[What's_nitro?]

All LEDs need resistors, as they are basically a short circuit otherwise (Light Emitting Diode). The voltage drop of an LED is pretty large- ~2.5 volts is pretty common, so at 5v you could get away without a resistor. Each string should have a 200-300 ohm resistor in it's series to limit current to 20-30 mA. This is more to protect the LEDs from popping than it is to prevent overdrawing the BEC circuit in an ESC. Patrick would know better than anyone if the lack of a resistor could cause a problem, and why.