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Can I trust in visual inspection to identify LED terminals?


LED Polarity: Why does this LED have the anode as the short pin?Can you identify this logo?Triple LED has only 4 terminalsIdentify high current LED Package nameAC current terminalsCan anyone identify this ICPower supply terminalsAre LEDs better than we think?Strange thing with 5mm LEDs and variable PSU






.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;








1












$begingroup$


enter image description here



In the figure above, LED A is a regular 5mm LED and the visual identification of its terminals polarity is well known.



enter image description here



enter image description here



As you can see, on LED B the anode is identified by the longer leg, but the other rules for visual identification are inverted.



I've confirmed the situation above with a multimeter.



I have no datasheet or reference for LED B.



I never saw an LED with these issues before.
Is LED B the result of a manufacturing error?



Thanks in advance.










share|improve this question











$endgroup$













  • $begingroup$
    Is it possible someone has trimmed sample B's leads after it left the factory? Anyway it's easy enough to test with a multimeter.
    $endgroup$
    – The Photon
    8 hours ago










  • $begingroup$
    In this case the leds are new and have all the same issue.
    $endgroup$
    – AmssmA
    8 hours ago










  • $begingroup$
    Are A and B the same color? What results do you get when you test with a multimeter?
    $endgroup$
    – The Photon
    8 hours ago










  • $begingroup$
    No they have different colors LED A e bright white and LED B e red. I don't have the leds now wtih me so i can not tell you the Vf values
    $endgroup$
    – AmssmA
    7 hours ago










  • $begingroup$
    I've yet to encounter an LED that had the anvil be positive, but I imagine they probably do exist.
    $endgroup$
    – Hearth
    7 hours ago

















1












$begingroup$


enter image description here



In the figure above, LED A is a regular 5mm LED and the visual identification of its terminals polarity is well known.



enter image description here



enter image description here



As you can see, on LED B the anode is identified by the longer leg, but the other rules for visual identification are inverted.



I've confirmed the situation above with a multimeter.



I have no datasheet or reference for LED B.



I never saw an LED with these issues before.
Is LED B the result of a manufacturing error?



Thanks in advance.










share|improve this question











$endgroup$













  • $begingroup$
    Is it possible someone has trimmed sample B's leads after it left the factory? Anyway it's easy enough to test with a multimeter.
    $endgroup$
    – The Photon
    8 hours ago










  • $begingroup$
    In this case the leds are new and have all the same issue.
    $endgroup$
    – AmssmA
    8 hours ago










  • $begingroup$
    Are A and B the same color? What results do you get when you test with a multimeter?
    $endgroup$
    – The Photon
    8 hours ago










  • $begingroup$
    No they have different colors LED A e bright white and LED B e red. I don't have the leds now wtih me so i can not tell you the Vf values
    $endgroup$
    – AmssmA
    7 hours ago










  • $begingroup$
    I've yet to encounter an LED that had the anvil be positive, but I imagine they probably do exist.
    $endgroup$
    – Hearth
    7 hours ago













1












1








1





$begingroup$


enter image description here



In the figure above, LED A is a regular 5mm LED and the visual identification of its terminals polarity is well known.



enter image description here



enter image description here



As you can see, on LED B the anode is identified by the longer leg, but the other rules for visual identification are inverted.



I've confirmed the situation above with a multimeter.



I have no datasheet or reference for LED B.



I never saw an LED with these issues before.
Is LED B the result of a manufacturing error?



Thanks in advance.










share|improve this question











$endgroup$




enter image description here



In the figure above, LED A is a regular 5mm LED and the visual identification of its terminals polarity is well known.



enter image description here



enter image description here



As you can see, on LED B the anode is identified by the longer leg, but the other rules for visual identification are inverted.



I've confirmed the situation above with a multimeter.



I have no datasheet or reference for LED B.



I never saw an LED with these issues before.
Is LED B the result of a manufacturing error?



Thanks in advance.







led identification polarity terminal






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 7 hours ago









SamGibson

12.5k4 gold badges18 silver badges44 bronze badges




12.5k4 gold badges18 silver badges44 bronze badges










asked 8 hours ago









AmssmAAmssmA

1521 gold badge2 silver badges11 bronze badges




1521 gold badge2 silver badges11 bronze badges














  • $begingroup$
    Is it possible someone has trimmed sample B's leads after it left the factory? Anyway it's easy enough to test with a multimeter.
    $endgroup$
    – The Photon
    8 hours ago










  • $begingroup$
    In this case the leds are new and have all the same issue.
    $endgroup$
    – AmssmA
    8 hours ago










  • $begingroup$
    Are A and B the same color? What results do you get when you test with a multimeter?
    $endgroup$
    – The Photon
    8 hours ago










  • $begingroup$
    No they have different colors LED A e bright white and LED B e red. I don't have the leds now wtih me so i can not tell you the Vf values
    $endgroup$
    – AmssmA
    7 hours ago










