Formats/Resolution
Focal Length/Field Of View
Tips/Guides
Need more
information on
video
surveillance?
Can't decide
what camera will
best fit your
application?
Among other
information,
this section
contains
excerpts from a
research report
from the
National
Criminal Justice
Reference
Service that
may assist you
in your
decisions.
Lighting
requirements and
nighttime
applications
For exterior
nighttime CCTV
applications,
proper lighting
is very
important. A
number of
lighting types
are available.
These types
include
incandescent,
fluorescent, and
high-intensity
discharge.
Incandescent
lighting is the
most expensive
to operate and
includes the
flood or quartz
lights that are
commonly used
for exterior
home security
applications.
Most fluorescent
lighting is used
indoors for
office and work
area lighting.
High-intensity
discharge
lighting is the
least expensive
to operate (more
light is
produced with
less power
consumption) and
is the most
common for
commercial
exterior
lighting
applications. It
includes
high-pressure
sodium and
low-pressure
sodium lighting.
A disadvantage
of
high-intensity
discharge
lighting is the
restrike time.
If a momentary
power outage
occurs, these
lights will go
out and can take
up to several
minutes to
return to full
brightness. The
advantages of
high- and
low-pressure
sodium lighting,
however,
outweigh this
disadvantage for
CCTV
applications.
Low-pressure
sodium lighting
is the most
desirable choice
for exterior
CCTV
applications
because it is
somewhat more
efficient to
operate than
high-pressure
sodium, and the
types of light
fixtures
available
provide a fairly
uniform light
pattern. A
disadvantage to
low-pressure
sodium is the
monochromatic
yellow light it
produces, which
some people find
objectionable.
Important
items to
consider for
nighttime camera
lighting are
illumination
level, camera
sensitivity,
lens type,
light-to-dark
ratio, area of
illumination in
the camera field
of view, and
lighting
position. Note:
These are not
simple issues to
be addressed by
a neophyte. Be
certain that you
discuss lighting
issues with your
local power
company or
lighting expert.
Illumination
level, camera
sensitivity, and
lens type .
Lighting levels
must be high
enough for the
camera to
produce a
useable image.
The light level
required will
depend on camera
sensitivity and
lens type and
quality.
Black-and-white
cameras
generally have
more light
sensitivity than
color cameras
and are
recommended for
most nighttime
applications. A
minimum
illumination
level of 1.5
foot-candles
(approx. 16 lux),
as measured on a
horizontal plane
1 foot off the
ground, is
recommended for
a
black-and-white
camera with a
sensitivity
specification of
0.007 foot-
candles
faceplate
illumination.
This assumes the
camera has a
good-quality,
F/1.4 fixed
focal lens. A
color camera or
a camera with a
zoom lens will
require a higher
light level in
order to get
equivalent
brightness and
contrast.
Light-to-dark
ratio . A
recommended
maximum
light-to-dark
lighting ratio
is 6 to 1 (as
measured on a
horizontal plane
1 foot off the
ground). This
maximum applies
to the entire
area of interest
that the camera
is viewing. It
is also
recommended to
design the
lighting for a
4-to-1 ratio to
allow for some
degradation over
time. A 6-to-1
light-to-dark
ratio will
prevent areas
that are so dark
or so bright
that a person or
object would be
obscured.
Area of
illumination in
the camera field
of view
. A
minimum
illumination of
70 percent of
the camera field
of view is
recommended. A
camera is an
averaging
device. If too
little of the
field of view is
illuminated, the
camera will
average between
the illuminated
areas and the
nonilluminated
areas, resulting
in blooming and
loss of picture
detail in the
illuminated
area.
Lighting
position .
The position of
lighting in
relation to the
camera field of
view is also
important. As
much as
possible, light
sources must be
kept out of the
camera's field
of view. Lights
that are
illuminating a
camera scene
should be
mounted higher
than the
cameras. When
determining a
location and
field of view
for a camera,
extraneous light
sources, such as
building-mounted
lighting for
pedestrians that
will be in the
camera view,
must be
considered.
Extraneous light
sources can
cause blooming
and streaking in
a camera,
rendering
portions of the
field of view
unusable.
Distant light
sources that are
relatively dim
are usually not
a problem.
Other
lighting .
Another type of
lighting is
known as
infrared (IR) or
near infrared.
The spectrum for
this lighting is
just below red
and is not
visible to the
human eye. Most
black-and-white
cameras have
sensitivity into
the infrared. A
black-and-white
camera can be
used with this
type of lighting
to observe areas
at night without
having lighting
that is visible
to humans. To
make use of IR
lighting, the
camera must not
have an IR cut
filter. Cameras
can be ordered
without IR cut
filters; be sure
to specify no IR
cut filter when
ordering.
Commercial IR
light sources
include
incandescent and
the light
emitting diode
(LED). The
incandescent
type typically
use a 300- to
500-watt lamp
and a visible
light cut
filter. 2,000
hours is a
nominal life
expectancy of
the incandescent
lamp. The LED
type emits light
in the IR, but
uses less power
and has a much
longer life
expectancy. The
incandescent
type will
provide more
illumination
than the LED
type. With
either type of
IR light, more
light fixtures
will be required
to illuminate an
area than with
visible
lighting. While
IR lighting has
the advantage of
not being
visible to
humans, it is
fairly
expensive.
