Setting up
security systems in any environment that lacks adequate lighting is both challenging and demanding. Poor or non-existent lighting conditions require specific technology and installation techniques, as errors in the selection, installation, and application of cameras and their peripherals will affect performance quality. This article explores the selection and installation of infrared and
night-vision/low-lux cameras.
Understanding Low-Lux and Night-Vision Cameras
The first step in the selection process of low-lux or night-vision cameras is an understanding of the various applications that require low-light and night-vision features, in addition to the camera specifications. This ensures that the most appropriate cameras are selected for the environment of the project in question.
Low-lux surveillance generally refers to cameras that are able to capture images of viewable quality in low-light conditions without the need for auxiliary lights. Factors affecting performance include the combined effects of the sensors, the image processing unit, ISP/DSP, and the lens optics, all of which play a part in determining the actual performance of cameras under low-lux and night-vision conditions. The following are several ways to achieve the desired results.
Most Frequently Used: Low-Light Mode
Cameras featuring this low-light, high-sensing mode — also known as low-light, full-color mode - utilize Super HAD, Ex-view/EXTRA-View CCD, or back-illuminated CMOS sensors. These sensors perform well in low-light conditions with good visibility and near-IR reactions. Cameras using this technology tend to perform well under various weather conditions and function as
day/night cameras, as they are able to capture color images in both daytime and low-lux conditions. Generally speaking, low lux can reach 0.1 lux in color mode and 0.01 lux in black/white mode. IR illuminators providing near-IR light can be used in conjunction in 0 lux conditions, but these are generally not listed as part of the low-light, color-mode specifications. Most of these type of cameras utilize Ex-view-HAD technology, which are capable of performing in conditions of up to 0.01to 0.001 lux. Such cameras are not only able to capture clear images, but are also able to limit noise levels in color images taken under low-lux conditions, without the need to reduce shutter speed or increase iris diameter. Hence, they are considered to be capable of achieving low-lux surveillance.
Most Convenient: Day/Night Mode
Cameras featuring day/night modes use mechanical principals and are gradually becoming more common on the market. Most day/night cameras are labeled as colored 0.1 lux and IRC on black/white 0.01 to 0.001lux. It should be noted that since 0 lux does not really mean anything in this context, therefore, no special explanation of it is needed for low-light nighttime application. These cameras make use of near-IR light to deliver black and white images when light is reduced to a certain level - the camera switches to IR cut or to black/white mode after sensing the lower IR levels through the IR filter, and the images are converted from color to black and white.
When the IR-cut filter is removed during the conversion, however, the focus of the image is shifted. Hence, IR lenses are generally used to prevent a shifting of focus or inaccurate color displays, and to maintain consistency between the images taken during the day and at night.
Although uptake of such cameras is increasing, IR lenses are higher in cost and inevitably increase investment costs for the end user. In other words, they may not be the most ideal choice for low-lux applications.
Last Resort: IR Illumination Mode
This method involves the use of an IR illuminator to light up the areas of surveillance. Apart from day/night cameras,
IR cameras, as they are called, are one of the best applications for low-lux settings. The IR illuminator can either be an add-on module to the camera or be integrated in the camera housing. Since CCD and CMOS sensors already boast incredible light-sensitivity and are able to capture the majority of visible light and IR spectrum, IR illuminators enhance images in nighttime environments by allowing the image sensors to capture sharper images. Clearer images are also captured in dark conditions because light sensitivity under black/white mode is already higher than under color mode.
IR illumination makes it possible to set up
surveillance systems under 0 lux conditions. Its automatic light detection feature also allows this application to be used with either
black/white or day/night cameras to enhance low-lux and night-vision surveillance capabilities.
Most Risky: Digital Slow Shutter
The last camera application is achieved through slowing down the camera's electronic shutter speed, thereby prolonging the sensor's exposure to light to capture brighter pictures. Sometimes known as frame-accumulation mode, it utilizes digital slow shutter technology to electronically "accumulate" frames captured in inadequate lighting to build a clearer image. For example, an aperture setting of f1.2 to 1.4 captures enough frames in low-light conditions to reach 0.001lux. For some, this is a simple yet reliable way of achieving results in low-light conditions. However, DSS technology is best used in low-light conditions with
fixed cameras and in environments with minimal light changes; under other conditions blurred or lagged images are more likely to occur. Consequently, it is most suitable for sites where there is minimal movement and the use of IR or auxiliary lights are prohibited.
The four aforementioned products can serve as a basis when considering and selecting products for low-light and night-vision applications. The next step is to discuss the installation so that the best results are achieved.
Rules For Selecting IR and Low-Lux Products
The comprehensiveness of a complete, well-designed system depends on the appropriate selection of
IR and night-vision surveillance products. Thorough consideration of the camera and its peripheral products — such as IR lights, lenses, protective cover, and power supply — is required prior to determining whether or not IR illuminators would be compatible with the products and/or affect the quality of the images.
The following section provides some guidelines to ensure product compatibility, as well as ensure the safety of those installing the products.
Paying Attention to the Camera's Aperture
Aperture size is decreasing and the market currently provides a range of 1/1.8" to 1/4". The aperture size determines the amount of light that can pass through the lens and reach the image sensor — a larger aperture allows for more exposure, while a smaller one allows for less. Another thing worth paying attention to is the lens, as the focal length and aperture size are inversely proportional. For example, lenses of 4mm can achieve an aperture of f1.2 to1.4, but lenses of 50mm to 200mm can only achieve a maximum aperture of f1.8 to 2.2. Consequently, this affects light exposure, and when used with an IR filter, can also affect color accuracy.
