SecurityWorldHotel

18/10/2012

Lighting for network cameras

Achieving a well-lit environment for network cameras during night time is not an easy task. The best way is of course to go out on scene and try out a chosen camera, lens and lighting combination in real conditions. However this is not always possible, but in reality, many systems that are set up during day time conditions may fail to achieve effective night-time images. Because of this, Raytec and Axis have created this practical guide, based on a series of test nights throughout the dark winter months of 2011 and 2012, which is designed to help users get a long way on the path to achieving perfect CCTV lighting for a network system at night.

The way to obtain adequate CCTV lighting for a network system at night time consists of several steps, with many things that should be kept in mind. However, this guide covers the most important points that will get security users really close to a good result.

Mounting the camera

Examples of good and bad positioning of the camera
Examples of good and bad positioning of the camera.

First of all, before you set your cameras rolling, it is vital that you have correctly mounted and aligned not just your cameras but your illumination too, for the best possible CCTV performance at night.

Cameras need to be placed in all kinds of locations and this requires a large number of variations in the type of mounting. Common mounting solutions include ceiling mounts, wall mounts, corner mounts, pole mounts and parapet mounts (used for roof-mounted housings or to raise the camera for a better angle of view).

When installing a fixed camera in an enclosure, it is important that the lens of the camera is positioned right up against the window to prevent any glare. Otherwise, reflections from the camera and the background will appear in the image. To reduce reflection, special coatings can be applied on any glass used in front of the lens.

Mounting the lighting Mount the illuminator first. Position the illuminator adjacent to the camera and point it towards the scene. Mount the illuminator at least 1 meter away from the camera (space dependent) to avoid reflection into the camera. Lighting must be mounted approximately 1 meter below dome cameras.

Do not position the PSU photocell facing illuminator or other direct light sources. The photocell monitors the ambient lighting conditions. Mount the PSU on a wall or flat surface with glands facing down. Flat, adapter plate brackets are available for mounting illuminator and PSU on a pole. Connect the illuminator to the PSU. Installers can extend or reduce illuminator cable length using appropriate cable and weather proof box.

Align your illumination with your camera at night for optimum image performance. Adjust vertical angle, and adjust horizontal angle using adaptive illumination to match the illumination to the camera field of view.

Reduces performanceMay cause hot spotsBest performance
Reduces performanceMay cause hot spotsBest performance

Match the illumination to the lens angle The reality is that most cameras need a certain level of lighting to produce an effective image at night. Even the most advanced cameras require dedicated lighting to produce images with the ability to detect, identify or recognize people or objects in the scene.

It is critical to have the right angle of illumination, matched to the camera field of view. A narrow light on a wide angle can produce a bright spot on the screen and wide angle illumination on a narrow scene results in light wastage and reduced performance.

Light off (70 metres)White-light on (70 metres)Infrared on (70 metres)
Light off (70 metres)White-light on (70 metres)Infrared on (70 metres)
Illuminated person (50 metres)Illuminated surrounding (200 metres)
Illuminated person(50 metres)Illuminated surrounding(200 metres)

Above are some examples of infrared and white-light CCTV Images – with the angle of illumination perfectly matched to camera field of view, with clear and even illumination, and no dark spots.

Infrared and focus shift Focus shift is a potential issue encountered when setting up camera systems for 24-hour performance using infrared. The different wavelengths of visible light (400–700nm) and infrared (700–1,000nm) create different focus points through the lens onto the camera chip.

This can lead to a loss of image focus at night, particularly if the camera is set up during daytime operation. The degree of focus shift depends on a variety of factors.

Focusing the camera correctly for low light performance means the camera will be focused for IR with the aperture fully open. During daytime operation the increased depth of field created by a closing aperture will counter the effects of focus shift. The best solution is to focus the camera using only infrared. This can be achieved by setting up the camera at night using infrared lighting and using an IR pass filter over the camera lens.

Lenses The choice of lens impacts the quality of image. Here are some pros and cons regarding lenses.

