d e t e k t o r i n t e r n a t i o n a l · 7
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Lighting for network cameras
howtoobtainthebestnighttimeperformance
Detektor Security Academy is an educational concept in which
Detektor magazine, together with selected security technology leaders,
have cooperated to produce, distribute and promote essential information
about the opportunities that today's security technology can offer.
In this article, sponsored by Raytec and Axis, Detektor Security Acad-
emy will explain how security professionals can tackle some of the most
common practical issues when using lighting in conjunction with network
cameras to achieve high performance CCTV images at night. This is the
fifth article within Detektor Security Academy.
Sponsored by
SECURITY ACADEMY
LIGHTING FOR
NETWORK CAMERAS
detektor security academy
your CCTV image, using IR light-
ing with an IR band pass filter
lens on the camera will cut out
the glare from all other ambient
light apart from IR, for a crisp and
clear, evenly illuminated black and
white image.
Excessive lux levels
Axis Lightfinder Technology. Image
captured in absolute darkness with
only 50 percent brightness.
White-light off (50 metres).
White-light on (50 metres).
High performance, low light
camera technology such as the
Axis Lightfinder, requires as little
as 1 or 2 lux of effectively directed,
colour corrected white-light
illumination. Many traditional
"visible" lighting solutions aim
for high lux levels on the scene
this is not always required and it
can often result in reduced image
quality, excessive light pollution
and excessive energy consumption.
NB: Typical lux levels for CCTV
are between 3 and 7 lux.
Megapixel cameras
There is one simple rule to re-
member, if all other variables stay
or white-light LED illumination.
Not only does LED lighting
have an inherently low power
consumption, but it also lasts a lot
longer -typically around 10 years
and requires zero maintenance -
compared to a halogen light which
can last as little as five months.
Over this ten year period, there
are significant savings to be made
on energy consumption, running
costs, and labour.
Additionally, white-light can
be targeted and directed exactly
where needed. It can also be ac-
tivated via an external trigger on
a timer, to provide lighting only
when needed for a predetermined
amount of time to further save on
energy usage and light pollution.
This is referred to as "Lighting on
Demand".
Street lights
Often, users of security systems
may consider street lighting to be
a good enough solution to fully
illuminate a scene for capturing
CCTV images at night. The user
may be cautious about adding
additional visible illumination on
scene because of light pollution
concerns. For this scenario, infra-
red illumination which is invisible
to the human eye can be a very
effective solution.
If there is too much ambient
light on scene, or flashing lights
nearby causing a disturbance to
maximum light, more closed dur-
ing the daylight.
Con:
Auto iris lenses can often be
slightly bigger, and more difficult
to set-up.
Pro:
Fixed lenses are often used
for internal applications where
light levels may be constant, and
can be set to the specific scene
requirements. The smaller the
F-stop setting on the camera is
fixed at (1.4 is typical for night
time surveillance) - the wider the
iris, therefore more light is let into
the camera and it produces better
night-time images. The camera
will use an electronic iris during
the day (like a shutter) to avoid
too much light causing over expo-
sure (white out) on a scene.
Con:
Fixed lenses are not suitable
for day/night or changing light
scenarios. The iris opening cannot
be adjusted. To compensate for
changes in light, some cameras
will adjust exposure time or gain,
which can lead to motion blur or
noisy images.
Lighting cost
Consider the running and mainte-
nance costs of your system. Many
installations utilize multiple 300W
or 500W illuminations. These can
be replaced with as little as 40W
of long life, cool running infrared
and even illumination, and no
dark spots.
Infrared and focus shift
Focus shift is a potential is-
sue encountered when setting
up camera systems for 24-hour
performance using infrared. The
different wavelengths of visible
light (400-700nm) and infrared
(700-1,000nm) create different
focus points through the lens onto
the camera chip. This can lead
to a loss of image focus at night,
particularly if the camera is set up
during daytime operation. The
degree of focus shift depends on a
variety of factors.
Focusing the camera correctly
for low light performance means
the camera will be focused for
IR with the aperture fully open.
During daytime operation the
increased depth of field created
by a closing aperture will counter
the effects of focus shift. The best
solution is to focus the camera
using only infrared. This can be
achieved by setting up the camera
at night using infrared lighting
and using an IR pass filter over the
camera lens.
Lenses
The choice of lens impacts the
quality of image. Here are some
pros and cons regarding lenses.
Pro:
A camera with an auto iris
lens (like many of the Axis cam-
eras) is the common choice for
achieving high quality images for
24 hour surveillance in external
scenarios. The auto iris opens and
closes to allow the right amount
of light fall onto the camera chip
dependent on whether it is day
or night. Open at night to collect
Street lighting.
Infrared on.