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Thread: Run Time Formula

  1. #1
    Join Date
    Oct 2002

    Default Run Time Formula

    I know for some of the "designated" testers out there that testing run times of flashlights, esp. LED's, can be a long and pricy process. While mowing my front lawn I was thinking about another way to get a rough estemate of the run time of any given torch. This new way would consist of a calculator and a mathematical formula, the only problem is I don't have the formula. Do any of you fellow CPFers know of a formula that would allow for this?

  2. #2

    Default Re: Run Time Formula

    You are mowing the front lawn of your igloo?

  3. #3
    Flashaholic* Quickbeam's Avatar
    Join Date
    Jun 2001

    Default Re: Run Time Formula

    Here's the mathematical formula I use for non-regulated LED lights. I call it "Doug's Law of LED Flashlight Runtimes" [img]/ubbthreads/images/graemlins/smile.gif[/img]

    Take the stated runtime by the manufacturer and divide it by 3 or 4. This is usually how long you will want to use the light before changing the batteries... This often seems to work as a good estimate.


    12 hours = 3-4 hours
    100 hours = 25-30 hours

  4. #4
    Join Date
    Jan 2001
    Mesa, AZ. USA

    Default Re: Run Time Formula

    How about run 4 tests per flashlight/battery combination. Test each brand of flashlight 2-3 times with 2-3 brands of common batteries. Throw out best and worst result and average the remaining results.

    State run time as:

    Hours until 90% brightness ("regulated run time")
    Hours until 50% brightness ("Half Life")


  5. #5
    * The Arctic Moderator * Sigman's Avatar
    Join Date
    Sep 2002
    "The 49th State"

    Default Re: Run Time Formula

    While talking to brite one about this (and his spelling - he's my son!) we were talking about the amps drawn by a specific LED or bulb, amp hours capacity of a specific battery, supply voltage, "unknown resistance" presented by the conductive path & switch...

    In a nutshell, he wants to know if there is a formula using the known values of components that could render an "estimated runtime"...

  6. #6
    Farewell our Curmudgeon Administrator Roy's Avatar
    Join Date
    Apr 2002
    Granbury, Tx USA

    Default Re: Run Time Formula

    You would first have to pick a definition for "run-time". I started using the 50% of max brightness value for a couple of reasons.

    First of all, I was used to working with "half-lives" in the nuclear business.

    Secondly, the brightness of a light has to change by a factor of two for the human eye to detect the change. Also using the 50% value for both regulated and non-regulated lights tells you the same thing. It is true, that for a truely regulated light, there will probably not be a second 50% decay in brightenss.

    It could be usefull to report a second run-time value that would indicate a time to really usefull, but lower level of light. Here again, a value would need to be agreed on...75%, 80%, 90% of max brightness. The 50% and 75% values for really regulated lights are almost equal!

    Reporting Run-Time as time to 50% brilghtness and (say) 90% brightness would tell you if the light was regulated or not.

    By the way, I became a "designated" tester after I purchased a logging DMM with a PC interface and also found out that my ISP would give me either a 5 meg web page or a 5 meg FTP site for free! Folks kept asking what the runtime was for different light, so I jumped in with both feet and started plotting runtimes for those lights in my collection. Kinda learned as I went along. [img]/ubbthreads/images/graemlins/grinser2.gif[/img]

  7. #7
    Join Date
    Jul 2002
    Boulder, Colorado

    Default Re: Run Time Formula

    And you're doing a great job Roy, keep it up!

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