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"Technical Section"
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Doktor Jons
Guide to Closed Circuit TV (CCTV)

Making light of a dark place ...
the inside track on Infra Red.

How to use Infra Red effectively

Before actually looking to use Infra Red, it’s important to understand what light frequencies the individual camera is capable of imaging, so a quick call to the manufacturer (or supplier), should give an indication of ‘spectral sensitivity’, in other words, how well a camera's imager will work under a particular frequency of Infra Red light.

It’s perhaps worth briefly mentioning that for those CCTV systems primarily intended to act as a visible deterrent, it may be preferable to simply use high output 715nM IR lamps with their bright red glow, rather than the covert ‘black light’ 850+nM equivalents.

Having decided on where to place the correct camera/lens combination, the next task is to identify where best to install and indeed direct, the Infra Red lighting.

Remember to exploit whatever areas of reflectence may be present (in fact highly reflective ‘dead areas’ should be deliberately excluded from the camera view) to achieve the most even and gentle illumination possible.

As an example, if a camera is installed to look at the paved area directly in front of a property, try pointing a 2-300W IR lamp at the building (preferably at around a 45 degree angle) with a minimum seperation of about 2 - 3 metres.

The reflected light will provide a nice clear image, with none of the harsh shadows, and intense reflectance that would occur, if the lamp is pointed directly at the area under observation. This technique is particularly useful for cameras with wide or ultra wide angle lenses.

On this point, always make sure that the illuminator is capable of throwing out the correct width beam for the lens being used. Too wide and the lighting level may be too low; too narrow, and the picture will not be correctly exposed from edge to edge.

Power supplies for Infra Red lamps >>

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