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Making light of a dark place ...
Its important to remember that although humans, and indeed most other animals eyes are completely insensitive to Infra Red light, most Black and White capable CCTV cameras are varyingly efficient at producing images at covert wavelengths.
Although we cannot see this type of light, in practice it behaves in exactly the same way as visible frequencies.
Thats not to say that there arent a few interesting characteristics which need to be considered. In practice, many everyday objects appear very differently when illuminated purely with IR.
If you point a monochrome camera at a dense green tree in daylight, the foliage will appear extremely dark on screen; try the same exercise at night using only covert Infra Red illumination, and the tree may well look almost white.
If a fox happens to walk past, you may well think its been to the hairdressers to have blonde highlights put in! The fact is that apparently dark objects (such as vegetation) may well be highly Infra Red reflective, and so appear significantly brighter than under daylight conditions.
This in itself has benefits and disadvantages.
On the one hand, if an object is highly reflective to Infra Red, there is a strong possibility that the night image will be grossly overexposed in parts, and the camera / lens over compensation, may make it increasingly difficult to produce a clearly recognisable image of the target.
Though careful positioning of the Infra Red illuminator(s) and indeed some considered selection of the most appropriate type and power of lamp, may well restore some of the overall quality which is present under normal daylight conditions.
One obvious trick which Doktor Jon has been known to use on the odd occasion is perhaps also worth considering.
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