Thread: Infra red
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Old 11th July 2018
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Re: Infra red

The visible spectrum is generally held to be from about 390 nanometres (violet) to 750 nanometres (deep red), but this varies slightly from person to person and also depends on the intensity of light, (just as our hearing drops off at high and low frequencies).

Ultraviolet light spans the spectrum 10 nanometres to 400 nanometres, so shorter than that of visible light but longer than X-rays.

Infrared energy extends from the red end of the visible spectrum at about 700 ~ 750 nanometres to one millimetre.

Digital cameras are 'converted' to infrared by removing the infrared filter from the CCD. This filter is fitted to improve colour rendition, without which some colours (particularly strong reds and blues) would almost appear to glow or 'fluoresce' owing to the effects of the invisible infrared energy.

I am not sure of the spectral sensitivity of converted cameras, which in any case will vary from one type of sensor to the next, but I do know that many are used with software to detect subtle differences in temperature for fault detection in engines and electrical equipment, and in non-destructive testing. Their sensitivity is such that they can see temperature differences of a few C in castings at room temperature, so it would be safe to assume that their sensitivity goes far beyond any photographic requirements.

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