What is Night Vision mode?

Most thermal-imaging devices scan at a rate of 30 times per second. They can sense temperatures ranging from -4 degrees Fahrenheit (-20 degrees Celsius) to 3,600 F (2,000 C), and can normally detect changes in temperature of about 0.4 F (0.2 C).

There are two common types of thermal-imaging devices:

• Un-cooled — This is the most common type of thermal-imaging device. The infrared-detector elements are contained in a unit that operates at room temperature. This type of system is completely quiet, activates immediately and has the battery built right in.
• Cryogenically cooled — More expensive and more susceptible to damage from rugged use, these systems have the elements sealed inside a container that cools them to below 32 F (zero C). The advantage of such a system is the incredible resolution and sensitivity that result from cooling the elements. Cryogenically-cooled systems can «see» a difference as small as 0.2 F (0.1 C) from more than 1,000 ft (300 m) away, which is enough to tell if a person is holding a gun at that distance!

While thermal imaging is great for detecting people or working in near-absolute darkness, most night-vision equipment uses image-enhancement technology.

The image-intensifier tube changes photons to electrons and back again.

Image-enhancement technology is what most people think of when you talk about night vision. In fact, image-enhancement systems are normally called přístroje pro noční vidění (NVDs). NVDs rely on a special tube, called an trubice zesilovače obrazu, to collect and amplify infrared and visible light.

Here’s how image enhancement works:

1. A conventional lens, called the objektiv, captures ambient light and some near-infrared light.
2. The gathered light is sent to the image-intensifier tube. In most NVDs, the power supply for the image-intensifier tube receives power from two N-Cell or two «AA» batteries. The tube outputs a high voltage, about 5,000 volts, to the image-tube components.
3. The image-intensifier tube has a fotokatoda, which is used to convert the photons of light energy into electrons.
4. As the electrons pass through the tube, similar electrons are released from atoms in the tube, multiplying the original number of electrons by a factor of thousands through the use of a mikrokanálová deska (MCP) in the tube. An MCP is a tiny glass disc that has millions of microscopic holes (microchannels) in it, made using fiber-optic technology. The MCP is contained in a vacuum and has metal electrodes on either side of the disc. Each channel is about 45 times longer than it is wide, and it works as an electron multiplier. When the electrons from the photo cathode hit the first electrode of the MCP, they are accelerated into the glass microchannels by the 5,000-V bursts being sent between the electrode pair. As electrons pass through the microchannels, they cause thousands of other electrons to be released in each channel using a process called cascaded secondary emission. Basically, the original electrons collide with the side of the channel, exciting atoms and causing other electrons to be released. These new electrons also collide with other atoms, creating a chain reaction that results in thousands of electrons leaving the channel where only a few entered. An interesting fact is that the microchannels in the MCP are created at a slight angle (about a 5-degree to 8-degree bias) to encourage electron collisions and reduce both ion and direct-light feedback from the phosphors on the output side.
5. At the end of the image-intensifier tube, the electrons hit a screen coated with phosphors. These electrons maintain their position in relation to the channel they passed through, which provides a perfect image since the electrons stay in the same alignment as the original photons. The energy of the electrons causes the phosphors to reach an excited state and release photons. These phosphors create the green image on the screen that has come to characterize night vision.
6. The green phosphor image is viewed through another lens, called the oční čočka, which allows you to magnify and focus the image. The NVD may be connected to an electronic display, such as a monitor, or the image may be viewed directly through the ocular lens.

NVDs come in a variety of styles, including ones that can be mounted to cameras.

Photo courtesy of B.E. Meyers Company

NVDs have been around for more than 40 years. They are categorized by generace. Each substantial change in NVD technology establishes a new generation.

