Security Lighting Do’s and Don’ts
Article from http://vintechnology.com/2011/12/22/security-lighting-dos-and-donts/
Correct lighting is Major key in a Home or Business security system, and when used properly in conjunction with your security cameras, you will be sure to capture all the important footage with maxium clarity.
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Consider 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.
Consider lighting position carefully. 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.
Reduce and prevent glare. Glare will obstruct the camera’s view, and actually encourage criminals to strike. Studies have shown that criminals are aware of CCTV cameras that have too much glare, and actively exploit it. Multiple lamps of moderate power instead of a few powerful lamps will reduce glare, provide more even illumination with reduced pools of shadow, and provide some redundancy if one lamp’s bulb blows out or develops a bad ballast.
Prevent malicious tampering or interference. This means that besides the lamp itself, the entire circuit from the source (electronic or generator), through the wires, to the lamp and back should be protected.
Lighting should be accessible enough to maintain but not be tampered with.Make sure the lighting is positioned easily enough to replace blown bulbs as quickly as possible and clean them periodically. However, they should be protected or somehow made inaccessible to tampering.
Consider infrared lighting. Infrared (IR) or near infrared has a spectrum of lighting 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.
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Avoid making lighting TOO bright. Shielded or full cut-off (FCO) lamp housing conceal the bulb, and should direct light onto the ground or target away from observers. These lights should send no light above 80 degrees from the nadir, or the direction pointing directly below a particular location.
Lighting should be bright enough, and not as bright as possible. In many cases, a good rule of thumb is 0.5 watts per square metre (0.05 watts per square foot), or a minimum illumination level of 1.5 foot-candles, 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. This may be increased in very congested environments, but conversely can be reduced in very open environments.
Don’t leave the electrical meter box open.
Ensure the electric meter box is locked or inaccessible, or else power the lights from a different line.
Ideally, multiple circuits should be used to prevent an accidental or malicious short or cut causing all illumination to fail.
Don’t forget the “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.
Don’t under or overestimate the 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.
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