Lurking in the Shadows

The benefits of using day/night cameras, IR illuminators and thermal cameras

• By Fredrik Nilsson
• Aug 01, 2010

Mal-intended people operate under the cover of night, knowing that darkness makes it hard for them to be detected and identified.

While it is difficult for humans to see in darkness, our eyes compensate by opening the iris. But a wide-open iris is easily blinded by sudden, direct illumination.

Video cameras work in a similar way. Like human eyes, cameras also have irises that expand and contract to adjust for ambient light. In some cameras, built-in auto-iris control software automatically adjusts the iris opening. While this feature somewhat improves a camera’s light sensitivity under certain conditions, the camera still would not be able to detect everything in a dark scene. Furthermore, the lens can still be easily blinded by sudden, direct light.

Beyond poor lighting, haze and smoke present even greater challenges to visibility. Under these conditions, the human eye is generally incapable of discerning much detail. But advances in video surveillance technology are enabling today’s cameras to see beyond the limits of the human eye. True day/night cameras, day/night cameras equipped with IR illuminators and thermal imaging cameras enhance visibility under trying conditions that would defeat the abilities of standard imaging cameras.

Boosting Visibility After Sundown
Light comes in different wavelengths. Humans are able to see wavelengths between 400 and 750 nanometers. While higher wavelengths are not visible to the naked eye, most camera sensors can see up to 1,000 nanometers, which is well into the infrared spectrum.

But, to make those images detectable within our visible spectrum, manufacturers of day/night cameras employ an IR-cut filter, which filters out infrared light so it does not distort the color of images. In low light, the camera automatically retracts the IR-cut filter, allowing the infrared light to reach the sensor and enabling the camera’s light sensitivity to reach 0.001 lux.

At the same time, the camera automatically converts to black-and-white mode since colors would appear distorted without the IR-cut filter in place.

Day/night camera technology is widely available in today’s surveillance cameras, which can be mounted in regular enclosures. While they cost more than cameras without day/night technology, they are still the lowest-cost technology for night vision.

Day/night cameras are especially useful in environments that restrict the use of artificial light, such as residential areas, or in nighttime traffic surveillance.

Day/night cameras also are optimal for low-light video surveillance, such as in a retail store where lights are dimmed at night, or for city surveillance where widely spaced street lighting is available.

Seeing in Pitch Black
IR illuminators are designed to enhance the nighttime performance of day/night cameras. As high-performance white and infrared LEDs, IR illuminators provide additional luminosity in the 800 to 1,000 nanometer range. They give users the unique flexibility to alter the angle of on-site illumination to suit various security needs and match a day/night camera’s field of view. Covert illuminators enhance the camera’s ability to capture images in the invisible spectrum. Noncovert illuminators enhance the camera’s sensors to detect objects in the near-visible infrared spectrum.

Compared to traditional light bulbs, illuminators are highly energy efficient. With a typical lifecycle of up to 10 years, illuminators provide huge savings in long-term operational and maintenance costs.

Day/night cameras enhanced with IR illuminators also are especially useful in pitch black environments. More importantly, covert illuminators are impossible to detect with the naked eye.

But with any surveillance technology, users need to be aware of their limitations. Non-covert illuminators generate a red aura that intruders can discern with infrared detection devices. Plus, illuminators add to the cost of the surveillance installation and maintenance, not only in capital investment and labor but also in power consumption. Another drawback with day/ night cameras with or without IR illuminators is that they cannot see through smoke or haze.

Detecting Heat Signatures
In contrast to day/night cameras that recognize visible light up to 750 nanometers, thermal imaging cameras recognize wavelengths of up to 14,000 nanometers— well into the far end of the infrared spectrum. Since all people and objects emit some level of infrared radiation, thermal cameras can be used to detect objects and people, not only irrespective of the lighting condition, but also of smoke, haze and other challenging weather conditions.

For instance, even if a person is dressed head-totoe in white clothing in a snowy backdrop or garbed in black while lurking in a shadowy forest, the camera can see the heat signature radiating from the human silhouette. This detection ability also holds true in difficult weather conditions, which would blind conventional cameras.

Additionally, for installations where there are privacy concerns, thermal cameras allow for anonymous surveillance since the technology does not depict facial features. It does, however, provide sufficient information about the scene and helps eliminate false alarms.

Because thermal cameras can “see” into shadows, where intruders might hide, the application potential for this technology is enormous. Thermal cameras can be deployed in residential neighborhoods without concern for light pollution. They can protect lengthy perimeters that lie in complete darkness, such as waterfronts and prison yards. Their placement in dangerous areas, such as busy roadways and railway tracks, can help security staff quickly spot people in danger, reducing the risk of accidents and death.

Until now, thermal cameras were too costly for average users. But with the introduction of new sensors and materials, coupled with economies of scale and the ease of installation and integration of IP-based technology, there are more attractive price levels for a wider deployment of thermal cameras. In addition to affordability, network thermal cameras can easily be integrated into existing IP infrastructure to complement a variety of video surveillance systems.