitional mix of photopic and scotopic characteristics. By comparison
with the photopic spectral response, the scotopic response is displaced towards the violet end
of the spectrum. In this dim-light adaptive state, not only does the eye remain insensitive to
near infrared but it is also insensitive to red light. One consequence of this is that cities that
radiate relatively more incandescent lamp light and less gas-discharge lamp light than cities
with a typical mix would be visually fainter than would be indicated by the satellite measures.
Different kinds of lamps are in common use for outdoor purposes and their distinctive spectra
have been observed, separately and mixed, in airborne calibration of DMSP OLS nighttime
data (Elvidge and Jansen 1999). The present analysis does not take between-city differences
of lamp-type mixes into account as the information does not appear to be readily available, if
at all.
For brevity, the measures derived from satellite-based optical radiation are called light energy
losses in this paper. Given its exploratory nature, the analysis presented is considered
sufficiently robust for its purpose. In due course, upwardly radiated light losses will be
presumably become available as true photometric quantities. This could be expected to
reduce confounding contributions to the variance in correlations between light and crime
quantities.
The publication of satellite measures of upward light energy losses has stimulated debate on
energy conservation and greenhouse gas emissions relating to outdoor lighting.
Unfortunately, many of the arguments put to date have not taken account of inefficiencies in
the conversion of electrical energy into light energy. A perfectly efficient electric lamp would
56 It is not illuminance, as the mean reflectance value is involved. Nevertheless, illuminance
may be more useful in discussions, which implies the approximation that the cities concerned
have the same mean reflectance.
58