LED dimensions...T-1 3/4...

Discussion in 'Homework Help' started by dtvonly, May 2, 2013.

  1. dtvonly

    Thread Starter Member

    Dec 14, 2012
    What does the T-1 stands for in a "normal" 5mm LED? I looked at a few datasheet and did not see anything having to do with 3/4. Please clarify.

    Thank you.
  2. WBahn


    Mar 31, 2012
    The 5mm package is known as the "T-1 3/4" package. The "T-1" package is the smaller 3mm package. These are just package style designators. You can see that 5mm is ~1.75x3mm, which is probably related to the history of the name, but at the end of the day they are no just names for two particular package styles.
  3. bertus


    Apr 5, 2008
  4. RichardO

    Well-Known Member

    May 4, 2013
    The "1" part is the diameter in 1/8's of an inch. For instance, 1-3/4 would be 1.75 eighths of an inch or about 0.22 inches.

    The "T" part refers to the shape of the LED. There are many different shape designators possible but about the only one you will see for an LED is "T".

    This part numbering system dates back to the days of incandescent lamps! Some trivia: A lamp for a common room light is an "A" shape and a globe shaped lamp is "G".

    -- Rich
  5. WBahn


    Mar 31, 2012
    Close (and close enough)

    SIZE nominal inches mm
    T-3/4 2mm 0.090 2.3
    T-1 3mm 0.118 3.0
    T-1 1/4 4mm 0.160 4.1
    T-1 3/4 5mm 0.205 5.2
  6. #12


    Nov 30, 2010
    Oddly, the same method is used for fluorescent lamps and guitar necks. A T-12 fluorescent tube is 12 eighths of an inch in diameter and a Martin D12-20 guitar has a neck that is 20 eighths of an inch wide.
  7. WBahn


    Mar 31, 2012
    Not odd at all that it is the same as that used for flourescent tubes since it's use for LEDs stems directly from it being used for miniature lamps. As for the guitar necks, I think there are quite a few things that use something similar, namely sizes that are multiples of some base dimension. It's not surprising that, for things on this scale, that in the English units a base dimension of 1/8 would be used.

    In fact, I imagine it was precisely because such a base dimension was already in use for bulbs and lamps that stemmed from a time when the very notion of a lamp that was only 1/8" in diameter seemed absurd and that all lamps could always be an integer multiple of 1/8" that we have sizes that include fractions.

    It's actually quite ironic. The size designators were defined to avoid fractional sizes but eventually had to include fraction size designators.