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Thread: Watt vs Lumen

  1. #1
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    Watt vs Lumen

    Whats the difference? How many watts equal lumen or vise versa?
    2009 ASPECT 20
    2011 Rockhopper 29er

  2. #2
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    Lumens are a unit of measure for the amount of light produced by a light source, watts are essentially a measure of power used (1W=1Amp at 1 Volt). Most people think of a light bulb by its wattage because of how they are labeled at the store, but that's only one type of light source (incandescent). Different sources have different efficacies (lm/W), which should not be confused with efficiency, which is how much light gets out of the light fixture.

    LED manufacturers are touting their total lumen counts, not just in bike lights, but in all segments of the industry. The problem is that they say they have X amount of light but don't say where it is pointed and how strong it is. Think about a garden hose with a spray adapter. If the hose is 20 gallons per minute, how strong is the stream when you put it on jet vs mist? Obviously, the distribution of the water coming out of the hose has changed even if the flow rate has not. Similarly, a flood optic will spread its lumens over a larger area, which will appear less bright, than a spot, which will be a smaller, brighter area.

    A more helpful metric is the Center Beam Candlepower, which tells you how much light is coming out of the source. You can use this number to derive the amount of light (in footcandles or lux) at a given distance by simply plugging it into the Inverse Square Law. Simply saying I have a 1000lm light tells me nothing about where the light is going or how intense it is in a direction. Sadly, finding this information is difficult in parts of the industry where published photometrics are standardized, and impossible in bike lights.
    Last edited by Stockli Boy; 10-25-2013 at 05:33 AM. Reason: typo

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    @Stockli.

    Beautiful explanation! I'd like to add a bit though. This statement is a bit misleading. It really should say "LED light manufacturers...".

    Quote Originally Posted by Stockli Boy View Post
    LED manufacturers are touting their total lumen counts, not just in bike lights, but in all segments of the industry. The problem is that they say they have X amount of light but don't say where it is pointed and how strong it is.
    LED manufacturers do provide graphs of the spatial distribution of their product and typical lumen output at a specified drive current. The application of an optic or reflector when built into a light, alters the LED's distribution pattern and lumen output.

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    Quote Originally Posted by Cajun Rich View Post
    Whats the difference? How many watts equal lumen or vise versa?
    depends on LED quality. with good modern LED about 100 lumens per watt. older LEDs had much less than that.

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    Quote Originally Posted by Vancbiker View Post
    @Stockli.

    Beautiful explanation! I'd like to add a bit though. This statement is a bit misleading. It really should say "LED light manufacturers...".
    Yup. See what happens when I haven't had enough coffee? True enough, I jabbed my finger in the wrong eye.

  6. #6
    Action LED Lights
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    Stockli Boy,

    It sounds like what your looking for is the light distribution charts or Beam Patterns we have put together for all the lights we sell. Here is an example. For the whole collection follow the link above.

    Watt vs Lumen-gemini-duo.jpg
    Jim Harger
    Action LED Lights
    www.action-led-lights.com

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    Quote Originally Posted by Action LED Lights View Post
    Stockli Boy,

    It sounds like what your looking for is the light distribution charts or Beam Patterns we have put together for all the lights we sell. Here is an example. For the whole collection follow the link above.

    Click image for larger version. 

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    @Action Led....Those charts are great. It would be awesome to see charts on some of the competitive lights as well.

    If you are willing to test other lights and have the time to do so maybe people will be willing to send you thier lights to test and pay for shipping both ways so all you will have to do is test, repack light and return to owner. Everyone sends you their light fully charged and ready to run to minimize the turn around time. No need to recharge unless you need to rerun a test. .

    Just a thought.

  8. #8
    Action LED Lights
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    Right now is the peak of the light sales season and we have a hard time even squeezing in a bike ride. (Got to keep our priorities straight) But after the first of the year I'd love to.
    Jim Harger
    Action LED Lights
    www.action-led-lights.com

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    Quote Originally Posted by Action LED Lights View Post
    Right now is the peak of the light sales season and we have a hard time even squeezing in a bike ride. (Got to keep our priorities straight) But after the first of the year I'd love to.
    do you do those spatial distribution graphs yourself ? can you do them ( for reference purposes ) for some better known lights like L&M Seca, NiteRider Pro or Lupine ?

    would be nice to have an online tool to overlay the response graphs of any light over a well known light like that. similar to how L&M has a tool on their site to compare beam shots of various lights.

  10. #10
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    I'll look into doing the overlay.
    I sure I could squeeze in a few comparison lights if someone wants to loan them. I would do one day turn around.
    Jim Harger
    Action LED Lights
    www.action-led-lights.com

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    +1, and it depends on the driver.

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