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Comparing lumens and candlepower?

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  • #76
    Re: Comparing lumens and candlepower?

    I came across this thread after doing a google search to try and find this answer. A co worker asked me about the relationship as I just showed him a new 240 lumen light that we in the technical scuba dive community refer to as a back up. It is an LED with an 8 degree beam angle that uses 3 AAA batteries.
    What seems to be the issue is that land use lights seem to be rated by the public in CP while we look for lumens and beam angles.
    It is hard to explain the different uses. Underwater, unless shooting video, you want nice tight beams. I have a 21 watt HID with a focusable beam from 6 to approx 30 degrees. five hour burn time and this thing cannot be turned on out of the water due to the heat that is generated.
    I also have a 12 watt LED rated around 1500 lumen with 4.5 hour burn time and a fixed 10 degree angle. Conditions will have a serious effect on lights. Clear water and the 12 watt LED and 21 watt hid are fairly close. Turbid water inside a wreck or where heavy particulates are present and the HID is like a laser beam that cuts through it. Much of the LED light is reflected back. But not because of power. Rather the beam angle is a huge factor in the ability to penetrate. I have another 230 lumen light with a 6 degree angle that compared to 1500 lumen LED is like a light saber. But it's all about the beam angle.

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    • #77
      Re: Comparing lumens and candlepower?

      Originally posted by Unregistered View Post
      Good morning and thanks for answering. I've read this entire thread, twice. And I still have not quite gleaned the information I THINK I need to pick a spotlight. It seems that with all the talk about angle, distance, 12.75, excel, computations, etc., that it all comes down to what I intend to use it for. I need a handheld spot for my boat used in the river. I need to see tree lines. I need to pick up channel markers (which are easier since they reflect), and it would be nice to see the log floating in front of me. At the same time, I want to reduce the glare off the bow and bow rail. Cost is important since I own a boat and all spare cash goes into the boat. Is 300 lumens enough? 750? Halogen? Or does nothing really matter? Can someone take all the technical facts and give some practical advice? Thanks!
      MRay
      It is inherently technical. If you don't want to get technical, then try this. You want to pick up objects at a distance and don't want a lot of light near you. You want to ignore lumens and look for very high candlepower, a direct rating of ability to illuminate at a distance. You want a beam angle that gives the right size spot at distance ranges you commonly work. For a boat, you probably want 10 or less. A 6 degree beam would light up a spot diameter which is about 10% of the object distance, 10' at 100'. An extremely narrow beam will be more like a laser pointer and not illuminate enough area.

      To light up a wide area right around you (essentially room lighting) choose by lumens and a large spot angle. Don't consider lights that have the wrong rating, lumens for spot lighting, or candle power for area lighting, because then you have to get technical. If you want to consider lights that only have the wrong spec type for your application, you have to get technical.

      Getting technical, but simple-technical:
      Lumens rate the ability to light up a whole sphere from the inside
      Candle power rates the ability to light up a (smallish) spot on the sphere, measured at the center of the spot.
      Beam angle defines how much of the sphere is lit up, and the beam angle you need tells you which of the other specs is the more relevant rating. If you like math AND know the beam angle, you can approximately compare lumen and candlepower ratings.

      The 12.57 (lumens/candela) figure is only the correct comparator when lighting the whole sphere. For a spot, the number is larger and may be hundreds of times larger. It is very similar to effective radiated power and beam angle for radio frequency antennas.

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      • #78
        Re: Comparing lumens and candlepower?

        Just as a practical comparison my section engineer recently bought a 'handlamp' with 2,000,000 candlepower.

        Mostly, in my opinion, bazillions of candle power is too often used to draw in the gullible buyer. This lamp takes close to 24 hours charge for less than 1 hour of use. It also requires the use of a shoulder strap to carry for any length of time. It looks like a regular handlamp only much much bigger. It does provide a good floodlight but only for a short period of time. In our case furnace inspections.

        Alternatively, I have a rifle lamp of 200 lumens. It fits into my trouser pocket. It lasts for up to 7 hours on a very short charge. It does the same job. There is only a narrower beam than the big one but it's good up to 90 metres.

        I am expecting delivery any day of an 800 lumens rifle lamp. One review by a shooter stated it illuminated deer at 400 metres. It also has a wide beam setting, reported as 100 metres wide, but I can't remember at what range.

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        • #79
          Re: Comparing lumens and candlepower?

          Lumens measure the amount of light that's spread around by a light source. Candela measure the brightest concentration in a focused beam. When I want to illuminate my house I compare lumens. When I want a driving light to reach out into the darkness and illuminate the stupid deer standing in the road, I want candela/candlepower. I see a lot of ads for driving lights quoting lumens. When you do the math to convert to candle power (like I used to get out of my Ciebies) the lumens they're selling are worthless. Might as well hang a flashlight out the window.