Pro: A camera with an auto iris lens (like many of the Axis cameras) is the common choice for achieving high quality images for 24 hour surveillance in external scenarios. The auto iris opens and closes to allow the right amount of light fall onto the camera chip dependent on whether it is day or night. Open at night to collect maximum light, more closed during the daylight.

Con: Auto iris lenses can often be slightly bigger, and more difficult to set-up.

Pro: Fixed lenses are often used for internal applications where light levels may be constant, and can be set to the specific scene requirements. The smaller the F-stop setting on the camera is fixed at (1.4 is typical for night time surveillance) – the wider the iris, therefore more light is let into the camera and it produces better night-time images. The camera will use an electronic iris during the day (like a shutter) to avoid too much light causing over exposure (white out) on a scene.

Con: Fixed lenses are not suitable for day/night or changing light scenarios. The iris opening cannot be adjusted. To compensate for changes in light, some cameras will adjust exposure time or gain, which can lead to motion blur or noisy images.

Lighting cost Consider the running and maintenance costs of your system. Many installations utilize multiple 300W or 500W illuminations. These can be replaced with as little as 40W of long life, cool running infrared or white-light LED illumination.

Not only does LED lighting have an inherently low power consumption, but it also lasts a lot longer – typically around 10 years and requires zero maintenance – compared to a halogen light which can last as little as five months. Over this ten year period, there are significant savings to be made on energy consumption, running costs, and labour.

Additionally, white-light can be targeted and directed exactly where needed. It can also be activated via an external trigger on a timer, to provide lighting only when needed for a predetermined amount of time to further save on energy usage and light pollution. This is referred to as "Lighting on Demand".

Street lights Often, users of security systems may consider street lighting to be a good enough solution to fully illuminate a scene for capturing CCTV images at night. The user may be cautious about adding additional visible illumination on scene because of light pollution concerns. For this scenario, infrared illumination which is invisible to the human eye can be a very effective solution.

Street lighting
Street lighting.
Infrared on.
Infrared on.

If there is too much ambient light on scene, or flashing lights nearby causing a disturbance to your CCTV image, using IR lighting with an IR band pass filter lens on the camera will cut out the glare from all other ambient light apart from IR, for a crisp and clear, evenly illuminated black and white image.

Excessive lux levels High performance, low light camera technology such as the Axis Lightfinder, requires as little as 1 or 2 lux of effectively directed, colour corrected white-light illumination. Many traditional "visible" lighting solutions aim for high lux levels on the scene – this is not always required and it can often result in reduced image quality, excessive light pollution and excessive energy consumption. NB: Typical lux levels for CCTV are between 3 and 7 lux.

Axis Lightfinder Technology. Image captured in absolute darkness with only 50 percent brightness.White-light off (50 metres).
Axis Lightfinder Technology. Image captured in absolute darkness with only 50 percent brightness.White-light off (50 metres).
White-light on (50 metres).
White-light on (50 metres).

Megapixel cameras There is one simple rule to remember, if all other variables stay equal – the resolution of a camera increases as its sensitivity to light decreases. This is due to the size of the individual pixels on a sensor (think of the pixel as a little bucket to collect light). Consider the two examples below:

Resolution Resolution

Clearly the sensor on the right with 16 pixels has 4 times the resolution of the sensor on the left with 4 pixels. But take a look at the size of the individual pixels on each sensor; the pixels on the sensor on the left are much larger, capable of collecting much more light and are therefore able to deliver better performance in lower light conditions. So, most higher megapixel cameras require increased light levels to achieve high quality night-time performance.

Bandwidth and storage As discussed earlier in this article, street lighting is not enough for high quality images at night – no matter how sensitive light the camera is.

For users of network cameras, if the images captured are noisy or pixilated due to insufficient lighting, compression is unable to work and therefore creates a higher amount of data to be transmitted -increasing bandwidth and storage costs.

Compression techniques such as H.264 work on compressing the raw data into smaller "chunks" to reduce bandwidth requirements. In simple terms compression works by replicating data from previous frames and only the pixels that have changed (due to colour or movement) are transmitted and updated in the live video image.

