Hey Guys!

I got a Question and a problem.

My question is lets say 5v Power supply, 3.4v LED 20mA.

so (5v - 3.4v)/0.02A = 80Ω

Now.. we need 80Ω but my question is what would be better to go under or over the needed ohms like in this circuit would it be better for the LED to put 20Ω or 180Ω resistor? also what happens if i skip the resistor all together?

The Problem.

I bought 50 "Super Bright" LED's (3.2v-3.6v, 20mA) off of eBay and they shipped with 50 free 510Ω Resistors.. Wanting to hook this up to my car (12v)

So.. with what i have

(12 - 3.2)/20mA = 440Ω
(12 - 3.6)/20mA = 420Ω
-----------------------
420Ω-440Ω resistor needed

Buuuuuuuuut i have 510Ω...
and if i run them in series it seems to get worse.

Anyone got any ideas on how i can make this work without having to wait for more resistors?