Specifications Versus Real World Low Light Camera Performance
This post was updated on 11/27/2017 to reflect new cameras available.
The low light capability of an IP camera will determine if you can use the camera outdoors at night or inside with minimum lighting. This article reviews the IP camera specification for minimum light level and the factors that affect the low light performance.
Low-light sensitivity for IP cameras is defined as the lowest level of light that still provides reasonable video clarity. Most cameras will work well in the daytime or at normal room lighting, but we have to take a careful look at the specifications to determine if the camera will work when it’s dark. The low light sensitivity defined in the camera specifications can be misleading. IP camera specifications use lux (lx) to define minimum light level, but there’s more to the comparison than just the lux level.
What is Lux?
Illuminance or illumination is measured in metric units. Lux (Lx) is the measurement of actual light available. One Lux equals one lumen per square meter. This is a measure of light perceived by the human eye.
Here are some examples of typical lux values:
|light in lux||example|
|0.0001 lx||Moonless night with overcast night|
|0.002 lx||Moonless clear night sky with air-glow (star-light and other atmospheric effects)|
|0.01 lx||Quarter moon with clear night|
|0.05–0.36 lx||Light from a full moon on a clear night|
|6 – 10 lx||Street lighting|
|100-1,000 lx||Work-space lighting|
|10,000 lx||Surgery lighting|
|50,000 – 100,000 lx||Bright sunshine|
What affects the light sensitivity of a camera?
Low light sensitivity is determined by a number of different camera factors such as the size of the sensor element, the light transmission of the lens, signal to noise of the camera amplifier, and shutter speed.
As a rule of thumb the bigger the pixel elements the more light can be collected over a period of time. Unfortunately, as the resolution is increased the smaller each pixel element will be. This means that less light is collected by the individual pixel element. To increase the light capability, the size of the camera’s CMOS sensor must be increased. If we double the size of the elements, we will collect more light. For example, a ½-inch CCD sensor collects more light than a ¼-inch CCD sensor.
The larger the lens aperture and clearer the glass of the lens the better it can transfer the light. This light transfer capability is measured in f-number. The lower the f-number of the lens the more light is passed to the camera’s sensor. Conversely, the higher the number the less light is transferred. This means that an f 2.8 lens will pass 1/4 as much light as an f 1.4 lens.
Signal to Noise Ratio (S/N)
The small electrical signals from the sensor chip are amplified so they can be seen. The signal from the sensor varies depending on the ambient light. More amplification is required when the picture is darker, but this also can increase the noise.
Camera specifications usually indicate the amplification that they use to measure the light level. This is measured at IRE level. 100 IRE is the maximum level and the signal is at 100%. 30 IRE indicates the amplifier is providing a signal level of 30%. Since the noise level can be as high as 10%, we will see more noise in the video at lower IRE levels.
This electronic noise appears as graininess in your video. Better video circuits amplify the picture signal while adding very little noise. The result is measured using the SIGNAL-TO-NOISE RATIO (S/N) which is measured in dB units. The higher we can make the S/N ratio, the better.
Frame Rate and Shutter Speed
The time that the shutter is opened determines how much light falls on the sensor. By increasing the exposure time we increase the low light capability of the camera. As a matter of fact, you may see specifications that indicate very low light sensitivity but at very long shutter times. Be careful because we may not want to run a camera at a shutter time of 1 second. The longer the shutter is opened the more motion smearing will occur. Shutter speed or exposure time is also related to the frame rate. If a camera has a frame rate of 30 frames per second (fps), it has a maximum of 1/30th of a second to collect the light and convert it into a video signal. If the camera runs at 10 frames per second, the sensor chip would have 3 times longer (1/10 sec.) to “look” at the picture and absorb the light. Of course, the shutter speed can be set to a shorter time. Sometimes we have to compromise between low light performance and video smearing.
A wide angle lens (or a variable lens that is “zoomed out”) captures light from all over the scene. The f-number is affected by the lens angle. A close-up lens (or telephoto lens) catches the light from only a small part of the scene. Naturally, a lens that is zoomed out gives a brighter picture than one that is zoomed in. Normally you do not see this difference but in very low light situations, the focal length of the lens (how far it is zoomed in) affects the camera’s sensitivity.
The IP Camera Specifications:
Camera manufacturers try to make this simple by providing a minimum lux (lx) rating, but it is not that easy. What they should do is provide the Lux rating at a certain lens f-stop, frame rate, and IRE amplification level. Unfortunately, there is no uniform way that manufacturer’s measure their cameras and indicate the information on their specification sheets.
For example, the Axis P3364 low light specifications are:
|Axis P3364||light sensitivity|
|Color:||0.1 lux, F 1.2|
|BW:||0.02 lux, F 1.2|
Unfortunately, the specification doesn’t indicate the amplification level, shutter speed, or the frame rate used to determine the light sensitivity. It makes it difficult to actually compare to another camera.
On the other hand, let’s look at the specification provided by the Hanwha (Samsung) XNV-6085 dome IP camera.
|Hanwha XNV-6085||light sensitivity|
|Color:||Color : 0.004 Lux (1/30sec, F0.94), IRE 30|
|BW:||B/W : 0.0004 Lux (1/30sec, F0.94), IRE 30|
This provides much more information and allows us to make a better decision. This camera has enough low-light sensitivity to be used on a clear night with just starlight.
As you can see the low light capability of a camera is sometimes very difficult to determine from the specification, so that’s why we do the camera testing. It’s the only real way to determine the actual performance. Take a look at our IP camera test and review which compares Sony, Axis, Canon, and Hikvision cameras.
Summing it All Up
Light sensitivity is measured in Lux units. The less light available, the more sensitive the camera has to be. The lux value listed in the specification is not the only thing to consider. You need to look at the lens, shutter speed and signal to noise to make sure the camera will meet your requirements. A camera that sees down to 1 Lx, has the ability to see an image during early evening hours or just before dusk. A camera that’s down to 0.1 lx has the ability to see an image in let’s say a parking lot with some lights. A 0.05 lx sensitivity can enable a camera to actually see better than the human eye at night! To learn more about how the IP Camera works take a look at our video.
Need more information or help defining your IP camera system? Please give us a call at 1-800-431-1658 in the USA or 914-944-3425 everywhere else. You can also use our contact form to receive more information.