Question 1

Can I drive multiple LEDs from one resistor?

Accepted Answer

LEDs in series can share one resistor: R = (Vs - n×Vf) / If, where n is the number of LEDs. The supply voltage must exceed the sum of all forward voltages. LEDs in parallel should NOT share a single resistor because manufacturing variations in Vf cause uneven current distribution—one LED may hog current and burn out. Use individual resistors for parallel LEDs.

Question 2

What happens if I use a resistor value that is too high or too low?

Accepted Answer

A resistor that is too high reduces current below the rated If, making the LED dimmer but not damaging it. A resistor that is too low increases current above If, reducing LED lifespan and potentially causing immediate failure. LEDs are rated for maximum continuous current (typically 20 mA for standard types); exceeding this shortens life exponentially.