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  • #16
    Bear with me on this one. If I have a Surefire that's rated at 175 lumens, how much candlepower is that and how did you calculate it?
    Security: Freedom from fear; danger; safe; a feeling of well-being. (Webster's)

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    • #17
      Originally posted by Mr. Security
      Bear with me on this one. If I have a Surefire that's rated at 175 lumens, how much candlepower is that and how did you calculate it?
      You must use a footcandle meter. Select a matte surface. The light-sensitive element is faced toward the surface and slowly withdraw about 2 to 6 inches until the meter reading (A) is constant. A second reading (B) is taken when the light-sensitive element on the surface facing out to measure the incident light. Reading A divided by Reading B gives an approximate value for the reflectance on the surface.
      CP= Footcandles X D(Superscript 2)
      (D= Distance in feet from source to illuminated surface.)
      Please remember: Inverse Square Law. The strength of a field or the intensity of radiation decreases in proportion to the square of the distance from its source.
      Mr. Security, that information comes from Philips "Lighting Handbook." I take it along with my guide on every survey I conduct.
      I normally recommend a "Lighting Consultant" visit the site and make this recommendations which are appended to my report along with other speciality consultants reports for a particular survey. We just can't wing it. That is why completed surveys are so expensive, minus travel, food and lodging.
      Enjoy the day,
      Bill

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      • #18
        Originally posted by Bill Warnock
        You must use a footcandle meter. Select a matte surface. The light-sensitive element is faced toward the surface and slowly withdraw about 2 to 6 inches until the meter reading (A) is constant. A second reading (B) is taken when the light-sensitive element on the surface facing out to measure the incident light. Reading A divided by Reading B gives an approximate value for the reflectance on the surface.
        CP= Footcandles X D(Superscript 2)
        (D= Distance in feet from source to illuminated surface.)
        Please remember: Inverse Square Law. The strength of a field or the intensity of radiation decreases in proportion to the square of the distance from its source.
        Mr. Security, that information comes from Philips "Lighting Handbook." I take it along with my guide on every survey I conduct.
        I normally recommend a "Lighting Consultant" visit the site and make this recommendations which are appended to my report along with other speciality consultants reports for a particular survey. We just can't wing it. That is why completed surveys are so expensive, minus travel, food and lodging.
        Enjoy the day,
        Bill
        All I can say is, "I am glad someone with your indepth knowledge and experieance is willing to share what they have learned. Thank you."

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        • #19
          Originally posted by ACP01
          All I can say is, "I am glad someone with your indepth knowledge and experieance is willing to share what they have learned. Thank you."
          I second that. I thought I did well in physics, but I guess I missed a few lessons.

          There isn't going to be a quiz on this, is there? By the way, here's a layman's method for determining which flashlight is brighter: Simply point it at your eyes and turn it on for a moment. The longer you're blind the brighter the flashlight. (I know; not very bright - pun intended)
          Security: Freedom from fear; danger; safe; a feeling of well-being. (Webster's)

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          • #20
            All I can say is, I knew what a nanometer was, as well as monochromatic.

            All light can be measured in Kelvin. I learned this when I started playing with Photoshop, as well in studying photography, and playing with lasers.

            I'm not that well versed in measuring lighting in nanometer on the EM field, I'm usually describing lighting in Degrees Kelvin (3000-5000 or so) for getting rid of red eye and other crap.

            Thanks, Bill. Both for telling everyone what it was way better than I could, and for whipping out the Phillips Lighting Manual.
            Some Kind of Commando Leader

            "Every time I see another crazy Florida post, I'm glad I don't work there." ~ Minneapolis Security on Florida Security Law

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            • #21
              Originally posted by ACP01
              All I can say is, "I am glad someone with your indepth knowledge and experieance is willing to share what they have learned. Thank you."
              You are welcome.
              We are all in this together and there is more than enough work for all of us, so if we share, we all gain, if we don't, none of us gain.
              If you have a chance, please see if any of your company's management has any association with the Illumination Engineers Society-North America? Those folks are a godsend for us in this profession.
              Enjoy the day,
              Bill

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              • #22
                Originally posted by N. A. Corbier
                All I can say is, I knew what a nanometer was, as well as monochromatic.

                All light can be measured in Kelvin. I learned this when I started playing with Photoshop, as well in studying photography, and playing with lasers.

                I'm not that well versed in measuring lighting in nanometer on the EM field, I'm usually describing lighting in Degrees Kelvin (3000-5000 or so) for getting rid of red eye and other crap.

                Thanks, Bill. Both for telling everyone what it was way better than I could, and for whipping out the Phillips Lighting Manual.
                You and Mr. Security are most welcome. All of us in this business, security companies, security consultants should have a Lighting Manual at hand. I like Philips because they explain every aspect. I can not speak for other luminary makers.
                N.A., it is neat, the Kelvin scale its temperature scale has its zero point at -270 degrees Celsius.
                As for the explanation, it is so important in a survey when you are trying to help a fellow professional. Most of my training was at government expense for the work I was doing within the DOD and DOJ communities.
                Thanks again.
                Enjoy the day,
                Bill

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