• Generace 0 — The original night-vision system created by the United States Army and used in World War II and the Korean War, these NVDs use aktivní infračervené. This means that a projection unit, called an IR iluminátor, is attached to the NVD. The unit projects a beam of near-infrared light, similar to the beam of a normal flashlight. Invisible to the naked eye, this beam reflects off objects and bounces back to the lens of the NVD. These systems use an anode in conjunction with the cathode to accelerate the electrons. The problem with that approach is that the acceleration of the electrons distorts the image and greatly decreases the life of the tube. Another major problem with this technology in its original military use was that it was quickly duplicated by hostile nations, which allowed enemy soldiers to use their own NVDs to see the infrared beam projected by the device.
• Generace 1 — The next generation of NVDs moved away from active infrared, using pasivní infračervené instead. Once dubbed Světlo hvězd by the U.S. Army, these NVDs use ambient light provided by the moon and stars to augment the normal amounts of reflected infrared in the environment. This means that they did not require a source of projected infrared light. This also means that they do not work very well on cloudy or moonless nights. Generation-1 NVDs use the same image-intensifier tube technology as Generation 0, with both cathode and anode, so image distortion and short tube life are still a problem.
• Generace 2 — Major improvements in image-intensifier tubes resulted in Generation-2 NVDs. They offer improved resolution and performance over Generation-1 devices, and are considerably more reliable. The biggest gain in Generation 2 is the ability to see in extremely low light conditions, such as a moonless night. This increased sensitivity is due to the addition of the microchannel plate to the image-intensifier tube. Since the MCP actually increases the number of electrons instead of just accelerating the original ones, the images are significantly less distorted and brighter than earlier-generation NVDs.
• Generace 3 — Generation 3 is currently used by the U.S. military. While there are no substantial changes in the underlying technology from Generation 2, these NVDs have even better resolution and sensitivity. This is because the photo cathode is made using arsenid gallia, which is very efficient at converting photons to electrons. Additionally, the MCP is coated with an ion barrier, which dramatically increases the life of the tube.
• Generace 4 — What is generally known as Generation 4 or «filmless and gated» technology shows significant overall improvement in both low- and high-level light environments. The removal of the ion barrier from the MCP that was added in Generation 3 technology reduces the background noise and thereby enhances the signal to noise ratio. Removing the ion film actually allows more electrons to reach the amplification stage so that the images are significantly less distorted and brighter. The addition of an automatic gated power supply system allows the photocathode voltage to switch on and off rapidly, thereby enabling the NVD to respond to a fluctuation in lighting conditions in an instant. This capability is a critical advance in NVD systems, in that it allows the NVD user to quickly move from high-light to low-light (or from low-light to high-light) environments without any halting effects. For example, consider the ubiquitous movie scene where an agent using night vision goggles is “sightless” when someone turns on a light nearby. With the new, gated power feature, the change in lighting wouldn’t have the same impact; the improved NVD would respond immediately to the lighting change.

Many of the so-called «bargain» night-vision scopes use Generation-0 or Generation-1 technology, and may be disappointing if you expect the sensitivity of the devices used by professionals. Generation-2, Generation-3 and Generation 4 NVDs are typically expensive to purchase, but they will last if properly cared for. Also, any NVD can benefit from the use of an IR Illuminator in very dark areas where there is almost no ambient light to collect.

A cool thing to note is that every single image-intensifier tube is put through rigorous tests to see if it meets the requirements set forth by the military. Tubes that do are classified as MILSPEC. Tubes that fail to meet military requirements in even a single category are classified as COMSPEC.

Cameras with night vision are used to maximize a video surveillance system’s effectiveness in low light conditions. The fundamental feature that unites all such cameras is the presence of IR illumination, without which it is impossible even to imagine video surveillance at night. You need to know certain points not to be disappointed with the purchase when buying a camera with night vision , and we will now talk about them.

Features of night surveillance cameras

A good camera with night vision should have several relevant characteristics:

• Powerful IR illumination, preferably adaptive;
• Ability to switch from color mode to black and white;
• High light sensitivity of the sensor;
• ICR filter;
• Weatherproof housing.

Backlight. The first point is mandatory if you need quality night photography. You should pay attention to the backlight parameters declared by the manufacturer:

• Illumination angle;
• Range of action;
• Provedení.

