Public space CCTV schemes have been known to have major problems with yellow fluorescent street lighting in the past. Many cases have been documented where the colour generated has simply played havoc with CCTV video and the quality of images.
Local Authority specialist security contractors GD Security claim to have cracked the problem in a major system replacement project for Southwark, where 44 out of 50 cameras are being replaced with a winning combination of Pentax 8~144mm day/night lenses with the Bosch LTC0610 camera.
With the launch of the DC iris day/night lens last year, Pentax intended to address this very problem. Due to the company's huge dominance of the town and city centre surveillance market in Britain, local authority CCTV managers were exerting significant pressure for a solution to sodium lighting to be developed, says Pentax UK's Ken Tremain.
Standard lenses are designed to focus daylight accurately at one point, the chip. If one introduces different types of light, such as IR, the lens is unable to focus on the chip. This results in the picture going out of focus. IR corrected lenses will accurately focus IR light onto the chip, but not daylight.
Pentax day / night lenses are designed to focus a much wider range of light types. Once the focus is correctly set, using whatever light is available at that time, the focus will remain correct. The subject is still correctly focused even if a different type of light is falling on the scene, day or night.
"Most scenes will have a number of different light sources affecting the picture at the same time," explains Ken Tremain. "You may have moonlight, yellow sodium lighting, halogen and possibly IR as well. Without using a day night lens you may find that certain parts of the picture are correctly focused, but other parts are not."
GD Security has something of a track record with local authorities and although their specialist area is turnkey systems and integrated solutions for public space management, MD Barry Jones says it is a problem they are well acquainted with.
He comments: "The Pentax lenses were non-negotiable, there was nothing else that would do and so we trialled JVC and Sony cameras as well as the Bosch units to see how they behaved in the sodium lighting. The local authority can be very pleased with the upgrade. The old system owed them nothing as it was first installed ten years ago, when the kind of lens technology we have now just wasn't available."
