So a diode is a constant-voltage device. If you put a resistor in series and run a line voltage above the diode's voltage than the current will be limited by o

So a diode is a constant-voltage device. If you put a resistor in series and run a line voltage above the diode's voltage than the current will be limited by ohms law. But, variable resistors that are rated for a lot of power (roughly half the power of the diodes at max brightness) will add to the BOM.