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          • #80
            Re: Comparing lumens and candlepower?

            Originally posted by Unregistered View Post
            ANSWER: 1 candlepower equivalent equals 12.57 lumens
            ----------------------------------------------------------------
            First of all nowadays we use the term CANDELA instead of candlepower.
            otherwise "Luminous Intensity" - (aka CandlePower)
            = 12.57 Lumens

            Details:

            We understand a candle radiates light equally in all directions, its output, in this consideration is not focused by any mechanical means (lenses or reflectors). Pretend for a moment that a transparent sphere one meter in radius surrounds your candle. We know that there are 12.57 square meters of surface area in such a sphere. Remember your Solid Geometry classes?

            That one candle (1 Candlepower/Candela) is illuminating equally the entire surface of that sphere. The amount of light energy then reflected from that surface is defined thusly:

            The amount of energy emanating from one square meter of surface is one lumen. And if we decrease the size of the sphere to one foot radius, we increase the reflected energy 12.57 times of that which fell on the square meter area.

            LUX is an abbreviation for Lumens per square meter.
            Foot-candles equal the amount of Lumens per square feet of area.

            So, that one candlepower equivalent equals 12.57 lumens.

            And for you figuring out LED equivalents, first you must know how many lumens your LED's each produce. Then divide that value by 12.57 and you have candlepower of the LED. You don't have foot-candles, remember foot-candles are illuminance.

            --------------------------------------------------------------

            SI photometry units
            Quantity ; Symbol ; SI unit ; Abbr.; Notes
            Luminous energy ; Qv ; lumen second ; lms ;units are sometimes called talbots
            Luminous flux ; F ; lumen (=*cdsr) ; lm ;also called luminous power
            Luminous intensity; Iv ; candela (=*lm/sr); cd ; an SI base unit
            Luminance ; Lv ; candela per square metre; cd/m2; units are sometimes called "nits"
            Illuminance ; Ev ; lux (= lm/m2) ; lx ; Used for light incident on a surface
            Luminous emittance; Mv; lux (= lm/m2) ; lx ; Used for light emitted from a surface
            Luminous efficacy ; lumen per watt ; lm/W; ratio of luminous flux to radiant flux

            A LIght Converter to play here here:
            www (dot)convertunits(dot)com/type/luminous+intensity

            and read about lights here:
            www(dot)theledlight(dot)com/lumens.html[/url]
            Sorry for the runaround on this can of worms.

            50 W HID gives you 20 million candlepower and 4500 HID lumens gives 15 million candlepower, so your light puts out somewhere between 20 and 15 million cp. Let's say 17 million, but because there is a wide tolerance on this value.

            I have learned from this exercise that the correlation between the listed watts, lumens and candlepower for HID spotlights is probably inaccurate or untruthful or both.

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            • #81
              Re: Comparing lumens and candlepower?

              I want to know how many lumen is 43,000 candlepower

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              • #82
                Re: Comparing lumens and candlepower?

                If what these other posts say is true, that a 1 lumen spherical light produces 12.6 candlepower, then the following equation (using simple geometry) will convert lumens to candlepower based on the angle of the beam (assuming uniform light within the beam):

                candlepower = lumens * 52,500 / (angle * angle)

                (where the angle is in degrees)

                So for example, a 520 lumens light with a 10 degree overall beam angle produces 273,000 candlepower.

                Comment


                • #83
                  Re: Comparing lumens and candlepower?

                  Originally posted by JohnS View Post
                  It is inherently technical. If you don't want to get technical, then try this. You want to pick up objects at a distance and don't want a lot of light near you. You want to ignore lumens and look for very high candlepower, a direct rating of ability to illuminate at a distance. You want a beam angle that gives the right size spot at distance ranges you commonly work. For a boat, you probably want 10 or less. A 6 degree beam would light up a spot diameter which is about 10% of the object distance, 10' at 100'. An extremely narrow beam will be more like a laser pointer and not illuminate enough area.

                  To light up a wide area right around you (essentially room lighting) choose by lumens and a large spot angle. Don't consider lights that have the wrong rating, lumens for spot lighting, or candle power for area lighting, because then you have to get technical. If you want to consider lights that only have the wrong spec type for your application, you have to get technical.

                  Getting technical, but simple-technical:
                  Lumens rate the ability to light up a whole sphere from the inside
                  Candle power rates the ability to light up a (smallish) spot on the sphere, measured at the center of the spot.
                  Beam angle defines how much of the sphere is lit up, and the beam angle you need tells you which of the other specs is the more relevant rating. If you like math AND know the beam angle, you can approximately compare lumen and candlepower ratings.