The backlight angle should ideally coincide with the angle of view of the camera lens. Otherwise, the image can get a bright spot in the middle of the frame and dark areas at the edges.

Its power determines the range of the IR illumination, and the greater this parameter, the more power will be required to power it. For example, to provide a distance exceeding 10 meters, the backlight diodes must have a total power of 5-10 W, while the current consumption can increase to 1 ampere. Due to the increased energy consumption, the LEDs of IR illumination rather heat up during operation. Therefore, when located in the cameras with night vision bodies, cooling radiators will be required.

A reasonable way out of the above situations is the utilization of home security cameras with night vision , which have similar spotlights outside the hull.

Cameras with night vision: selection categories

1. Den noc: The ability to automatically switch from color to black-and-white and vice versa is also a must when choosing cameras with night vision because the camera is the best shooting in monochrome in the dark. Now, most IP view cameras are equipped with a day/night mode, but if this function is absent in the cameras with night vision , don’t rush to buy it at night in the color mode, the image quality will not be satisfactory.
2. Citlivost: Now let’s talk about the light sensitivity of the sensor. For video surveillance in the dark, the camera matrix’s sensitivity should be as high as possible. For example, to obtain a normal image on a moonless night with a clear starry sky, the camera must have a sensitivity of 0.001 lux. With this sensitivity, the home security cameras with night vision can produce a decent black and white image at night.
3. ICR filter: The ICR filter is a movable mechanical IR cut filter located in front of the cameras with a night vision sensor. T he human eye cannot notice the IR illumination light, but the camera sensor sees it perfectly. If the picture quality remains good enough at night in monochrome mode, then the IR radiation has a significant effect on the image in the daytime. Deterioration of quality manifests itself in color distortion, contrast, and image blur. Also, the home security cameras with night vision are equipped with an IR cut filter to protect against rays. During the day, the filter closes the matrix, and with the onset of darkness, it shifts to the side.
4. Bydlení: Suppose a video surveillance cameras with night vision is planned to be installed outside. In that case, it is worth purchasing devices with a special protective case that can withstand high and low temperatures and adverse environmental factors – dust and moisture. Usually, outdoor cameras with night vision are equipped with an anti-vandal hermetically sealed thermal casing capable of operating the device in the temperature range from -40 to 50 ° C, with a protection class IP66 – dust and moisture resistant. In some cases, the housing can be equipped with a heating system.

Three features of CCTV cameras for night vision

Сameras with night vision have their characteristics that are specific only for this type of device. These features can also be attributed to the disadvantages of night cameras:

1. High sensitivity to the presence of small particles in the air – dust, rain, snow;
2. Image ripple when working with unstable energy sources;
3. Limited resources of IR LEDs:

• Snow, raindrops, or dust, falling into the field of view of the camera lens at night, tend to reflect the light of the IR illumination from itself. At the same time, it becomes almost impossible to distinguish something on the monitor screen. This happens only in a heavy snowstorm or pouring rain, but, unfortunately, other options for night video surveillance cameras without IR illumination have a high cost.
• Image ripple can occur primarily due to the difference between the camera’s recording rate (fps) and the backlight ripple rate.
• The service life of IR LEDs in CCTV cameras is limited, ranging from 20,000 to 50,000 hours. Thus, with an average operating time of the backlight of 12 hours per day, the service life is limited from 5 to 10 years, after which the LEDs will need to be replaced, or alternative sources of illumination – IR illuminators – must be used. Otherwise, the camera will no longer be suitable for night shooting. A blizzard with rain is not so often, therefore, night video surveillance cameras with IR illumination are a very good solution.

Today, the vast majority of CCTV cameras are equipped with IR illumination. Cameras with powerful IR illuminators are now quite difficult to find – most of the models have been discontinued. These cameras have remote IR illumination on the sides of the case and have the characteristics of cameras with IR illumination with increased power. The illumination of such devices is based on the continuous wave, electro-optical illumination. Such cameras can recognize license plates and faces of people at a distance of up to 200-400 meters. Longer range is achieved through the 120x zoom capability.