The
range that your camera will see in the dark will depend on the
sensitivity and spectral response of the camera and lens combination.
Some cameras have a better IR performance than others. For maximum
performance choose IR sensitive cameras.
The human eye cannot see infra-red light, however most mono
CCTV cameras can. As such the invisible light can be used to illuminate
a scene, this allows night time surveillance without the need for
additional artificial lighting. Infra-red also provides many other
benefits above conventional lighting. The infra-red beam shape can be
designed to optimise CCTV camera performance, as such it is important
to remember to design illumination for the CCTV camera and scheme.
Infra-red lamps cannot work with colour cameras. Normal
artificial light e.g. sodium light, causes problems to the quality of
the picture, not producing accurate colour quality. There are two
options: It is possible to use a mirrored shift filter lamp that
produces good colour rendition with a good quality low-light colour
camera or to use a dual technology camera (colour by day, monochrome at
night) together with IR lamps.
Bulb life is dependent on filament ruggedness, design and
power management and control. Standard IR lamps claim average life
between 2,000 to 5,000 hours. Choose lamps with long average bulb life
to reduce maintenance costs. For short-range, low power applications
consider LED products with a greater than 5-year life.
Infra-red lamps come in varying wavelengths from approx. 730nm
to 950nm. 730nm filters are overt and give a red glow - like a traffic
light. 830nm filters are semi-discreet and produce a dull red glow.
950nm filters are effectively totally covert - giving off no visible
illumination. Viewing distances are reduced with 830nm and 950nm lamps.
A 950nm will require a highly sensitive night time camera.
|
