Outdoor Lighting and Crime - Amper

e at risk when community and environmental groups seek to quantify their complaints about
obtrusively relit commercial premises or sports grounds, or about larger-scale developments.
Regardless of the apparent dearth of useful numerical data on the growth in total light radiated
by outdoor lighting during the course of the twentieth century, there is no doubt that outdoor
lighting has grown from virtually nothing to the present unprecedentedly large values. As a
more or less constant minimum proportion of a city’s total outdoor light flux is scattered by
the atmosphere back towards any particular point on the ground (eg Fisher 1993),
measurements of this light (artificial skyglow) are a valuable independent source of
information about the rate of change in the total amount of light in the city.
The absolute quantity of light radiated upward at any time can also be derived from skyglow
measurements at that time or vice versa, albeit with a lot more effort (eg Garstang 2000a,
Falchi and Cinzano 2000). Periods in which observational data are of poor quality or nonexistent
can be dealt with satisfactorily by interpolation, assuming monotonic growth tied to
the known initial and observed recent values. This is especially useful for periods covering
the introduction of electric lighting as the natural skyglow value is reasonably well quantified
and the initial artificial skyglow value is effectively zero.
Incandescent lamps and their quartz-halogen derivatives are still in common use for outdoor
lighting although increasingly they are being supplanted by lamps using an electrical
discharge in low- or high-pressure gas. Relative to incandescent lamps, these newer types
tend to be between four to ten times better in turning electrical energy into light (eg IDA
IS115 1998). The successive introduction of improved lamps must have caused the total
amount of outdoor light flux to grow more quickly than the growth in electrical energy used
for making this light (eg Cinzano 2000d, Hänel 2000). The development of solid-state light
sources has now reached the stage where they also are increasing the range and affordability
of outdoor lighting, thereby further promoting the use of artificial light at night.
Historically, motivating factors that have led to more and brighter outdoor lighting include:
• facilitating pedestrian mobility and vehicular traffic at night by reducing the likelihood
of accidents and aiding wayfinding,
• allaying the fear of crime at night,
• attracting individuals to commercial venues such as bars, theatres and shops,
• the increasing popularity of outdoor sports at night for players, spectators and
television audiences,
• individual, corporate or national self-interest or self-aggrandisement, as with bright
lighting of power stations, illuminated advertising and architectural floodlighting,
• increasing luminous efficacy of lamps, giving more light for the amount and cost of
the power consumed,
• safety and productivity in outdoor industrial operations at night,
• promotional incentives by operators of thermal power stations to meet the base load
required at night for profitability, and
• as an intuitive countermeasure to actual crime.
General experience is that results seem to confirm expectations. In some cases, especially the
last two or three, however, most individuals have neither the analytical skills required nor
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