The bench test 1: Lighting the way

It can be done of course, and there are a number of integrated day/night (IDN) cameras on the market, but the solutions we have seen so far generally involve significant compromise, complexity or cost. The basic problem is that colour CCD image sensors tend to have poor low light characteristics and even specially designed high sensitivity types produce a dull, grainy and usually noisy image at low light levels.

On the other hand monochrome cameras and image intensifiers can work down to extraordinarily low light levels but that is not much use if you require a colour image in normal daylight conditions. The usual answer is to illuminate the scene with visible or infrared light for low-light or night-time operation; it is simple, relatively cheap and it works, but it's a sledgehammer approach. Camera designers are continually striving for more elegant technology based solutions and the low light performance of colour models is improving all the time.

Much can be done with image processing – signal amplification and slow shutter/image integration systems for example – and several models have switchable colour/mono operation with motorised IR filters. But in an interesting example of lateral thinking the Canadian manufacturer Extreme CCTV has come up with a rather novel approach. The EX82DXL is one of several IDN cameras in the Extreme range with two image sensors and infrared illumination, in one self-contained unit. The monochrome camera and IR illuminators work together to produce an image in low light to dark conditions and it switches over automatically to the colour camera when light levels rise above a preset threshold.

Clearly with so much going on under the bonnet it is going to be a somewhat bulky and an unconventional shape. At first glance it looks a little like a police speed camera, though on closer inspection you can make out the bank of IR illuminators in the upper window, and the two camera lenses below.  The two cameras are based around a pair of mono and colour board modules with 1/3-inch CCD image sensors. Quoted resolutions are 420 lines for the B&W camera and 480 lines for the colour model. Normally at this point we mention the camera's low-light sensitivity but because this camera carries its own light source it is rated as a 0-lux design because it can literally see in the dark.

The spec claims a useable image with a mini- mum signal-to-noise ratio of 20dB at a distance of up to 45m from the front of the lens.

Both cameras are fitted with 4-8mm manual focus lenses with tele/wide adjustment; additionally the colour model has an auto-iris. IR light comes from no less than eighty-four 850 nanometre LEDs, which produce a visible dull red glow. Extreme also offers 940nm LEDs as an option. Day/night switching is triggered by a photocell mounted on the underside of the case.

The camera is powered by a 17-28v AC or 15-30v DC supply; the power feed and video output are combined into a single cable, which emerges through a weatherproof gland, also on the underside of the housing.

It is a fairly substantial device, measuring 130 x 134 x 212mm, or between four and six times the size of a typical general-purpose CCTV camera. The central part of the case is made from a lightweight alloy extrusion; it's fully weatherproofed and well protected. The front cover, held on by four screws, is an alloy casting; the transparent window is made from 1/4-inch thick Lexan and should be able to withstand all but the most determined physical assault. The rear cover is simply a blanking plate and like the front cover, is held on by four screws.

Inside the case the various modules slide in and out of the housing on chassis rails. At the front the two cameras and the IR illuminators are mounted on a simple frame and it can be released by slackening off three screws. This allows easy access to the two lenses. At the rear the video control boards for the two cameras, power supply module, LED and photocell adjustments are attached to a slide-out chassis, though this is normally fixed in place with screws and silicon mastic and cannot be removed.

The camera body is a fair size and it is no featherweight either with an all-up weight of 2.2 kg. Even so, installation shouldn't pose too many problems. Extreme can supply a wide range of mounting hardware options and our sample came with a sturdy looking bracket that should be no more difficult to fit than a conventional camera mount. On the underside of the unit there's a hefty mounting plate with three standard 1/4-inch mounting threads. Threaded mounting bosses are also inset into the sides of the case.

It's billed as a 'Plug and Play' design, which means there should be no need to make any internal adjustments. However, the well thought out instructions cover the available settings in some detail, which may be of interest to installers faced with setting up the camera in difficult lighting conditions. The rear panel gives access to controls for varying the light output from the infrared LEDs and changing the switch-over point for colour to black and white operation. The instructions also helpfully detail the layout of the camera control boards, even though these are not normally accessible from outside the case.