  • $begingroup$
    I've yet to encounter an LED that had the anvil be positive, but I imagine they probably do exist.
    $endgroup$
    – Hearth
    7 hours ago
















  • $begingroup$
    Is it possible someone has trimmed sample B's leads after it left the factory? Anyway it's easy enough to test with a multimeter.
    $endgroup$
    – The Photon
    8 hours ago










  • $begingroup$
    In this case the leds are new and have all the same issue.
    $endgroup$
    – AmssmA
    8 hours ago










  • $begingroup$
    Are A and B the same color? What results do you get when you test with a multimeter?
    $endgroup$
    – The Photon
    8 hours ago










  • $begingroup$
    No they have different colors LED A e bright white and LED B e red. I don't have the leds now wtih me so i can not tell you the Vf values
    $endgroup$
    – AmssmA
    7 hours ago










  • $begingroup$
    I've yet to encounter an LED that had the anvil be positive, but I imagine they probably do exist.
    $endgroup$
    – Hearth
    7 hours ago















$begingroup$
Is it possible someone has trimmed sample B's leads after it left the factory? Anyway it's easy enough to test with a multimeter.
$endgroup$
– The Photon
8 hours ago




$begingroup$
Is it possible someone has trimmed sample B's leads after it left the factory? Anyway it's easy enough to test with a multimeter.
$endgroup$
– The Photon
8 hours ago












$begingroup$
In this case the leds are new and have all the same issue.
$endgroup$
– AmssmA
8 hours ago




$begingroup$
In this case the leds are new and have all the same issue.
$endgroup$
– AmssmA
8 hours ago












$begingroup$
Are A and B the same color? What results do you get when you test with a multimeter?
$endgroup$
– The Photon
8 hours ago




$begingroup$
Are A and B the same color? What results do you get when you test with a multimeter?
$endgroup$
– The Photon
8 hours ago












$begingroup$
No they have different colors LED A e bright white and LED B e red. I don't have the leds now wtih me so i can not tell you the Vf values
$endgroup$
– AmssmA
7 hours ago




$begingroup$
No they have different colors LED A e bright white and LED B e red. I don't have the leds now wtih me so i can not tell you the Vf values
$endgroup$
– AmssmA
7 hours ago












$begingroup$
I've yet to encounter an LED that had the anvil be positive, but I imagine they probably do exist.
$endgroup$
– Hearth
7 hours ago




$begingroup$
I've yet to encounter an LED that had the anvil be positive, but I imagine they probably do exist.
$endgroup$
– Hearth
7 hours ago










2 Answers
2






active

oldest

votes


















4














$begingroup$

Super-Red (AlGaAs) LED dice are mounted the opposite way of most others, so they appear backwards from the silhouette of the leadframe.



The leadframe pin length should tell you the difference but there's been a case of one identified in another question here that's reversed even for that (presumably so they didn't have to buy two leadframe types or trim them differently- it's described in the datasheet so it's not an error).



So, the bottom line is "no" you can't trust anything that's not specified in the datasheet (and even then, stuff happens, I've seen a 1N400x diode with reversed markings, presumably dropped and replaced on the line- post test, pre-marking by a worker in Taipei where the factory was at the time).






share|improve this answer











$endgroup$














  • $begingroup$
    @ChrisStratton Maybe made all the same way? Some of the LED encapsulation is very manual and some less so, IME. Anyway, if it's supplied without a datasheet who knows. You buy 10K LEDs at the market in Shenzhen it's not necessarily the same as the next batch. Practically the Wild West out there.
    $endgroup$
    – Spehro Pefhany
    7 hours ago



















2














$begingroup$

Unfortunately manufacturers and LED's are all different, and there is not a good way to determine what the polarity is, I've seen datasheets that are wrong at times.



The best thing to do would be to use a digital multi meter with a diode tester, then reverse the polarity






share|improve this answer









$endgroup$

















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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    4














    $begingroup$

    Super-Red (AlGaAs) LED dice are mounted the opposite way of most others, so they appear backwards from the silhouette of the leadframe.



    The leadframe pin length should tell you the difference but there's been a case of one identified in another question here that's reversed even for that (presumably so they didn't have to buy two leadframe types or trim them differently- it's described in the datasheet so it's not an error).



    So, the bottom line is "no" you can't trust anything that's not specified in the datasheet (and even then, stuff happens, I've seen a 1N400x diode with reversed markings, presumably dropped and replaced on the line- post test, pre-marking by a worker in Taipei where the factory was at the time).






    share|improve this answer











    $endgroup$














    • $begingroup$
      @ChrisStratton Maybe made all the same way? Some of the LED encapsulation is very manual and some less so, IME. Anyway, if it's supplied without a datasheet who knows. You buy 10K LEDs at the market in Shenzhen it's not necessarily the same as the next batch. Practically the Wild West out there.
      $endgroup$
      – Spehro Pefhany
      7 hours ago
















    4














    $begingroup$

    Super-Red (AlGaAs) LED dice are mounted the opposite way of most others, so they appear backwards from the silhouette of the leadframe.



