outdoor lighting and crime, part 1 - Astronomical Society of Victoria

7.2 LIGHTING FOR CCTV CAMERAS
Closed circuit television (CCTV) has been included in this document partly because it is
often in competition with street and other public lighting for government crime-prevention
funding. For 1996 through 1998, more than three quarters of spending by the UK Home
Office on crime prevention was for CCTV systems (Welsh and Farrington 2002, p 44 [116]).
Another reason is that it also has its own lighting requirements.
The last decade of the twentieth century saw a rapid rise in the deployment of video
surveillance, despite concerns about civil liberty and increasing imaging capability (Honess
and Charman 1992 [45]). Existing cameras need artificial light to operate properly at night.
Vermeulen (1992) [114] showed that a charge-coupled-device (ccd) video camera with a typical
good quality objective lens required a scene illuminance of 26 lux for excellent picture
quality. 23 The required values depend on the type of lamp in use.
Video cameras and high-pressure sodium lights were installed at metropolitan railway
stations in Melbourne about a decade ago (Carr and Spring 1993 [18]). The luminaires used
are fully shielded (ie, confining the directly emitted light to the horizontal direction and
below), but generally both the direct glare from the lights and the lit surfaces of the station
tend to be unpleasantly bright by comparison with illumination in most of the surrounding
area. Adjacent car parks for rail travellers are also overlit with semi cutoff high-pressure
sodium lamps, which are much worse as sources of glare.
A photometric survey 24 of two of the stations and one of the adjacent car parks indicated
that the horizontal illuminance in the carpark and bus shelter ranged from 25 lux to 71 lux.
On station ramps and platforms, the range was 88 lux to 452 lux, with a typical value of
about 300 lux, over ten times brighter than Vermeulen found to be sufficient for use with
CCTV, and also over ten times brighter than is required to reduce fear of crime to near
daylight values (Boyce et al. 2000 [14]).
The glare and steep illumination gradients cause visibility losses in the vicinity, particularly
for elderly persons and others with increased intraocular light scatter. It would appear
difficult to separate overbright lighting and presence of the cameras in any attempts to assess
effects on crime and fear of crime.
For video camera installations in general, attempts at cost cutting might increase the need
for bright lighting because brighter scenes allow the video camera lenses to be operated with
smaller aperture stops (numerically larger f-numbers). This allows the use of cheaper lenses
as prime cost items, but imposes greater prime costs for light fittings and greater operating
costs for electricity. The desire for sharp images over a greater range of distance could also
lead to demands for brighter lighting because smaller aperture stops give increased depth of
focus at the cost of dimmer images.
Note that for a given amount of illumination from a high-pressure sodium (HPS) lamp,
about 25 % more light is required from a low-pressure sodium (LPS) lamp for the same
picture quality (Vermeulen 1992 [114]). HPS is more effective because it is richer in red and
near-infrared radiation for which the ccd image sensors are relatively much more sensitive
than the eye is.
23Note that vertical plane illuminances of over 1000 lux are used for live colour TV broadcasting of sporting
events.
24The survey was conducted by members of the Outdoor Lighting Improvement Section of the Astronomical
Society of Victoria.
47