Why we should use three resistors not one in parallel

You *should* use a separate resistor for each LED string but this example doesn’t necessarily explain why. Trying to use the same value resistor in these configurations will severely limit the current through each LED on the right side but that’s just because it would need to handle 3 times the current since all the LEDs are passing their current through the one resistor now. If you replace it with a resistor 1/3 it’s value ie 33ohms then you’ll get the same current values in both the left and right circuits. A much bigger issue with using a single resistor is little variations between the LED forward voltages will essentially be amplified when using just a single resistor for all of them. If you modify one of the LEDs to have a Vf of 1.8V and another to have a Vf of 2.2V then you can see a bigger problem occur. The lower Vf diode will clamp the voltage at a lower threshold and make itself appear much brighter but restrict the current through other two LEDs. The LED with a Vf of 2.2V would have almost no current at all in this case and you’d see one bright LED, one dim LED, and one completely off LED. Also if you have a Vf as low as 1.8V and also use a lower value 33ohm resistor that one LED will draw significantly more current than is safe (about 70mA in this circuit)! Providing a current limiting resistor for each separate LED will result in the most uniform brightness and safest power distribution for all of the LEDs.

Thanks man:) now i can show off my gf

nice

Well just kidding. Thank you for explaining. I had no idea abt variations in leds and what it might cause.

Try this link, http://lednique.com/parallel-leds/ for an explanation of the issue with parallel leds

To more explicitly express one of the issues snowfats eluded to; if an led fails (perhaps from passing too much current) in a circuit where one resistor drives several leds the remaining leds will see an increase in current which can lead to a cascading failure.

Thats even a better illumination. Thanks