The Lowdown on Low Light

Network video technology for dusk-to-dawn surveillance


An owl’s nocturnal vision is legendary. It can spot the slightest movement in the shadows of night and swoop down on unsuspecting prey.

Human visual perception in the hours from dusk to dawn falls far short of that mark. We might be able to sense movement, but discerning details like facial features, license plate numbers or the colors of objects and clothing diminishes in direct correlation to the waning light. It is precisely why the criminal element is so active at night.

Security cameras face similar limitations, because their design mimics the human eye. The sensor — just like the retina — needs a certain amount of light to project an image. The iris in both the eye and camera controls how much light is focused on the sensor/retina. The lower the available light, the worse the picture quality.

Over the past decade, however, manufacturers have made great strides in camera sensor, design and lens technologies to bring nighttime vision to new levels. True day/night cameras with mechanical IR-cut filters were the first on the scene, followed by day/night cameras equipped with infrared illuminators. Next to reach the professional surveillance market were thermal imaging cameras designed to detect heat and “see” in complete darkness. But neither IR-assisted surveillance nor thermal imagery produce detail or color at night — both critical factors for identification.

The newest generation of IP cameras adds another dimension to nighttime surveillance. “Lightfinder” technology combines acute light sensitivity with enhanced image processing, allowing the camera to see a wealth of visual detail — in color — even in poorly lit environments as low as 0.05 lux (think dead of night with minimal street lamps illuminating the area).

While each of these low-light technologies feature specific strengths to improve surveillance at night, it is knowing how to deploy the different cameras in strategic harmony to create a surveillance system that surpasses even an owl’s night sight.

 

Under the Setting Sun: True Day/Night Cameras & IR Illuminators

Day/night cameras use infrared (IR) cut filters to stream the light in the visual spectrum. During the daytime, the filters “cut out” infrared light, which would distort image color when it hits the sensor. At nighttime, the filters automatically retract to allow the infrared light to reach the sensor and increase the camera’s light sensitivity. At the same time, the camera converts to black-and-white mode, since color distortion would occur without the filter in place. In black-and-white, a true day/night camera can see images down to 0.008 lux.

IR illuminators — covert and non-covert — provide additional luminosity when ambient light is insufficient. Covert IR illuminators enhance a day/night camera’s ability to capture images in the invisible spectrum. Non-covert illuminators help the camera sensors to detect objects in the near-visible infrared spectrum.

Where they work well: Day/night cameras with IR illuminators are good in pitch-black environments such as warehouse entrances with no ambient light or darkened office building interiors with few windows. Covert illuminators are impossible to detect with the naked eye.

Where they fall short: Non-covert illuminators generate a red aura that intruders can spot with infrared detection devices. Illuminators also add cost to the surveillance installation, both in capital investment and labor, as well as power consumption. Furthermore, in smoke or haze, their perception is as foggy as the human eye. The cameras’ images are also produced in black and white, which can hinder identification.

 

Thermal Imaging Cameras

While day/night cameras focus on recognizing images in the visible light spectrum, thermal imaging cameras detect wavelengths far into the infrared spectrum. Since all people and objects emit some level of infrared radiation — commonly known as a heat signature — thermal imaging cameras can spot people and objects under any lighting condition, in smoky and hazy environments, as well as in direct sunlight that would typically blind conventional cameras. A thermal camera can transmit the image of a human silhouette even if the person is dressed all in white in a snow-covered field.

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