    The leadframe pin length should tell you the difference but there's been a case of one identified in another question here that's reversed even for that (presumably so they didn't have to buy two leadframe types or trim them differently- it's described in the datasheet so it's not an error).



    So, the bottom line is "no" you can't trust anything that's not specified in the datasheet (and even then, stuff happens, I've seen a 1N400x diode with reversed markings, presumably dropped and replaced on the line- post test, pre-marking by a worker in Taipei where the factory was at the time).






    share|improve this answer











    $endgroup$














    • $begingroup$
      @ChrisStratton Maybe made all the same way? Some of the LED encapsulation is very manual and some less so, IME. Anyway, if it's supplied without a datasheet who knows. You buy 10K LEDs at the market in Shenzhen it's not necessarily the same as the next batch. Practically the Wild West out there.
      $endgroup$
      – Spehro Pefhany
      7 hours ago














    4














    4










    4







    $begingroup$

    Super-Red (AlGaAs) LED dice are mounted the opposite way of most others, so they appear backwards from the silhouette of the leadframe.



    The leadframe pin length should tell you the difference but there's been a case of one identified in another question here that's reversed even for that (presumably so they didn't have to buy two leadframe types or trim them differently- it's described in the datasheet so it's not an error).



    So, the bottom line is "no" you can't trust anything that's not specified in the datasheet (and even then, stuff happens, I've seen a 1N400x diode with reversed markings, presumably dropped and replaced on the line- post test, pre-marking by a worker in Taipei where the factory was at the time).






    share|improve this answer











    $endgroup$



    Super-Red (AlGaAs) LED dice are mounted the opposite way of most others, so they appear backwards from the silhouette of the leadframe.



    The leadframe pin length should tell you the difference but there's been a case of one identified in another question here that's reversed even for that (presumably so they didn't have to buy two leadframe types or trim them differently- it's described in the datasheet so it's not an error).



    So, the bottom line is "no" you can't trust anything that's not specified in the datasheet (and even then, stuff happens, I've seen a 1N400x diode with reversed markings, presumably dropped and replaced on the line- post test, pre-marking by a worker in Taipei where the factory was at the time).







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited 7 hours ago

























    answered 7 hours ago









    Spehro PefhanySpehro Pefhany

    224k5 gold badges177 silver badges469 bronze badges




    224k5 gold badges177 silver badges469 bronze badges














    • $begingroup$
      @ChrisStratton Maybe made all the same way? Some of the LED encapsulation is very manual and some less so, IME. Anyway, if it's supplied without a datasheet who knows. You buy 10K LEDs at the market in Shenzhen it's not necessarily the same as the next batch. Practically the Wild West out there.
      $endgroup$
      – Spehro Pefhany
      7 hours ago

















    • $begingroup$
      @ChrisStratton Maybe made all the same way? Some of the LED encapsulation is very manual and some less so, IME. Anyway, if it's supplied without a datasheet who knows. You buy 10K LEDs at the market in Shenzhen it's not necessarily the same as the next batch. Practically the Wild West out there.
      $endgroup$
      – Spehro Pefhany
      7 hours ago
















    $begingroup$
    @ChrisStratton Maybe made all the same way? Some of the LED encapsulation is very manual and some less so, IME. Anyway, if it's supplied without a datasheet who knows. You buy 10K LEDs at the market in Shenzhen it's not necessarily the same as the next batch. Practically the Wild West out there.
    $endgroup$
    – Spehro Pefhany
    7 hours ago





    $begingroup$
    @ChrisStratton Maybe made all the same way? Some of the LED encapsulation is very manual and some less so, IME. Anyway, if it's supplied without a datasheet who knows. You buy 10K LEDs at the market in Shenzhen it's not necessarily the same as the next batch. Practically the Wild West out there.
    $endgroup$
    – Spehro Pefhany
    7 hours ago














    2














    $begingroup$

    Unfortunately manufacturers and LED's are all different, and there is not a good way to determine what the polarity is, I've seen datasheets that are wrong at times.



    The best thing to do would be to use a digital multi meter with a diode tester, then reverse the polarity






    share|improve this answer









    $endgroup$



















      2














      $begingroup$

      Unfortunately manufacturers and LED's are all different, and there is not a good way to determine what the polarity is, I've seen datasheets that are wrong at times.



      The best thing to do would be to use a digital multi meter with a diode tester, then reverse the polarity






      share|improve this answer









      $endgroup$

















        2














        2










        2







        $begingroup$

        Unfortunately manufacturers and LED's are all different, and there is not a good way to determine what the polarity is, I've seen datasheets that are wrong at times.



        The best thing to do would be to use a digital multi meter with a diode tester, then reverse the polarity






        share|improve this answer









        $endgroup$



        Unfortunately manufacturers and LED's are all different, and there is not a good way to determine what the polarity is, I've seen datasheets that are wrong at times.



        The best thing to do would be to use a digital multi meter with a diode tester, then reverse the polarity







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 7 hours ago









        Voltage SpikeVoltage Spike

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