I have several LEDs I want to use from a single voltage supply. I can do the math and find the required resistor values, but here comes the question: My voltage supply is set at a max of 3 volts. One of my LEDs has a Vf of 3 volts, so calculations show a resistor of zero ohms to be used. Is it ok to run this LED without a resistor... or should the supply voltage always be higher and them be choked down with resistors?

The next question deals with the resistors themselves: does it matter if I choose 1/8 watt, 1/4 watt, or 1/2 watt resistors? They may all be labeled as say 1k ohm, but seem to behave differently in the actual circuit.