An LED lamp includes a first LED string and a second LED string connected in parallel to each other and a variable resistor connected in series with one of the first and second LED strings. The first LED string provides a first color temperature. The LED string provides a second color temperature difference from the first color temperature. The variable resistor includes a resistance track with resistance coils wound thereon and a slider moveable along the resistance track. When a position of the slider of the variable resistor is changed, an electric current flowing through the one of the first and second strings is changed accordingly to adjust the color temperature of the LED lamp.