Urgent help ... Led query

Discussion in 'General Electronics Chat' started by krishnan_hari83, Jun 27, 2012.

  1. krishnan_hari83

    Thread Starter New Member

    Feb 11, 2012
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    Hi Friends,

    I am having a doubt in LED light.

    I saw 2 datasheets.

    1. 3.2V 120mA = 43.5 is the luminous flux value
    2. 2.8V 350mA = 20 is the luminous flux value

    If the current is increased with little change in voltage...how does Luminous flux decrease? Please help me
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    What is so urgent?

    Are these two datasheets supposedly for the same LED, or are these for different LEDs?

    My guess is that they aren't even the same color, or, if they are, that they are different materials that happen to emit about the same color.
     
  3. KJ6EAD

    Senior Member

    Apr 30, 2011
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    The two LEDs cited are different colors so they have different dopant chemistries which in turn means the band gap energies are different. In addition, the scale for measuring luminosity is weighted to favor the sensitivity of human eyes so two LEDs that may emit the same quantity of energy per time unit from a thermodynamic perspective will have very different luminosity specifications when measured on the weighted scale.

    http://en.m.wikipedia.org/wiki/Light-emitting_diode

    http://en.m.wikipedia.org/wiki/Lumen_(unit)
     
  4. krishnan_hari83

    Thread Starter New Member

    Feb 11, 2012
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    These are the two LEDs that I am comparing.

    KA-5630SELZ4S - Kingbright & LUW_JDSH.EC - OSRAM.

    There is some problem in Kingbright LED datasheet. So not able to provide you the pdf.

    Please tell me what are the technical details to be considered
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    How can we possibly do that?!

    The lead spacing is a technical detail that should possibly be considered. The viewing angle is a technical detail that might need to be considered.

    What technical details are particularly relevant depend entirely on what you are trying to do, information about which, you might notice, is more than a little lacking.
     
  6. krishnan_hari83

    Thread Starter New Member

    Feb 11, 2012
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    Dear Sir, do u mean to say that they have different packages ( 5630, 5050 ) that makes them have different values?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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  8. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Last edited: Jun 27, 2012
  9. WBahn

    Moderator

    Mar 31, 2012
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    No. I mean that you are asking for answers without really asking a meaningful question.

    Think of it like this. I come up to you and say, "I looked at two vehicle and one weighs 2500 pounds and gets 20mpg while the other weighs 3000 pounds and gets 24mpg. What are the details about the vehicles I should consider?"

    What would your answer be? Could you give any kind of a meaningful answer based on just that information? Wouldn't a meaningful answer require me telling you what is important in a vehicle to me? Am I hauling horses? Am I going off-road? Do I have children? Am I 6' 8" tall?
     
  10. krishnan_hari83

    Thread Starter New Member

    Feb 11, 2012
    21
    0
    I am sorry for bothering you guys with my nasty approach...

    I will explain the concept. I am given an LED LUW_JDSH.EC - OSRAM. I was asked to source the equivalent of the above LED. I was given two choices one is Kingbright LED & one is Winnerjoin LED. I was asked to choose an alternate to the OSRAM LED from the above two ( Kingbright & Winnerjoin ) choices.

    This is my concern. Kindly help me. Sorry I am not so knowledgeable. With the view of improving myself I joined this community.
     
  11. DMahalko

    Senior Member

    Oct 5, 2008
    175
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    The requirements of this question are so narrow and technical that this sounds like an on-the-job part-substitution request from a manager to a technical employee.

    How much are you paying per hour to do this research? Is PayPal okay? ;)

    (I'm just joking.)


    That looks familiar. :cool:

    I wrote and cited the sections on refractive index, emission shapes, and transition coatings, and the two light emission cone diagrams are my work.

    http://en.wikipedia.org/wiki/Light-emitting_diode#Refractive_index


    (Don't use your real email address with your Wikipedia username. I wish those LED manufacturers in India and China would stop sending me spam about buying or making LED fixtures. I DON'T BUILD 'EM OR BUY 'EM, PEOPLE. Yeesh.)
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    It's still the same situation. Once again, I ask what features should I consider in deciding which vehicle to buy?

    How can we possibly provide ANY meaningful advice when we have absolutely NO idea what is and is not important? That is perhaps the most useful "improvement" you stand to gain from this exercise they are putting you through -- that in engineering virtually every question has many different answers depending on the context in which the question is asked.

    How big should the fuel tanks for our new plane be? That depends! Are we designing a plane to carry lots of cargo short distances, or is our market going to be people that need to fly halfway around the world non-stop. Same question, very different answers.

    Why is the existing LED need to be replaced? Not available any longer? Too expensive? Just need to establish a second-source for contract purposes? Equivalent in what way? What was the original LED chosen in the first place? Does the wavelength matter? How important is having the same luminous intensity? How important is having the same forward voltage drop? The same current draw? The same viewing angle? The same package size? How much variance can there be an any or all of those parameters (and probably a dozen more) and still be considered acceptable?

    Without know what the purpose of this LED is in the circuit, we can't even guess. If it's being replaced because it costs to much and its sole purpose is to let the user see a light to tell them the power is on, then the things that you should consider are going to be primarily electrical and physical compatibility with the existing circuit. If the reason it's being replaced is because it is no longer available and the optical properties are what's important, then it might be acceptable to have to make significant modifications to the circuit in order to accommodate a suitable replacement.
     
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