Identifying Cameras that Require Low-Light Features
A camera's minimum illumination rating specifies the lowest threshold of lighting conditions for it to record video/images of viewable quality. Camera manufacturers will specify the lowest f-stop for different apertures, which is also the camera's minimum illumination or sensitivity rate. If the camera's minimum illumination rate is higher than the IR illuminator's spectrum, the effective distance will be affected, resulting in inadequate projection area. The resulting image will be one of a bright center surrounded by darkness. Hence, whether or not the camera is truly a low-lux camera is an important deciding factor for low-light surveillance.
Considering the Options of Black/White Cameras or Day/Night, Color/Monochrome Cameras
Aside from the camera's built-in low-light capabilities, the CCD sensor also has a wide spectrum range, making it sensitive to both visible and IR light. Hence, it is capable of providing a clear monochrome image in both low-light and nighttime conditions. When used with a day/night, black/white camera, it is able to transmit signals in color. The
CCD sensors separate signals into the primary colors of red, blue, and green to create a color image output within the visible light spectrum. Current technology makes it possible to digitally set day/night, color/monochrome sensitivity to IR lights.
Hidden Requirements when Setting Up Low-Light and
Night-Vision Surveillance
A skillful application of masking technology will allow IR lights to only cover the area, building, or infrastructure that requires surveillance, and prevent light from escaping and disturbing the community, or creating light pollution in the recorded images/video. Optical sensing lights that are either sensitive to light or sensitive to heat can be set to be triggered only when ambient light falls below critical levels, or when someone suspicious approaches.
High-Speed Positioning of IR Cameras
CCD cameras are decreasing in size and lenses are, in turn, becoming increasingly sophisticated. They now feature multiple focal and distance settings. The decreasing size and weight of cameras and lenses allows the camera mount to be more flexible. It is now possible to preset the angles and positions, such as
PTZ and IR camera features. When used in conjunction with IR cameras or IR illuminators and various preset triggers, it is possible to set IR night-vision cameras to point at the scene in question in "real time."
Compatibility Between Cameras and Lenses
Cameras are generally equipped with automatic shutter modes and AES and AGC features. These features can supplement night-vision recording and other end-user requirements. Another requirement of night-vision surveillance is that the lenses should have automatic aperture modes so that it can automatically adjust to the light differences between day and night.
Camera Power Supply Requirements
Front-end power supply of the surveillance system should be unified. When IR illumination is used, considerations include IR lights, IR LED, and the current and voltage of the power supply. The distance of the cable also affects the system since currents weaken over transmission distance. If there are a lot of IR lights far away from the main power supply, using a central power supply of DC12V may cause the voltage of the lights closest to the power supply to be overly high, while those farther out are considerably weaker. In addition, fluctuations in voltage may shorten the lifespan of IR lights.
At the same time, when the voltage is too low performance may be affected due to inadequate light and distance projection. Hence, it is recommended to use a power supply of AC240V, as DC voltage fluctuations between AC100V-240V ensures a stable power output and stable performance of IR lights.
The last section continues to look at IR and night-vision installation and applications.
Things To Note When Installing IR and Night-Vision Cameras
IR and night-vision cameras are discreet and have a far-reaching scope and stable performance, if installed correctly. For instance, cameras should be installed away from direct light because IR lights are triggered by the amount of light hitting the IR pane. In addition, try to avoid having black objects, empty spaces, bodies of water, or other objects that absorb IR lights in the area. This is because if IR lights are absorbed or weakened, the quality of the camera's performance is largely reduced.
To optimize
IR or night-vision camera performance, pay attention to the following during installation:
1) Camera housing affects IR light performance, as light passes through different materials differently. For example, it should be kept in mind during installation that automatic defrosting glass weakens IR lights.
2) Avoid installing cameras in locations where there is direct strong light, such as sunlight and spotlights, to not only avoid the risk of overexposure, but prolong the lifespan of the CCD sensors.
3) IR cameras should avoid environments that are susceptible to radiation, dampness, dust, and extreme temperatures.
4) Some IR cameras only provide listings of power consumption rates, but do not include specifications for maximum distance or beamwidth. However, using power consumption as a measurement of the distance and beamwidth of IR lights is vague. Power consumption includes heat loss during the transmission process and from the lights themselves. The effectiveness of the optical glass also affects IR lights. Hence, the same IR lights may have vastly different projection distance and beamwidths.
5) As demand for IR illuminators rises, so has the number of manufacturers. However, camera manufacturer ratings are hard to compare as the technology and methods to do so differ between the manufacturers. Hence, it is crucial for end users to do their homework in terms of comparing products, reading installation manuals, and paying extra attention to safety precautions.
6) The amount of reflected light in the scene of surveillance is another factor to be considered. IR light shares the same reflection and refraction characteristics of visible light. Hence, the projection distance of IR light would be affected if the target scene does not contain buildings, walls, or signs that reflect light.
7) Simply considering the manufacturer's specified levels may not be enough to obtain desired results. As most IR illuminators on the market operate between wavelengths of 850nm and 940nm, cameras should be selected based on their sensitivity to these wavelengths.
8) The projection distance of IR illuminators is closely related to CCD sensors and their operating environments. Rain, fog, dust, and other weather conditions all affect projection distance. Moreover, the reflection between the environment and the target scene or object will also affect the performance of night-vision cameras, and is something that has to be carefully tested prior to installation.
9) Try and stick to electronic IRswitches, as many manufacturers use simple photosensitive systems to control the IR cut and switch the IR illuminators on or off. The use of an electronic smart chip to control the IR cut would enable more precise control settings.
Conclusion
IR and night-vision cameras are least affected by the migration to IP-based products in the security industry and are available in the form of network, SDI, and
960H cameras. There are also standards guiding the development and specifications of these cameras, further cementing their position as one of the mainstream products on the market.
