UFC 4-021-02NF
27 September 2006
change 1, 23 October 2006
4-9.2.2 The second technique is the use of cameras with automatic gain control, a
feature that amplifies existing video to help camera create an enhanced video signal at
low light levels.
4-9.2.3 Both of these techniques enable cameras to function more effectively in
interior low-light conditions, and are also useful for outdoor cameras as well. In some
cases, the integration of CCTV cameras with night-lights and intrusion sensors can be
very effective. The sequence of events might be as follows: an intruder activates an
interior presence sensor, which in turn activates instant-on lighting or a night-light, and
the CCTV camera is triggered and video images are recorded.
4-9.3
Light-to-Dark Ratio. One design parameter of CCTV systems is specification
of a proper light-to-dark ratio in the space viewed. "Light-to-dark" ratio refers to the light
intensity (as measured in foot-candles or LUX) of the lightest (most reflective surface) to
the darkest (least reflective surface). A proper light-to-dark ratio for good CCTV picture
clarity is 4:1. The maximum ratio is 8:1. When the ratio is too high, the shadows appear
black and the viewer can not distinguish any shapes in the shadows. While not always
achievable, the designer should strive for a light-to-dark ratio of 4:1, as shown in Table
4-3. For guidance on light sources and lighting levels, refer to UFC 3-530-01.
Table 4-3. Light-to-Dark Ratios
Light-to-Dark
Quality of Image
Ratio
4:1
Great
6:1
Good
8:1
Marginally acceptable
4-9.3.1 The CCTV system designer can influence the light-to-dark ratio by
coordinating with the project's lighting engineer, landscape engineer and interior
designer. Actions the designer can take to achieve a proper light-to-dark ratio include:
4-9.3.1.1 Positioning of lighting.
4-9.3.1.2 Positioning of cameras.
4-9.3.2 When cameras and lights are mounted in close proximity, take care that the
light does not interfere with the field-of-view of the camera, such that glare or
backlighting issues do not occur.
4-9.3.3
Adjusting the field-of-view.
4-9.3.4
Selecting building surface interiors to minimize contrasts
4-9.3.5 Engagement of lighting engineers for new construction projects allows
modeling of light-to-dark ratios for different material selection; such as concrete versus
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