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Infra red and low lux cameras (part 2): night vision security cameras

Infra red and low lux cameras (part 2): night vision security cameras
Regardless if you are looking for a color night vision security camera, or an infra red outdoor security camera, a complete, well-designed system depends on choosing the best and most suitable night vision security camera. Thorough consideration of the camera and its peripheral products — such as IR lights, lenses, protective cover, and power supply — is required prior to determining which model to choose.

Read the first part of this article: IR and low lux camera (1-1): Understanding low lux and night vision cameras

Regardless if you are looking for a color night vision security camera, or an infra red outdoor security camera, a complete, well-designed system depends on choosing the best and most suitable night vision security camera. The cost difference between an entry-level and high-end color night vision camera can range between US$200 and $5,000. Therefore, thorough consideration of the camera and additional peripherals — such as IR lights, lenses, protective cover, and power supply — is required prior to determining which model to choose.
The following section provides some guidelines to what you should consider prior to choosing and installing a low lux security camera.
 

Paying attention to the camera's aperture


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 affect color accuracy. Shutter speed also influences the amount of light that reaches the sensor. Shutter speed for night vision security cameras should be kept at 1/30 or 1/25 for nighttime surveillance. Slower than that would cause blurs and render the image unusable. Lenses with automatic aperture modes can automatically adjust to the light differences between day and night.


Security camera minimum illumination rating

A security 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. A potential problem can arise if the camera's minimum illumination rate is higher than the IR illuminator's spectrum. In this case, the effective distance will be affected and the resulting image will be one of a bright center surrounded by darkness.
When setting the lights and the infra red illuminators installers should pay attention how the IR lights cover the area that requires surveillance. IR light can bounce back from walls and blind the camera, or lights can escape and create light pollution in the recorded images/video.
The amount of light the camera is getting is another factor that could greatly impact a camera’s range performance. As a general principle, more light equals a better image and this becomes more relevant at longer distances. Achieving a good quality image requires sufficient built-in IR light, which consumes more power. In this case, it may be more cost effective to provide additional IR light to support the camera’s performance.
To save on power consumption, sensor triggered lights (light activated, motion activated or heat sensing) can be set to be triggered only when ambient light falls below critical levels, or when someone approaches the sensor.

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 ensure a stable power output and stable performance of IR lights.
It’s not all about specs and data sheets

Another common misconception is equating figures with performance. There is a tendency for end users to rely too heavily on camera data sheets when deciding what night vision camera to implement. In fact, users are often led astray by data sheets and make decisions based on metrics rather than how the camera actually performs. Unless comparing models from the same manufacturer, data sheets can be misleading and give no indication of the quality of the camera or how it will perform in the scenario, the only way to avoid this is to see the camera in action before making the final decision. If possible, it is best to do an onsite test where prospective cameras are evaluated to see how they perform in the area during day and night.
 
 

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