Why do CCTV IR LED’s Shine Red?

The use of infra red (IR) lighting with CCTV systems can give a massive boost to the night time performance but it can also give a really crappy image with a bright hot spot in the middle of the image, which can be avoided as detailed here.

The actual red shine that can be seen if you look directly at the IR light source is due to the light being in the upper limits of our eyes visible spectrum. Our visible light spectrum is 400nm-750nm. The IR LED emits light around 850nm, which is in the ‘near visible’ spectrum, which means we cannot see any light cast on a surface from it but can see the light if we look at the source.

imageTo avoid this light being visible, use an illuminator with a wave length of 940nm or higher. However you must ensure that camera you are using can see in this range. This is not always easy to confirm and it can be found with by the term ‘relative spectral sensitivity’ Most recognised professional brands will be compatible but it is not a given so it pays to do the research.

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  1. John Honovich August 29, 2011 at 2:10 am #

    But 940nm IR illuminators are harder to find and have much shorter range compared to 850nm, everything else being equal.

    • Tim Norton August 29, 2011 at 7:48 am #

      Thanks John

      I did not realise they had a shorter range. Most likely because the specifications state range as the primary feature over the power consumption.
      Do you happen to know the difference in power to achieve the same range?

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