Wiring LEDs to a 120VAC wall outlet
Most common LEDs operate at about 20mA 

eg: https://www.adafruit.com/product/1793

3.4V forwards voltage so from a 5V "USB-shaped" supply you'd need to drop 1.6V - ar 20mA that's 80 ohms.  so use a 82 ohm resistor (0.05W or larger) for each LED 







simulate this circuit &ndash; Schematic created using CircuitLab