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OT - Infrared Illuminators

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  • OT - Infrared Illuminators

    I'm looking at infrared illuminators and they seem to come with either 850nm or 940nm LEDs. According to the web sites, the 850s are brighter and work better with IR cameras but have a "red glow" that is visible. Anyone have any experience with these to know how bright the red glow is? If a 60 LED illuminator can be seen in total darkness from 20 feet away then I need to use the 940s.

    Thanks.
    Steve
    Last edited by SteveF; 09-06-2011, 12:20 AM.

  • #2
    The glow will vary person to person. Some people can't see the 850nm, some, like myself, can see it pretty clearly.

    The brighter the IR LED, the more visible it will be. If you are using it for surveillance, people will probably not know what it is anyways.

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    • #3
      I can see the 850nm pretty clearly a lot further than 20ft in the dark! If you got a 60 led illuminator........well you are a red beacon

      940nm all the way, otherwise what is the point, might as well turn on the floodlight.

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      • #4
        Unfortunately it is impossible to take a picture that correctly depicts what the "red glow" looks like. Cameras, whether digital or film, do not have the same light response curve as our eyes.

        I have a security camera set up near the end of our road to observe the cul-de-sac. None of us that live on this hill can see it as none of our houses are near the road. The houses that are near the end of the road are all on long driveways radiating out from the cul-de-sac and down the side of the hill, except for mine. I have a level property but the dead end is about 300 feet from the house through heavy trees so I put a camera hidden in the trees. It is running on a wired twisted pair with baluns at each end. This is much superior to wireless as it doesn't pick up interference and ordinary cheap telephone wire can be used. I use 4 conductor drop wire so the other pair is used for power but you can buy baluns that transmit power and video over a single pair.

        I use the near IR illuminators with the red/orange glow. The camera has a 36 LED illuminator but that isn't enough since the end of the road is about 100 feet wide. To supplement the camera I built another illuminator with about 60 diodes in a six inch can with a fresnel lens on the front. This acts as a narrow beam spotlight on the road. It is mounted about 50 feet from the camera and runs on separate power.

        The IR spotlight is clearly visible if you are in the right place on the road but even a little to one side it disappears. The camera illuminator diodes are very dim and even with well accommodated night vision can only be seen by looking right at the camera. It isn't bright enough to attract attention.

        If you are walking with a hand torch you aren't likely to see them. If you are driving with lights on there is no chance of seeing them as your night vision will be destroyed by the headlights.

        IR illuminators don't provide much range unless you have something like my setup. The long wave LEDs appear about 2 to 3 times weaker since most cameras have much less sensitivity at that frequency. To obtain similar performance with the 940 nm LEDs you will need at least twice as many.

        This is what the night view looks like on my monitor. The arrow indicates a reflector I put on a neighbours's gate about 100 feet across the road.



        Don't expect sharp focus with IR unless the camera is designed with only IR in mind. The resolution of an optical system depends on the wavelength of light used and at IR frequencies it is about 1/4 of what it is in green light.
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          Before this past winter I helped install a security system at a museum which included night vision cameras, DVR's and infrared illuminators to paint the surrounding acreage at night. The red glow (to me) is very dim. You can see it barely but it definitely does the job it's designed to do. The resulting video that the camera captures looks like daytime on the monitors. Hope that helps!
          "To invent you need a good imagination and a pile of junk" Thomas Edison

          Better to have tools you don't need than to need tools you don't have

          73's KB3BFR

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          • #6
            Thanks folks, exactly what I needed to know.


            Macona - Earlier you modified a camera for IR photography. Have you tried taking pictures with an IR illuminator and how well did it work in a low light situation (preferably without long exposure times that might blur an object that was moving a little)?

            Thanks.
            Steve

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            • #7
              Just for reference here is the same camera with the sun coming up on the trees.

              Free software for calculating bolt circles and similar: Click Here

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              • #8
                Thanks for the photos. Looks like I'll have to do some experimenting with the type and amount of LEDs needed.

                Steve

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