My goal is to flash a few white LED in serial using 9V battery.

Here are the specifications of this LED.

As I saw the Forward Voltage is 3.4V, but what does it really mean?

Can't I plug this LED into more than 3.4V battery without using resistor?

Also I know that max current of this 10mm LED is 300mA.

As I know during serial connection voltage is trying to split to each LED equally. But in parallel connection voltage is the same to each LED and current is growing up!

So tell me can I flash a few 10mm white LED without using a resistor?
If I can.. then tell me how many LEDs should I use?
So what is a solution?

  • \$\begingroup\$ There are a lot (a lot!) of questions answered about wiring multiple LEDs and how to power them. You should do a basic search here. But, in general, the resistor in a DC circuit for a LED is to limit the current it can draw. Because a LED will happily draw as much current as it needs to become a Smoke Emitting Diode (SED). If you insist on forging ahead with this question, you will need to provide a schematic you are thinking of. \$\endgroup\$
    – user65586
    Commented Mar 16, 2016 at 12:42
  • 1
    \$\begingroup\$ Possible duplicate of Calculate resistor for red Led in series and/or Do I Need a Series Resistor in Front of a Blinking LED? and/or wiring LED's in parallel - need series resistor? \$\endgroup\$
    – tcrosley
    Commented Mar 16, 2016 at 13:08

1 Answer 1


Forward voltage is a voltage necessary for LED to conduct electricity. If the voltage across your LED is 3.4V, it will draw as much current as it can, and burn out eventually. So you need to limit this current to 300 mA. If you have power source of 9V, it means you can fit 2 LED comfortably in series as they will need 6.8 V together. Remaining 9-6.8 = 2.2V will be over your current limiting resistor. Since your current is 300 mA, resistor value should be 2.2V/300mA = 7.3 Ohm!


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