Outdoor Lighting and Crime - Amper

convert 1 watt of electrical energy into 683 lumens of green light (555 nm), or a lesser
number of lumens of white light, the amount depending on the spectral energy distribution.
Actual lamps tend to be much less efficaceous than this in producing their visible light output.
The actual electrical energy inputs required to produce the observed upward light losses are
expected to be between about five and ten times greater than the energy values given by Isobe
and Hamamura.
5.2.2 Upward light energy losses for various cities
The upwardly radiated light from a city, town or other populated area includes a substantial
component of unused waste light that is emitted above the horizontal directly from outdoor
light sources. These sources include advertising signs, road signs, traffic signal lights, and
vehicle lights. It is convenient to include here also the light radiated above the horizontal
from external windows of internally illuminated buildings, although part of it is used waste, ie
it has performed a useful function indoors. The balance consists of waste used light that has
been reflected above the horizontal from the terrain and built environment. As a first
approximation, the total light in space detected coming from a populated area is proportional
to the total amount of outdoor lighting within the area. Obviously, factors such as presence
and effectiveness of luminaire shielding, 57 extent of use and opacity of drapes and blinds at
windows, and the mix of light-coloured concrete and blacktop road and path surfaces will
affect the constant of proportionality. For the immediate purpose, accurate relative measures
of upward light energy loss between cities appear to be a sufficient guide to the relative
amounts of ambient artificial light available for human outdoor activities at night.
The Isobe and Hamamura data appear to have an acceptable degree of internal consistency,
although the authors warn of errors from sensor saturation by the bright centres of some cities.
A related point is that the nominal surface resolution of the satellite OLS system, 2.8 km, is
somewhat too large for accurate measures of the bright central lighting peaks of many cities
(eg NASA 2000).
These shortcomings in the data could result in local energy loss underestimation. Of the 153
cities listed, the ten cities with the largest amounts of upward light energy loss per square
kilometre are shown in Table 3, along with the ten having the smallest amounts. The
observed range in values is remarkable, even allowing for the effect of snow cover in inflating
some of the values (discussed below). Note that a high or low ranking for light loss per unit
area is not necessarily a good predictor of light loss per person.
57 Photometric measurements at and around observatories indicate that the proportion of fullcutoff
luminaires to other types is of much greater importance in limiting the lateral spread of
skyglow than is generally recognised by the lighting industry. This factor also affects the
ratio of ambient artificial light at the ground to the artificial light detected by satellites. The
convenience of temporarily ignoring this factor at this stage of the investigation is not in any
way intended to soften the case for the complete elimination of any source of outdoor light
with anything less than full-cutoff characteristics.
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