                  The 12.57 (lumens/candela) figure is only the correct comparator when lighting the whole sphere. For a spot, the number is larger and may be hundreds of times larger. It is very similar to effective radiated power and beam angle for radio frequency antennas.
                  Lumens measure the amount of light that's spread around by a light source. Candela measure the brightest concentration in a focused beam. When I want to illuminate my house I compare lumens. When I want a driving light to reach out into the darkness and illuminate the stupid deer standing in the road, I want candela/candlepower. I see a lot of ads for driving lights quoting lumens. When you do the math to convert to candle power (like I used to get out of my Ciebies) the lumens they're selling are worthless. Might as well hang a flashlight out the window.

                  Comment


                  • #84
                    Re: Comparing lumens and candlepower?

                    I recently purchased a 1000 lumen flash light that puts my 500,000 candlepower q beam to shame

                    Comment


                    • #85
                      Re: Comparing lumens and candlepower?

                      Here is an excellent link to help you guys further understand why you aren't able to mathematically convert cp to lumens, [www].theledlight.com/lumens] it does a thorough job describing the process some of it in greater detail than has been described here or in an easier to understand method.

                      Bottom line you are asking how many feet(12 inches) are in a cup(8oz) it us an un answerable question.

                      Comment


                      • #86
                        Re: Comparing lumens and candlepower?

                        Originally posted by JohnS View Post
                        There is no way to answer without knowing the beam angle, or the spot size at some distance. Each gives you half the answer.

                        For a lightbulb that radiates in all directions 1 cd (candlepower) emits 12.57 lumens (4*pi) because that is the solid angle of a complete sphere). For a light that emits a moderately small angle of light, any type of spotlight or flashlight, you need the solid angle to relate the two units.

                        Candle power (properly called candela) measures the brightest part of the beam. Lumens integrate the candlepower at each angle and give the total light emitted. If you are trying to light up a room, lumens are what counts. If you are trying to throw light a long way, and small spot size or beam angle is acceptable, candlepower is what counts.
                        The last paragraph of this answer should help anybody that doesn't understand the difference. I was lost and needed help and it did it for me! I need a good spotlight for fishing at night so I need to look at candlepower. Thanks for making it simple!

                        Comment


                        • #87
                          Re: Comparing lumens and candlepower?

                          I understand that this is a highly technical mathematical problem, but for practical purposes....it doesnt need to be.

                          Take a 3 inch diameter spotlight rated at 1 million candle power and equate it with a 3 inch halogen beam rated in lumens. Use the same number for the parabola. It would at least give a laymans answer for comparison.

                          Better yet, take a 450 lumen spotlight and shine it into a light meter. Set the meter to "lumens". Change the distance from the meter until it reads approximately 450.
                          Then take a 3 million CP spotlight and shine it into the meter from the same distance. Read the lumens on the meter. That would tell you how those 2 spotlights compare, no?

                          If a simple light meter can solve this problem, why cant all of you mathematical brainiacs come up with a simple comparative solution?

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                          • #88
                            Just test them out and see which you like better than the other. I have a 500 lumen headlamp and a 2million candle power spotlight. I find the headlamp much brighter and not as yellow as the spotlight

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                            • #89
                              Okay guys, please help me out but remember the K.I.S.S. Method. All of this talk of lumens, candlepower, lux, etc has my head swimming like back in the day when I was studying X-ray and remembering the differences between REM, Rad, Roentgen, sievert, gray, etc.

                              i like to to do night photography. I am needing a light that will light up a spot on an object about 300 feet / 100 yards away so I can focus the camera as well as use the light source to "paint" light on the object.

                              Without getting into the inverse square law and such, will a 1 million cp light do the work. Sometimes I have to overcome fog attenuating the beam, so I would rather go a little heavy on the brightness than under.

                              Many thanks, and remember to keep it simple please.

                              Comment


                              • #90
                                Originally posted by Whatdoidonext View Post
                                Okay guys, please help me out but remember the K.I.S.S. Method. All of this talk of lumens, candlepower, lux, etc has my head swimming like back in the day when I was studying X-ray and remembering the differences between REM, Rad, Roentgen, sievert, gray, etc.

                                i like to to do night photography. I am needing a light that will light up a spot on an object about 300 feet / 100 yards away so I can focus the camera as well as use the light source to "paint" light on the object.

                                Without getting into the inverse square law and such, will a 1 million cp light do the work. Sometimes I have to overcome fog attenuating the beam, so I would rather go a little heavy on the brightness than under.

                                Many thanks, and remember to keep it simple please.
                                The answer depends on the beam angle or how big a spot you want to light up and how bright it needs to be. Determine the illumination you need (lux, or lumens per square meter) and the area (NOT distance) over which you need it (square meters). Multiply to get lumens. You need that many lumens and you need a spot (basically a reflector) that can focus to that size at that distance so NO lumens are wasted outside the desired area. If any lumens are wasted outside the desired area, you need more.

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