Simple dimmer for led light
You can use a potentiometer in series with the LED (or a series of LEDs) to increase or reduce impedance. From 0 to 1000 ohms. But you won't find a pot able to work with 16W. (look for power dissipation formula). Power dissipation is the power transformed into heat generated by the resistance when current is crossing the pot or a resistor.
Maybe several in parallel could work.