Calculate LED voltage drop

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hello all,

i have simple question studying myself count not find way calculate it.
to use led 9volt battery calculated needed resistor of 350 omhs, have 1k omhs resistor , when put them on circuit leds light poor (as expected).

simulating everycircuit showed power dropped 1.89v after 1k resistor.

how find 1.89v ?


thanks !  :smiley-mr-green:

that informations on datasheet of led. must find graph or table must given current voltage drop of led x.


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