Come on….admit it…the dark is scary. It’s filled with weird sounds and unknown shadows, and unless you are looking for a good Halloween scare, we just as soon try to avoid the whole eerie experience. It can be the same story when designing a perimeter surveillance system. It’s easy to get caught up in the perimeter layout, taking time to evaluate camera locations, lenses and image resolution only to forget that all that changes when the sun goes down and that scary darkness sets in. In most cases, the limiting factor in all surveillance coverage occurs at night. It may be a scary proposition, but you need to insure you are considering the darkness and asking the right questions: How do you intend to cover the scene in darkness? Will you use some type of illuminant, such as infrared or a visible light source, or perhaps the choice is a thermal sensor.
As an example, a camera that can cover a 500m fence line during the day may be reduced to 200m at night due to the type of illumination being considered. This not only impacts the layout, but obviously has consequences on the final budget. The dark also causes you to consider trade-offs: The use of an infrared illuminated camera will provide you some facial details and can allow viewing of license plates, but this adds a piece of equipment (mounting, power and maintenance) and is susceptible to weather conditions like rain, snow and fog. In contrast, a thermal camera will cost you a more and won’t be able to provide you facial or license plate details, but it copes better with weather conditions.
If you choose to use illumination, such as infrared or even white light, another important night time consideration is understanding that both the camera and the illuminator have an effective field of view (FOV) and they most likely are not the same. If you have ever viewed a camera at night with little or no illumination then you understand why this is important, you basically get a black video feed. If you want your night time FOV to correspond with your daylight FOV, then you need to insure that you illuminator beam matches your camera FOV in both distance and width.
Some illuminators have adjustments where you can make the beam narrow and long, or wide and short. Others have a fixed light pattern. In almost all cases, the resulting FOV which matches the illuminator’s capability will be a substantially shorter distance than what can be achieved with the camera alone in full daylight conditions. Not taking the FOV of your illuminant into consideration can be a costly mistake in terms of coverage. Considering the FOV of your illuminant should certainly take place during the planning phases, but also plan on staying up late and braving the darkness to insure the coverages match in the final installation.
Finally, walking around a facility at night may not be your idea of a good time, but when planning a perimeter surveillance installation, job site walks are an extremely valuable part of the security design process. That includes making the walk in the dark. If you are an integrator, consultant or involved in a facility’s security you or your company may have participated in many of these walks, but I’d be curious how many have been through a night time site walk? Most times these are thought as unnecessary, as a security design will typically include some type of consideration for low light viewing: infrared illuminators, thermal cameras, etc. However, there are many sources of existing light that need to be considered when setting a field of view: existing facility lights, periodic headlights, lights from adjacent facilities, sunrise/sunset, reflective light (water / windows), etc. Light sources can play havoc on cameras in a variety of ways, so it’s important to know where they are and to plan your FOV around them if possible. Unfortunately, if you don’t plan on staying up for the night shift, you won’t have the opportunity to explore where these lighting issues might be lurking.
The dark may be scary, but it’s a very important aspect when considering the design or enhancement of a perimeter surveillance system. So toughen up, grab your Toy Story flashlight and make sure your perimeter surveillance isn’t scared of the dark.