Most security professionals will be familiar with the noisy "white-noise" images that cameras produce when there is not enough light on scene. With each pixel changing frequently the camera is fooled into thinking there is constant movement throughout the image and this prevents video compression from working.

A fundamental benefit of professional lighting for network cameras results from delivering enough light to prevent noise in the image. In turn this provides higher quality pictures, allows compression techniques to work and substantially reduces bandwidth and storage requirements.

Quick start It can be forgotten how long it takes for many lighting systems to switch on. This can be critical to the security system. Metal halide lighting can take several minutes to fully warm up compared to modern quick start LED lighting, which provides an instant strike. Quick start LED lighting can be used as a deterrent to warn off criminals, triggered on alarm from devices such as PIR detectors. Technology such as metal halide illumination is simply too slow and not suitable for high security, lighting on demand applications.

Color rendition Other old style lighting technologies such as halogen and sodium lighting have a poor colour rendition. They produce a dull, uneven orange/yellow glow. This leaves CCTV cameras at a disadvantage, as they are unable to produce high quality, true colour images at night, with enough detail to identify and recognize a target on scene.

White-light LED technology delivers a cool white colour temperature which is close to the colour of day light and which is optimised for colour CCTV. It allows cameras to generate images with accurate detail and colour even at long distances.

Thermal and IR Thermal camera technology should not be used instead of IR – but alongside it. Both technologies have different purposes: Thermal to detect – infrared to identify.

For distance critical applications such as border surveillance, port surveillance, protection of critical infrastructure or military projects, thermal technology is often used to detect that a subject is present at great distances, based on detection of a change in temperature. When the subject moves into the zone covered by the infrared illumination, unlike thermal cameras infrared can be used to identify intruders and pick out details such as facial features or clothing.

Infrared.Thermal.
Infrared.Thermal.
Thermal.
Thermal.

Looking at the two thermal images below at 100 meters, we can see that a person is present, but we cannot tell if the person is a man or a woman or identify any facial features. Now looking at the IR image on the left, we can clearly see that the person is a young/middle aged white male, wearing jeans and a casual jacket.

Infrared illuminators, which throw IR light onto a scene and can be viewed with monochrome or day/night cameras, should not be confused with thermal imaging which detect infrared radiation (heat) and create images based on differences in surface temperature producing false colours from these temperatures to create an artificial image.

Conclusion If you are considering lighting for your network camera system, then this article outlines some of the key challenges that you may face when designing and installing your CCTV system, and provides top hints and tips for achieving the best night time performance. Every scenario is different, so it's always advantageous to trial your system before deciding on the final configuration.

About the sponsorsRaytec are world leaders in LED lighting and manufacture a complete range of infra-red and white-light LED illuminators for CCTV and general lighting applications. All Raytec illuminators use the latest SMT LED technology to improve the performance of any security system at night, delivering high quality images, a long 10 year life, low energy consumption, low running costs and zero maintenance. Raytec’s management team has over 40 years of experience in designing, specifying and selling lighting directly to over 60 countries, and all Raytec products are UK designed and manufactured.

For more information about Raytec's solutions, visit: www.rayteccctv.com

As the market leader in network video, Axis is leading the way to a smarter, safer, more secure world - driving the shift from analog to digital video surveillance. Offering network video solutions for professional installations, Axis’ products and solutions are based on an innovative, open technology platform. Axis has more than 1,000 dedicated employees in 40 locations around the world and cooperates with partners covering 179 countries. Founded in 1984, Axis is a Sweden-based IT company listed on NASDAQ OMX Stockholm under the ticker AXIS.

For more information about Axis' solutions, visit: www.axis.com


Comment of the month

Lennart Alexandrie, Editor in Chief, Detektor Magazine

Cybersecurity –a new buzzword for video surveillance providers

As technology development moves on at an increasing pace the security industry is constantly taking advantage of the progress. The migration from an analogue to a digital technology was a real game changer. Suddenly technology integration has become much easier and cost effective. User friendliness and flexibility seem to no long have any limits.  

Here, and, in the newly published edition of Detektor magazine 02/17, Lennart Alexandrie, gives his views on the cyber threat and how it might affect the security industry.

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