If necessary focus and tele/wide settings can be changed by removing the front faceplate cover and withdrawing the camera/light assembly. The colour camera's auto iris ALC and Level controls can also be accessed from the front of the unit. On the rear of the board module there is also a miniature DIP switch for the camera's backlight and auto exposure system, though the instructions suggest this should be left on the factory default setting.

The two lenses are separated by a distance of approximately 6cm there so there is a very slight parallax error between the colour and black and white cameras, however at a distance of more than a couple of metres it becomes virtually insignificant. The factory setup on our sample was on the button with negligible difference between the two fields of view. There is a brief loss of sync at the switch-over point but it only lasts for a fraction of a second and results in the loss of no more than one or two frames of picture information. In spite of the claimed higher resolution figure for the colour camera the black and white picture still managed to look a lot sharper, and a good deal less noisy over its range of lighting levels. Nevertheless the colour camera performed well with a crisp looking image and solid, natural colours in daylight conditions.

The auto iris and auto exposure systems both coped well with fairly rapid changes in lighting level though it could occasionally be confused by bright lights or large shadows in an otherwise well lit scene. Black and white operation is most impressive and the exposure system proved to be even more responsive. The IR illuminators kick in as soon as the camera switches to B&W operation and provide a bright and evenly distributed pool of light in front of the camera. The closeness of the light source to the camera lenses also means that there are very few shadows.

The scene remains well lit down to total darkness, at which point the camera really starts to show what it can do. Within the area of illumination the picture stays sharp, packed with fine detail, there's very little in the way of noise or grain and the contrast balance is spot on.

It gets quite warm, the IR illuminators generate a fair amount of heat but the internal modules are well spaced within the case, allowing free movement of cooling air, and the case makes an efficient heat sink so there shouldn't be any problems with overheating. In theory two cameras plus associated switching circuits means there is more to go wrong but build quality is excellent and in the absence of evidence to the contrary there's no reason to suppose it will be any less reliable than a conventional camera.

We have one small concern, and that's the internal wiring linking the boards. We were surprised to see that most of the plugs and sockets are of the non-captive variety and it is possible that one or more of them might work loose if the unit is subjected to vibration or repeated physical shock. Nevertheless our usual battery of intermittency tests showed nothing untoward.

What the manufacturer says ...
The EX82DXL is a powerful integration of two CCD sensors and 84 LEDs. An excellent colour picture by day is complemented with 40m infrared surveillance in total darkness. Integrated into a single housing, the IDN camera from Extreme CCTV will create, capture and control the light to ensure a high signal/low noise picture under all-day and all-night conditions.

The EX82 DXL is targeted at the CCTV market for applications ranging from 0 – 40m under any lighting condition. The integrated day and night design ensures high quality day-time images and zero lux mono night-time images. The EX82DXL ensures that picture quality is achieved on a 24-hour basis, ensuring effective coverage during the often-neglected vulnerable hours of darkness.

The achievable distance covers the perimeter of many residential and industrial applications where traditionally separate combinations of camera, lens, housing, bracketry and illumination are installed.

Often the illumination is either omitted from the specification or mismatched. The installer often hopes for the best under what-you-see-is-what-you-get conditions.

The EX82 is the world's first true day and night camera with integrated IR illumination, which delivers effective CCTV footage 24/7. It impacts at both a practical day-to-day and general industry awareness level. Low quality images during the night are not acceptable and as an industry we should continue to aim towards achieving effective footage at night as well as during the day.

Indeed, the Data Protection Act requires installers and end users to ensure their CCTV system is fit for the purpose and that the low-light night-time performance of the system is carefully considered. The advantages of infrared light are:

• No light pollution or unnecessary costly lighting
  
• Discreet or covert to blend with the surrounding environment
  
• Low installation and capital costs
  
• Increased return on investment by giving 24-hour coverage instead of just daylight coverage
  
• Designed to work in conjunction with a CCTV system.