You will often see 1,000Ω (1k) resistors being used in electronics.
For every vote across a 1,000 ohm resistor, it will pass 1mA of current through it.
Some LEDs, such as blue, green, and white, are bright at relatively low current (about 2 to 5mA). So, 1,000 ohms is good to protect them from about 5V. Remember, those LEDs usually drop about 3V from the resistor.
Other LEDs, such as red, orange, and yellow, usually need more current to be bright. So, you would use a lower value resistor. Often 220 ohms to get the current closer to 13.6mA. Remember those LED colors tend to drop about 2 volts from the resistor.
