Tila Tequila

LED and resistor help.?

Ok, I have a 149 mcd – 5mm BLUE LED
3.8Vf @ 20mA

I want to use this LED as my power LED for the motherboard of a custom pc I’m building. Using a multimeter, I get a reading of 5V from the motherboard PWR LED header. I used the following formula to calculate the resistor needed to power my LED:

R = (Vs – VL) / I

I plugged in my numbers:

R = (5V – 3.8V) / 0.02A (= 60 Ohms.)

Therefore, I calculated I need 60 Ohms of resistance to properly power this LED. I just happened to have a 68 Ohm 1/8W resistor. I soldered the resistor to the positive lead of the LED and then wired the LED to the motherboard. The LED lit up perfectly fine!

Now here’s where I get lost. When I check the voltage after the resistor, I’m still getting a reading of 5V. Shouldn’t the resistor be lowering the voltage? What’s the point of the resistor if I’m getting 5V to the LED with AND without it?