Most network cameras default to automatic gain control (AGC), and have circuitry that works to optimize the visual image. In very low light conditions, a camera’s ACG circuitry can boost the signal up to 100 times its original level. That would mean 100 times the level of noise in the image.
Even though the visual impact of the video noise is secondary and the main aspects of the target scene can still be seen by a human viewer, to the compression algorithm the noise constitutes tiny details in the image that are continuously changing — thus, compression techniques such as those used by H.264 video encoding are able to provide only slight compression.
A scene evenly-lit even by low levels of LED lighting can result in bandwidth reductions from 20 to 40 percent, according to field tests.
Optimizing LED for Surveillance
LED light from even small fixtures can be more intense than other types of lighting, especially when close to the lighting source — causing light-colored objects to wash out or creating flaring white spots in the video. This can occur with both with infrared and white LEDs. Close proximity to the source of light can result in washed-out facial images or vehicle license plates (which are highly reflective).
LED Lighting intended to support a specific camera should be adjusted by location, light focus, light width adjustment or a combination to match the camera’s field of view (FoV). The objective is to reduce lighting hot spots within the image. Field tests are appropriate — what has been found to work at initial LED test sites should be documented to provide design guidelines for the remaining sites selected for lighting improvement.
Before finalizing the exact position of lighting fixtures, such as at pedestrian or vehicle entryways, designers should perform field tests to determine: the maximum level of lighting that can be used without causing flare spots or wash-out; and the minimum level of lighting required to achieve an acceptable low-light video image with minimal noise.
Setting these levels as minimum and maximum standards of lighting for specific area types and activity levels can provide effective guidance for lighting device selection and placement.
A highly publicized case study is that of the Newport News Public Schools (NPSS), a school district in Newport News, Va., which in 2008 updated the campus lighting of its seven schools with LED lighting, achieving a 65-percent reduction in annual lighting energy costs.
Here are a few of the calculated savings from the seven-school project, which replaced 189 parking lot high-pressure sodium fixtures and 150 exterior building illumination incandescent fixtures with white LED lighting:
- Annual energy savings: 139,000 kWh
- Annual energy cost savings: $10,463
- Annual energy costs reduction: 65 percent
- Payback time: Three years
It becomes plain that the benefits of deploying LED lighting goes beyond simply improving the quality of video surveillance images. While the benefits of security video improvement may not be enough to make the business case, the other benefits — especially the cost-savings — can tip the scales in favor of project approval. And as LED lighting technology continues to improve, and as the cost of energy increases, the ROI from LED lighting will become even higher.
Ray Bernard, PSP, CHS-III is the principal consultant for Ray Bernard Consulting Services (RBCS), a firm that provides security consulting services for public and private facilities. For more information about Ray Bernard and RBCS go to www.go-rbcs.com or call 949-831-6788.